Update 1: On May 16, 2024, the U.S. Department of Justice sent a proposed rule to the Federal Register to downgrade marijuana from a Schedule I to a Schedule III drug. This is the first step in a lengthy approval process that starts with a 60-day comment period.

Update 2: Two recent research studies were added to the “Studies on marijuana and driving” section of this piece on July 18, 2024.

As marijuana use continues to rise and state-level marijuana legalization sweeps the U.S., researchers and policymakers are grappling with a growing public safety concern: marijuana-impaired driving.

As of April 2023, 38 U.S. states had legalized medical marijuana and 23 had legalized its recreational use, according to the National Conference of State Legislatures. Recreational or medical marijuana measures are on the ballot in seven states this year.

The issue of marijuana-impaired driving has not been an easy one to tackle because, unlike alcohol, which has well-established thresholds of impairment, the metrics for marijuana’s effects on driving remain rather elusive.

“We don’t have that kind of deep knowledge right now and it’s not because of lack of trying,” says Dr. Guohua Li, professor of epidemiology and the founding director of the Center for Injury Science and Prevention at Columbia University.

“Marijuana is very different from alcohol in important ways,” says Li, who has published several studies on marijuana and driving. “And one of them is that the effect of marijuana on cognitive functions and behaviors is much more unpredictable than alcohol. In general, alcohol is a depressant drug. But marijuana could act on the central nervous system as a depressant, a stimulant, and a hallucinogenic substance.”

Efforts to create a breathalyzer to measure the level of THC, the main psychoactive compound found in the marijuana plant, have largely failed, because “the THC molecule is much bigger than ethanol and its behavior after ingestion is very different from alcohol,” Li says.

Currently, the two most common methods used to measure THC concentration to identify impaired drivers are blood and saliva tests, although there’s ongoing debate about their reliability.

Marijuana, a term interchangeably used with cannabis, is the most commonly used federally illegal drug in the U.S.: 48.2 million people, or about 18% of Americans reported using it at least once in 2019, according to the latest available data from the Centers for Disease Control and Prevention. Worldwide, 2.5% of the population consumes marijuana, according to the World Health Organization.

Marijuana is legal in several countries, including Canada, where it was legalized in 2018. Despite state laws legalizing cannabis, it remains illegal at the federal level in the U.S.

As states grapple with the contentious issue of marijuana legalization, the debate is not just about public health, potential tax revenues and economic interests. At the heart of the discussion is also the U.S. criminal justice system.

Marijuana is shown to have medicinal qualities and, compared with substances like alcohol, tobacco, and opioids, it has relatively milder health risks. However, it’s not risk-free, a large body of research has shown.

Marijuana consumption can lead to immediate effects such as impaired muscle coordination and paranoia, as well as longer-term effects on mental health and cognitive functions — and addiction. As its use becomes more widespread, researchers are trying to better understand the potential hazards of marijuana, particularly for younger users whose brains are in critical stages of development.

Marijuana and driving

The use of marijuana among drivers, passengers and pedestrians has increased steadily over the past two decades, Li says.

Compared with the year 2000, the proportion of U.S. drivers on the road who are under the influence of marijuana has increased by several folds, between five to 10 times, based on toxicology testing of people who died in car crashes, Li says.

A 2022 report from the National Transportation Safety Board finds alcohol and cannabis are the two most commonly detected drugs among drivers arrested for impaired driving and fatally injured drivers. Most drivers who tested positive for cannabis also tested positive for another potentially impairing drug.

“Although cannabis and many other drugs have been shown to impair driving performance and are associated with increased crash risk, there is evidence that, relative to alcohol, awareness about the potential dangers of driving after using other drugs is lower,” according to the report.

Indeed, many U.S. adults perceive daily marijuana use or exposure to its smoke safer than tobacco, even though research finds otherwise.

Several studies have demonstrated marijuana’s impact on driving.

Marijuana use can reduce the drivers’ ability to pay attention, particularly when they are performing multiple tasks, research finds. It also slows reaction time and can impair coordination.

“The combination is that you potentially have people who are noticing hazards later, braking slower and potentially not even noticing hazards because of their inability to focus on competing things on the road,” says Dr. Daniel Myran, an assistant professor at the Department of Family Medicine and health services researcher at the University of Ottawa.

In a study published in September in JAMA Network Open, Myran and colleagues find that from 2010 to 2021 the rate of cannabis-involved traffic injuries that led to emergency department visits in Ontario, Canada, increased by 475%, from 0.18 per 1,000 traffic injury emergency department visits in 2010 to 1.01 visits in 2021.

To be sure, cannabis-involved traffic injuries made up a small fraction of all traffic injury-related visits to hospital emergency departments. Out of 947,604 traffic injury emergency department visits, 426 had documented cannabis involvement.

Myran cautions the increase shouldn’t be solely attributed to marijuana legalization. It captures changing societal attitudes toward marijuana and acceptance of cannabis use over time in the lead-up to legalization. In addition, it may reflect an increasing awareness among health care providers about cannabis-impaired driving, and they may be more likely to ask about cannabis use and document it in medical charts, he says.

“When you look at the 475% increase in cannabis involvement in traffic injuries, rather than saying legalizing cannabis has caused the roads to be unsafe and is a public health disaster, it’s that cannabis use appears to be growing as a risk for road traffic injuries and that there seem to be more cannabis impaired drivers on the road,” Myran says. “Legalization may have accelerated this trend. Faced with this increase, we need to think about what are public health measures and different policy interventions to reduce harms from cannabis-impaired driving.”

Setting a legal limit for marijuana-impaired driving

Setting a legal limit for marijuana-impaired driving has not been easy. Countries like Canada and some U.S. states have agreed upon a certain level of THC in blood, usually between 1 to 5 nanograms per milliliter. Still, some studies have found those limits to be weak indicators of cannabis-impaired driving.

When Canada legalized recreational marijuana in 2018, it also passed a law that made it illegal to drive with blood THC levels of more than 2 nanograms. The penalties are more severe for blood THC levels above 5 nanograms. The blood test is done at the police station for people who are pulled over and are deemed to be drug impaired.

In the U.S., five states — Ohio, Illinois, Montana, Washington and Nevada — have “per se laws,” which set a specific amount of THC in the driver’s blood as evidence of impaired driving, according to the National Conference of State Legislatures. That limit ranges between 2 and 5 nanograms of THC per milliliter of blood.

Colorado, meanwhile, has a “permissible inference law,” which states that it’s permissible to assume the driver was under the influence if their blood THC level is 5 nanograms per milliliter or higher, according to NCSL.

Twelve states, most which have legalized some form of marijuana of use, have zero tolerance laws for any amount of certain drugs, including THC, in the body.

The remaining states have “driving under the influence of drugs” laws. Among those states, Alabama and Michigan, have oral fluid roadside testing program to screen drivers for marijuana and other drugs, according to NCSL.

In May this year, the U.S. Department of Transportation published a final rule that allows employers to use saliva testing for commercially licensed drivers, including truck drivers. The rule, which went into effect in June, sets the THC limit in saliva at 4 nanograms.

Saliva tests can detect THC for 8 to 24 hours after use, but the tests are not perfect and can results in false positives, leading some scientists to argue against using them in randomly-selected drivers.

In a 2021 report, the U.S. National Institute of Justice, the research and development arm of the Department of Justice, concluded that THC levels in bodily fluids, including blood and saliva “were not reliable indicators of marijuana intoxication.”

Studies on marijuana and driving

Over the past two decades, many studies have shown marijuana use can impair driving. However, discussions about what’s the best way to measure the level of THC in blood or saliva are ongoing. Below, we highlight and summarize several recent studies that address the issue. The studies are listed in order of publication date. We also include a list of related studies and resources to inform your audiences.

State Driving Under the Influence of Drugs Laws
Alexandra N. Origenes, Sarah A. White, Emma E. McGinty and Jon S. Vernick. Journal of Law, Medicine & Ethics, July 2024.

Summary: As of January 2023, 33 states and D.C. had a driving under the influence of drugs law for at least one drug other than cannabis. Of those, 29 states and D.C. had a law specifically for driving under the influence of cannabis, in addition to a law for driving under the influence of other drugs. Four states had a driving under the influence of drug laws, excluding cannabis. Meanwhile, 17 states had no law for driving under the influence of drugs, including cannabis.  “The 17 states lacking a DUID law that names specific drugs should consider enacting such a law. These states already have expressed their concern — through legislation — with drug-impaired driving. However, failure to name specific drugs is likely to make the laws more difficult to enforce. These laws may force courts and/or law enforcement to rely on potentially subjective indicators of impairment,” the authors write.

Associations between Adolescent Marijuana Use, Driving After Marijuana Use and Recreational Retail Sale in Colorado, USA
Lucas M. Neuroth, et al. Substance Use & Misuse, October 2023.

Summary: Researchers use data from four waves (2013, 2015, 2017 and 2019) of the Healthy Kids Colorado Survey, including 47,518 students 15 and older who indicated that they drove. They find 20.3% of students said that they had used marijuana in the past month and 10.5% said they had driven under the influence of marijuana. They find that the availability of recreational marijuana in stores was associated with an increased prevalence of using marijuana one to two times in the past month and driving under the influence of marijuana at least once. “Over the study period, one in ten high school age drivers engaged in [driving after marijuana use], which is concerning given the high risk of motor vehicle-related injury and death arising from impaired driving among adolescents,” the authors write.

Are Blood and Oral Fluid Δ9-tetrahydrocannabinol (THC) and Metabolite Concentrations Related to Impairment? A Meta-Regression Analysis
Danielle McCartney, et al. Neuroscience & Biobehavioral Reviews, March 2022.

Summary: Commonly used THC measurements may not be strong indicators of driving impairment. While there is a relationship between certain biomarkers like blood THC concentrations and impaired driving, this correlation is often weak. The study underscores the need for more nuanced and comprehensive research on this topic, especially as cannabis usage becomes more widespread and legally accepted.

The Effects of Cannabis and Alcohol on Driving Performance and Driver Behaviour: A Systematic Review and Meta-Analysis
Sarah M. Simmons, Jeff K. Caird, Frances Sterzer and Mark Asbridge. Addiction, January 2022.

Summary: This meta-analysis of experimental driving studies, including driving simulations, confirms that cannabis impairs driving performance, contrary to some beliefs that it might enhance driving abilities. Cannabis affects lateral control and speed — typically increasing lane excursions while reducing speed. The combination of alcohol and marijuana appears worse than either alone, challenging the idea that they cancel each other out.

Cannabis Legalization and Detection of Tetrahydrocannabinol in Injured Drivers
Jeffrey R. Brubacher, et al. The New England Journal of Medicine, January 2022.

Summary: Following the legalization of recreational marijuana in Canada, there was a notable increase in injured drivers testing positive for THC, especially among those 50 years of age or older. This rise in cannabis-related driving incidents occurred even with new traffic laws aiming to deter cannabis-impaired driving. This uptick began before legalization became official, possibly due to perceptions that cannabis use was soon-to-be legal or illegal but not enforced. The data suggests that while legalization has broad societal impacts, more comprehensive strategies are needed to deter driving under the influence of cannabis and raise public awareness about its risks.

Cannabis and Driving
Godfrey D. Pearlson, Michael C. Stevens and Deepak Cyril D’Souza. Frontiers in Psychiatry, September 2021.

Summary: Cannabis-impaired driving is a growing public health concern, and studies show that such drivers are more likely to be involved in car crashes, according to this review paper. Drivers are less affected by cannabis than they are by alcohol or cocaine, but the problem is expected to escalate with increasing cannabis legalization and use. Unlike alcohol, THC’s properties make it challenging to determine direct impairment levels from testing results. Current roadside tests lack precision in detecting genuine cannabis-impaired drivers, leading to potential wrongful convictions. Moreover, there is a pressing need for research on the combined effects of alcohol and cannabis on driving, as well as the impact of emerging popular forms of cannabis, like concentrates and edibles. The authors recommend public awareness campaigns about the dangers of driving under the influence of cannabis, similar to those against drunk driving, to address misconceptions. Policymakers should prioritize science-based decisions and encourage further research in this domain.

Demographic And Policy-Based Differences in Behaviors And Attitudes Towards Driving After Marijuana Use: An Analysis of the 2013–2017 Traffic Safety Culture Index
Marco H. Benedetti, et al. BMC Research Notes, June 2021.

Summary: The study, based on a U.S. survey, finds younger, low-income, low-education and male participants were more tolerant of driving after marijuana consumption. Notably, those in states that legalized medical marijuana reported driving after use more frequently, aligning with studies indicating a higher prevalence of THC detection in drivers from these states. Overall, while the majority perceive driving after marijuana use as dangerous, not all research agrees on its impairment effects. Existing studies highlight that marijuana impacts motor skills and executive functions, yet its direct correlation with crash risk remains debated, given the variations in individual tolerance and how long THC remains in the system.

Driving Under the Influence of Cannabis: A Framework for Future Policy
Robert M. Chow, et al.Anesthesia & Analgesia, June 2019.

Summary: The study presents a conceptual framework focusing on four main domains: legalization, driving under the influence of cannabis, driver impairment, and motor vehicle accidents. With the growing legalization of cannabis, there’s an anticipated rise in cannabis-impaired driving cases. The authors group marijuana users into infrequent users who show significant impairment with increased THC blood levels, chronic users with minimal impairment despite high THC levels, and those with consistent psychomotor deficits. Current challenges lie in the lack of standardized regulation for drivers influenced by cannabis, primarily because of state-to-state variability and the absence of a federal statutory limit for blood THC levels. European nations, however, have established thresholds for blood THC levels, ranging from 0.5 to 50.0 micrograms per liter depending on whether blood or blood serum are tested. The authors suggest the combined use of alcohol and THC blood tests with a psychomotor evaluation by a trained professional to determine impairment levels. The paper stresses the importance of creating a structured policy framework, given the rising acceptance and use of marijuana in society.

Additional research

Cannabis-Involved Traffic Injury Emergency Department Visits After Cannabis Legalization and Commercialization
Daniel T. Myran, et al. JAMA Network Open, September 2023.

Driving Performance and Cannabis Users’ Perception of Safety: A Randomized Clinical Trial
Thomas D. Marcotte, et al. JAMA Psychiatry, January 2022.

Medicinal Cannabis and Driving: The Intersection of Health and Road Safety Policy
Daniel Perkins, et al. International Journal of Drug Policy, November 2021.

Prevalence of Marijuana Use Among Trauma Patients Before and After Legalization of Medical Marijuana: The Arizona Experience
Michael Levine, et al. Substance Abuse, July 2021.

Self-Reported Driving After Marijuana Use in Association With Medical And Recreational Marijuana Policies
Marco H. Benedetti, et al. International Journal of Drug Policy, June 2021.

Cannabis and Driving Ability
Eric L. Sevigny. Current Opinion in Psychology, April 2021.

The Failings of per se Limits to Detect Cannabis-Induced Driving Impairment: Results from a Simulated Driving Study
Thomas R. Arkell, et al. Traffic Injury Prevention, February 2021.

Risky Driving Behaviors of Drivers Who Use Alcohol and Cannabis
Tara Kelley-Baker, et al. Transportation Research Record, January 2021.

Direct and Indirect Effects of Marijuana Use on the Risk of Fatal 2-Vehicle Crash Initiation
Stanford Chihuri and Guohua Li. Injury Epidemiology, September 2020

Cannabis-Impaired Driving: Evidence and the Role of Toxicology Testing
Edward C. Wood and Robert L. Dupont. Cannabis in Medicine, July 2020.

Association of Recreational Cannabis Laws in Colorado and Washington State With Changes in Traffic Fatalities, 2005-2017
Julian Santaella-Tenorio, et al. JAMA Internal Medicine, June 2020.

Marijuana Decriminalization, Medical Marijuana Laws, and Fatal Traffic Crashes in US Cities, 2010–2017
Amanda Cook, Gregory Leung and Rhet A. Smith. American Journal of Public Health, February 2020.

Cannabis Use in Older Drivers in Colorado: The LongROAD Study
Carolyn G. DiGuiseppi, et al. Accident Analysis & Prevention, November 2019.

Crash Fatality Rates After Recreational Marijuana Legalization in Washington and Colorado
Jayson D. Aydelotte, et al. American Journal of Public Health, August 2017.

Marijuana-Impaired Driving: A Report to Congress
National Highway Traffic Safety Administration, July 2017

Interaction of Marijuana And Alcohol on Fatal Motor Vehicle Crash Risk: A Case–Control Study
Stanford Chihuri, Guohua Li and Qixuan Chen. Injury Epidemiology, March 2017.

US Traffic Fatalities, 1985–2014, and Their Relationship to Medical Marijuana Laws
Julian Santaella-Tenorio, et al. American Journal of Public Health, February 2017.

Delays in DUI Blood Testing: Impact on Cannabis DUI Assessments
Ed Wood, Ashley Brooks-Russell and Phillip Drum. Traffic Injury Prevention, June 2015.

Establishing Legal Limits for Driving Under the Influence of Marijuana
Kristin Wong, Joanne E. Brady and Guohua Li. Injury Epidemiology, October 2014.

Cannabis Effects on Driving Skills
Rebecca L. Hartman and Marilyn A. Huestis. Clinical Chemistry, March 2014.

Acute Cannabis Consumption And Motor Vehicle Collision Risk: Systematic Review of Observational Studies and Meta-Analysis
Mark Asbridge, Jill A. Hayden and Jennifer L. Cartwright. The BMJ, February 2012.

Resources for your audiences

The following resources include explainers from federal agencies and national organizations. You’re free to use images and graphics from federal agencies.

• CDC’s main marijuana page.
• CDC’s marijuana data and statistics.
• Marijuana Drug Facts from the National Institute on Drug Abuse.
• Health Effects of Marijuana from the CDC.
• Learn About Marijuana Risks from the Substance Abuse and Mental Health Services Administration.
• Marijuana and Lung Health from the American Lung Association.
• Substance Use Disorder 101 from the U.S. Department of Health & Human Services.
• What You Need To Know About Marijuana Use and Driving from the CDC.
• Does marijuana use affect driving? from the National Institute on Drug Abuse.
• Drug-Impaired Driving from the National Highway Traffic Safety Administration.

The post Driving under the influence of marijuana: An explainer and research roundup appeared first on The Journalist's Resource.

Update: On May 16, 2024, the U.S. Department of Justice sent a proposed rule to the Federal Register to downgrade marijuana from a Schedule I to a Schedule III drug. This is the first step in a lengthy approval process that starts with a 60-day comment period.

Update: Originally published in April 2021, this piece was updated on Oct. 7, 2022, with information about President Biden’s announcement pardoning anyone convicted of federal marijuana possession, the 2022 mid-term election ballot initiatives and several new research studies. The map has also been updated.

Dr. Tauheed Zaman opens his presentation about marijuana with a photo of the Haight-Ashbury street sign, the historic part of San Francisco tied to the hippie and counterculture movements of the 1960s and 1970s, and where the clock is permanently set at 4:20. 

“It’s just to say that cannabis has really been in our communities and among my patients for a long time,” said Zaman, an addiction psychiatrist at the San Francisco VA Health Care System, during a 2021 virtual presentation hosted by the National Press Foundation for an audience of journalists participating in a fellowship on covering opioids and addiction. “And cannabis has historically also been quite controversial.” 

Marijuana use — and its potency — have only increased since the 1960s, research has shown. 

The percentage of people aged 12 years and older who reported using marijuana during the prior year increased from 11.0%  in 2002 to 17.5%, or 48.2 million people, in 2019, according to the report, “Key Substance Use and Mental Health Indicators in the United States,” published in September 2020 by the federal Substance Abuse and Mental Health Service Administration (SAMHSA). 

Marijuana is the most commonly used illegal drug among people aged 12 years and older, according to the SAMHSA’s  2019 national survey on drug use and health. It is the third most commonly used addictive drug, after tobacco and alcohol, according to the Centers for Disease Control and Prevention. “Illegal” in this case means the drug is not legal on the national level, although that is under consideration.

The House in December 2020 passed the MORE Act of 2020, a bill to decriminalize marijuana. Senate Majority Leader Chuck Shumer said the timeline for the bill is “soon” in an April 2021 interview with Politico.

On Oct. 6, 2022, President Joe Biden pardoned anyone convicted of a federal marijuana possession charge since it became a crime in the 1970s, and urged state governors to do the same for state offenses. He also asked the Secretary of Health and Human Services and the Attorney General to review how marijuana is scheduled under federal law.

As of February 2022, 37 states, District of Columbia, Guam, Puerto Rico and the U.S. Virgin Islands have approved medical marijuana or cannabis laws, according to the National Conference of State Legislatures, which keeps an up-to-date list of laws by state. Many state lawmakers continue to debate on marijuana legalization and decriminalization. NCSL provides an overview of this fast-evolving landscape in the U.S.

Marijuana is legal in 19 U.S. states and the District of Columbia. In the 2022 mid-term election, five more states — Arkansas, Missouri, North Dakota, South Dakota and Maryland — will decide on marijuana legalization, according to Ballotpedia, a nonprofit organization that serves as a digital encyclopedia of American politics.

In Oklahoma, a ballot measure that would have legalized marijuana and decriminalize marijuana possession won’t be on the 2022 ballot after the state’s Supreme Court ruling. State Question 820 will instead appear on a special state election in 2023 or in the 2024 election, according to Oklahoma Watch.

Research on medical benefits, or harm, lags behind the wider availability of cannabis products.

“So these are significant times for cannabis and cannabinoid research policy and health, and it is really important for us to delve into the research and also, as journalists, be able to disseminate what we know and what we don’t know and what the health risks are,” said Ziva Cooper, director of the UCLA Cannabis Research Initiative, during another webinar “Cannabis: Health Effects and Regulatory Issues,” hosted by SciLine in April. SciLine is a free service, connecting scientists with journalists, based at the American Association for the Advancement of Science.

To help journalists add scientific evidence to their stories about marijuana, The Journalist’s Resource has compiled research studies and information shared by experts in two recent virtual events: Zaman’s presentation, “Cannabis Use and Related Disorders,” and SciLine’s “Cannabis: Health Effects and Regulatory Issues” webinar, which included Cooper, Madeline Meier, an associate professor in the department of psychology at Arizona State University and Rosalie Liccardo Pacula, a professor and the Elizabeth Garrett Chair in Health Policy, Economics and Law in the Sol Price School of Public Policy at the University of Southern California.

Quick facts about marijuana — or is it cannabis? 

The cannabis plant has more than 100 known compounds, called cannabinoids. Cannabis plants have small, translucent, hair-like structures called trichomes that store all the cannabinoids. The effect of most of the cannabinoids on human brain and body is still not known. So far, only two cannabinoids have been well studied: tetrahydrocannabinol, or THC, and cannabidiol, or CBD. 

Although “cannabis” and “marijuana” are used interchangeably in everyday dialogue, they’re not quite the same. 

Cannabis is the broader term for all the substances derived from the cannabis plant, some of which could be without THC, including CBD products and terpenes. Meanwhile, marijuana, which is made of the dried leaves, flowers, stems, and seeds and can be smoked or prepared to a concentrated honey-like resin, has THC.  

Cannabis is the more accurate term to use if you’re talking about the industry and products derived from the plant, said Zaman.

Other cannabinoids such as cannabinol, cannabigerol, cannabidivarin are sold at some dispensaries, but have been studied in animals only. There is another set of chemicals in cannabis plants called terpenes, including Myrcene, Pinene, Linalool. They too have only been studied in animals and not humans. 

“There’s much more research to be done,” Zaman said. “Are there many other cannabinoids in there that can have a physiologic effect? Absolutely. I think we’re very early in understanding that.”

Why aren’t the other compounds studied in humans? There are two main barriers. 

First, marijuana is a Schedule I drug under the Federal Comprehensive Drug Abuse Prevention and Control Act of 1970, more commonly known as the Controlled Substances Act. Controlled substances are drugs that have the potential to be misused. They are categorized into five schedules, with Schedule I drugs having the highest potential for abuse.

“So researchers have to deal with a lot more regulation and a lot more barriers to study something that’s scheduled,” said Zaman.

The second barrier is the large number of chemicals in cannabis. 

“It takes a lot of scientific equipment and funding to really isolate each chemical and try to study them individually,” said Zaman. 

Cannabis is prepared in different ways. In addition to smoking it, it can be made into hashish, tinctures, hashish oil and infusions. Table 2 in this 2015 paper in JAMA, “Medical Marijuana for Treatment of Chronic Pain and Other Medical and Psychiatric Problems,” lists the different preparations. 

Cannabis-derived products aren’t to be confused with synthetic cannabinoids, which are sprayed on dried, shredded plant material to make fake marijuana, commonly known as K2 and spice. While synthetic cannabinoids are similar to the chemicals found in the marijuana plant and bind to the same brain receptors, they have a much more powerful effect. 

“Synthetic cannabinoids can lead to cardiac issues, renal issues, psychiatric issues, including psychosis, seizures and death,” said Zaman.

THC content in cannabis plants is increasing

THC is the main known psychoactive compound in the cannabis plants. The THC content of marijuana has increased in recent decades with new growing techniques. The rise has been well-documented and concerns health experts. 

In a November 2020 study, “Changes in Delta‐9‐tetrahydrocannabinol (THC) and Cannabidiol (CBD) Concentrations in Cannabis Over Time: Systematic Review and Meta‐analysis,” published in the journal Addiction, researcher Tom P. Freeman and his colleagues found that the quantity of THC in a typical gram of cannabis rose by 2.9 milligrams each year between 1975 and 2017 for all herbal cannabis, and by 5.7 milligrams each year for cannabis resin, which is a substance produced in the trichomes and can be used to make products like hashish. 

“Changes in THC concentrations over time could also influence the efficacy and safety of cannabis used for medicinal purposes, in the absence of standardized dosing information for illicit cannabis products,” the authors write. 

Meanwhile, the concentration of CBD in cannabis plants has remained the same, the study finds.

So what’s driving this increase? The answer isn’t simple. Pacula explained it this way: The vast majority of the people who consume of most intoxicating goods — whether it’s alcohol, cannabis or even some of the harder substances, is by the near-daily heavy users. They purchase the largest quantity of goods, but represent only about 20% of the total using population. This is known as the 80-20 rule. 

“Because heavy users are the largest purchasers, the industry is inclined to try to sell enticing products to that very small but frequently buying group of users,” said Pacula. “So are they responding to demand? If you’re talking about demand for this very small group of heavy, frequently using cannabis users, the answer is yes. They’re responding to that very small group. But usually when we think about cannabis use, most frequently, what we’re measuring in cannabis use is not those heavy daily users who are using large quantities frequently throughout the day.”

What about medical marijuana? 

“Medical marijuana” is a misnomer, said Zaman. In many instances, there’s little difference between medical marijuana and recreational marijuana.

“States that have legalized cannabis have said, ‘Well, we are calling it medical marijuana or medical cannabis because, under state law, we want to make it legal to get and, therefore, we’re calling it medical,’ but the content, in terms of cannabinoids might be quite similar to recreational marijuana,” said Zaman. 

But even though it’s called medical marijuana and consumers can buy it legally from a dispensary, customers may not be getting exactly what’s listed on the product label. 

In a 2015 study, researchers tested 75 edible marijuana products such as baked goods, beverages, candy or chocolate, purchased from dispensaries in San Francisco, Los Angeles and Seattle and found that only 17% had accurately labeled their THC content. 

“Greater than 50% of products evaluated had significantly less cannabinoid content than labeled, with some products containing negligible amounts of THC. Such products may not produce the desired medical benefit,” wrote lead author Ryan Vandrey in “Cannabinoid Dose and Label Accuracy in Edible Medical Cannabis Products,” published in JAMA. 

Even though labeling has improved over the years, “There’s still tremendous variability in terms of just THC or CBD content,” said Zaman. “But even if the CBD and THC were accurately labeled, there are so many other compounds in cannabis that are yet to be studied, measured.” 

Cannabis is not federally approved for treatment of any medical conditions 

To date, the federal Food and Drug Administration has not approved cannabis for treatment of any disease or condition. It has, however, approved three products related to or derived from cannabis:

• Cannabidiol, derived from cannabis and used to treat a rare form of childhood epilepsy. It’s marketed under the name Epidiolex, made by Greenwich Biosciences.
• Dronabinol, a synthetic cannabinoid marketed under the names Marinol, which was acquired in 2019 by India-based company Alkem Laboratories, although the company’s website doesn’t seem to be available, and Syndros, distributed by Benuvia Therapeutics, and used to treat anorexia and wasting in AIDS patients.
• Nabilone, a synthetic cannabinoid used for nausea and vomiting in patients undergoing chemotherapy. It’s marketed under the name Cesamet, made by Bausch Health.

These three medications are only available with a prescription. 

Even though cannabis products are touted to help with anxiety and stress, they are not approved by the FDA for any psychiatric conditions. 

In 2013, Zaman did six months of research to help the American Psychiatric Association write a position paper on cannabis use for psychiatric conditions and “all of that work basically boils down to one line, which is there are no current psychiatric indications for which any cannabis product has been proven to be helpful via rigorous scientific studies,” he said.  

That’s not because there have been a lot of negative studies showing that cannabis does absolutely nothing for many psychiatric disorders. But it’s because of the lack of studies, Zaman said.  

The association reviewed its position again in 2018 and still opposes the use of cannabis as a medicine for any psychiatric condition, “because there are so many associations with poorer mental health outcomes in some populations, and not enough studies really showing that there’s a long-term benefit in terms of mental health,” said Zaman. 

The American Society of Addiction Medicine, a professional medical society representing over 6,600 physicians, clinicians and associated professionals in the field of addiction medicine, has a wider ranging set of recommendations for medical professionals who treat addiction. 

Studies of note about health effects of cannabis

A widely cited and comprehensive report by the National Academies of Sciences, Engineering, and Medicine, a private, nonprofit organization, provides a rigorous review of research published between 1999 and 2017 on the health impacts of cannabis and cannabis-derived products, ranging from their therapeutic effects to their risks for causing certain cancers, diseases, mental health disorders and injuries. 

For instance, the report found evidence that patients who were treated with cannabis or cannabinoids were more likely to experience a notable reduction in pain symptoms. But it also found evidence that smoking cannabis on a regular basis is associated with more frequent episodes of chronic bronchitis episodes and worse respiratory symptoms. 

Most studies involving cannabis show an association between the substance and certain changes in the body, but are not able to show cannabis actually causes those changes.   Researchers, however, have established that cannabis does affect psychosis — auditory and visual hallucinations, paranoia and, for some people, disorganized thinking.

More than a decade ago, in a 2007 systemic review of 35 studies, researchers concluded that there was enough evidence “to warn young people that using cannabis could increase their risk of developing a psychotic illness later in life.”

In people who have a family history of schizophrenia or another psychotic illness. Several days of heavy dose use can be enough to develop psychosis in this population, Zaman said.

“So in patients who have a history of psychosis, either personally, or who have it in their families, I absolutely feel I have an obligation to share this information with them,” he said.  

In the May 2021 study, “Relationship Between Cannabis Use and Psychotic Experiences in College Students,” published in the journal Schizophrenia Research, researcher Abigail C. Wright examines the association between cannabis use and hallucinations and delusions in more than 1,034 students at Boston-area colleges between 2010 and 2017. 

They learned that “College students who reported more frequent cannabis use in the past week reported higher levels of hallucinations and delusional ideation. Moreover, those who reported using cannabis more frequently had more distressing delusional ideas, which were held with more conviction.” 

Cannabis use also is associated with preterm birth and low birth weight. 

A study of 5 million live births in California between 2001 and 2012 shows that babies whose mothers had been diagnosed with cannabis use disorder were more likely to be born prematurely and have low birth weights, compared with babies whose mothers didn’t use cannabis. 

“The most notable observation is that exposed infants were 35% more likely to die within 1 year of birth than unexposed infants,” write researchers Yuyan Shi, Bin Zhu and Di Liang in “The Associations Between Prenatal Cannabis Use Disorder and Neonatal Outcomes,” published in April 2021 in the journal Addiction. 

Researchers say their findings call for prenatal cannabis use disorder prevention, treatment and policies. 

“The American College of Obstetricians and Gynecologists committee has recommended that physicians encourage pregnant women to discontinue cannabis use including medical use,” the authors write. 

What about the association between long-term cannabis use and other physical conditions? 

A 2016 study looks at the number of physical health problems as a function of the duration of cannabis use. It finds that cannabis use over a long period — up to 20 years — was associated with periodontal disease but no other physical health problems by age 38. 

Marijuana use at an early age could have negative long-term effects

Research indicates that when people start using marijuana in adolescence, they are more likely to become addicted to it. 

The brain matures from back to front. People’s frontal lobes, which are associated with thinking, executive function, cognition and impulse control, aren’t fully developed until age 26, which means they remain vulnerable during adolescence. 

“We want to protect the brain as long as we possibly can from the influence of substances, including cannabis, alcohol, opioids, because we want these frontal lobes to have a chance to myelinate and develop properly,” said Zaman. 

In “Young Adult Sequelae of Adolescent Cannabis Use: An Integrative Analysis,” published in Lancet Psychiatry in 2014, Dr. Edmund Silins and his colleagues looked at the association between frequency of cannabis use before age 17 and outcomes such as high school completion, cannabis use disorder and depression among more than 2,500 participants in Australia and New Zealand. 

They learned that people who began using higher doses of cannabis at a younger age were less likely to graduate high school, go to college, attempt suicide and develop an addiction to cannabis and other illicit drugs.

“Prevention or delay of cannabis use in adolescence is likely to have broad health and social benefits,” the authors write. “Efforts to reform cannabis legislation should be carefully assessed to ensure they reduce adolescent cannabis use and prevent potentially adverse developmental effects.”

In a 2012 study, Meier and colleagues look at how IQ is affected by persistent cannabis use. They assessed people’s IQ in childhood, before any of the study participants began using cannabis, and then again in adulthood, after some used cannabis for many years.

“As these adolescent users continued to use for more and more years, they showed more and more IQ decline,” said Meier. “The long-term, persistent, adolescent-onset users lost about eight IQ points from childhood to adulthood.”

Can people get addicted to marijuana?

The simple answer is yes. About one in 10 marijuana users become addicted, according to the CDC. 

“When you look at people who start in adolescence — again, early on, before that brain development has finished — the rate [of addiction] goes up to 17% at some point in their lives,” said Zaman. “Amongst daily users, 25% to 50% develop a use disorder at some point in their lives, depending on the study that you look at.”

People can also experience marijuana withdrawal. 

“I’ve had many patients go through marijuana withdrawal, particularly when they get admitted to the hospital or travel and suddenly don’t have access to their usual cannabis products,” said Zaman. 

Symptoms of withdrawal include irritability, anger, aggression, anxiety, sleep issues, appetite issues, restlessness, depressed mood and at least one physical symptom such as abdominal pain, shakiness, tremors, sweating, fevers, chills or headaches.

Legalization

Pacula pointed out that U.S. states have treated cannabis as more of a commercial enterprise because there’s still a lack of clear science that shows it’s a dangerous substance. As a result, many of the regulations tend to focus on licensing, dispensary locations, hours of operation at the local level or laws that allow on-site consumption.

“Testing [of the products] is done, but it’s largely for mold and pesticides,” Pacula said. “And taxation has largely been based on the sale of volume of the good instead of on the major ingredients within the cannabis plant.”

She said five key public health regulations are missing: restrictions on ingredients and extractions allowed from the cannabis plant; restrictions on the amount that can be sold; collecting taxes based on the potency of cannabis instead of the amount sold; compliance checks; and regulation of advertising and the promotion of cannabis products. 

“These are all things that we pay careful attention to when we’re talking about tobacco and alcohol in our state regulations and are things that are often not as carefully addressed in cannabis regulations, thus far,” said Pacula.

Pacula and her colleagues showed in a May 2021 study published in the American Journal of Preventive Medicine that all U.S. states that have legalized marijuana allow a large number of THC doses per transaction — larger than what daily consumers typically use in a month.

“States concerned about public health and diversion should consider reducing sales limits and basing them on total tetrahydrocannabinol content across all purchased products,” the authors write in “Current U.S. State Cannabis Sales Limits Allow Large Doses for Use or Diversion.” 

7 tips for journalists 

1. Take caution when reporting on animal studies. Findings from animal studies usually don’t bear out in humans. “I think it’s really important to keep the community and the U.S. population informed of the fact that what’s happening in a petri dish is very different than what we expect to happen in a human,” said Cooper. 

2. When citing academic studies in online news articles, include a hyperlink. “I really appreciate it when the reporters directly link … to the actual paper,” said Cooper. “So frequently, this does not happen. And it’s really upsetting, especially if somebody is a researcher who wants to go look at the original paper.”

3. When comparing studies, pay attention to differences in study design and the products used. “It’s really important that, as a reporter, you take a look at the [academic] article and see how the paper has defined ‘frequent’ or ‘regular’ or ‘heavy’ cannabis use,” said Meier. “Because lots of times, we’ll see that in one study, we’re talking about 30 or more lifetime uses, and in another study, we’re talking about daily use for 20 years. You can’t compare those two studies.”

Look at whether and how well the authors address alternate explanations for their findings, she added.

Journalists also should take note of which cannabis products are studied “so that we have a sense of how much potency was involved in those products,” said Pacula. “Daily use of a low-potency product is not likely to have any negative, harmful consequences in terms of psychoactive effects and may be very therapeutic and beneficial. Daily use of a concentrate that has an average potency of 70% THC is a different thing.” 

4. Look at how your state regulates alcohol and look for parallels in cannabis regulations. “We have a large number of regulations in place for alcohol that target the at-risk and heavy drinkers. We do not have the same cautions developed in our states or current discussions for national legalization [of marijuana] to protect the typical consumer from becoming a heavy user,” said Pacula. 

5. Don’t use the terms “abuse” or “dependence” when reporting on addiction. Instead, use the phrase “use disorder.” Addiction medicine specialists stopped using the terms “abuse” and “dependence” for two reasons, said Zaman. First, they realized that there was a lot of overlap between patients who were diagnosed with abuse versus dependence. Second, there was stigma attached to those labels. So the Diagnostic and Statistical Manual of Mental Disorders, 5th Edition, or DSM-5 — a manual of all psychiatric diagnoses — uses the term “use disorder.” The severity of the diagnoses is then qualified as mild, moderate or severe. 

What about “addiction”? Zaman said it’s acceptable to use in news reports, even though it’s a colloquial term and not a medical diagnosis. And it’s a broader term, because people can be addicted to more than just substances, including gambling, internet gaming, etc.

The AP stylebook says that “addiction” is a preferred term and “substance use disorder” can be used in quotations or scientific context. It advises against using the terms “abuse” or “problem” and favors the term “use.” Avoid the terms “addict,” “user,” and “abuser.”

6. Be aware of your own biases and leave them out of your marijuana coverage. “Some people may know someone who is using [cannabis] to good effects. Others may have known someone who used it to bad effect or had other personal experiences,” said Zaman. “But I think we need to step back and look at the data, like really dispassionately look at the data. And I think that is kind of what’s missing during some heated discussions around cannabis.”

7. Stress the scientific evidence. “Regardless of whether we’re progressive or liberal or conservative, or whatever part of the spectrum, people should go by the scientific evidence,” said Zaman. “I think the issue is getting politicized and sometimes distracting  from the evidence. What about kids getting ahold of these products? What about adults who have addictions or have psychosis or mental health issues? All of that is being completely glossed over by a belief that A. — this is progressive politics and you better get on this side if you’re progressive — and B. — dollars, dollars, dollars, by which I mean the tax revenue and other financial aspects of the cannabis industry.”

More research studies

“Association of Racial Disparity of Cannabis Possession Arrests Among Adults and Youths With Statewide Cannabis Decriminalization and Legalization,” by Brynn E. Sheehan, Richard A. Grucza, Andrew D. Plunk, published in JAMA Health Forum in October 2021, uses arrest data from 43 states to compare “preimplementation and postimplementation differences in arrest rates for states with decriminalization, legalization, and no policy changes.” The study finds that overall, states that legalized or decriminalized cannabis saw large decreases in arrests compared with states that had no policy reform. “Because arrest rate reductions were occurring before policy changes in those states, there is no reason to expect cannabis legalization to have as large of an immediate effect in other states. While these results do not unambiguously favor decriminalization nor legalization, increases in arrest rate disparities in states without either policy highlight the need for targeted interventions to address racial injustice,” the authors write.

“The effect of medical cannabis on cognitive functions: a systematic review,” by Anders Wieghorst, Kirsten Kaya Roessler, Oliver Hendricks, and Tonny Elmose Andersen, published in Systematic Reviews in October 2022, is based on the review of 23 studies and finds “the majority of high-quality evidence points in the direction that the negative impact of cannabis-based medicines on cognitive functioning is minor, provided that the doses of THC are low to moderate.” However, longterm use of cannabis-based medicines may see have a negative effect on cognitive functioning, the authors write.

“Cannabis Use Patterns and Related Health Outcomes Among Spanish Speakers in the United States and Internationally,” by Renée Martin-Willett, Elizabeth Zambrano Garza, and L. Cinnamon Bidwella, published in the Yale Journal of Biology and Medicine in September 2022, is based on the survey of 549 Spanish-speaking people. Among them, 294 lived in the U.S., 174 lived abroad and others didn’t report the country of residence. Overall, the majority used marijuana for recreational reasons. But the U.S. group was significantly more likely to use marijuana for recreational and/or medical reasons. This group also smoked or vaporized marijuana significantly more often than those living outside of the U.S. or with an undisclosed location, and was more likely to use it daily. About 14% of all survey respondents said they used medical marijuana for anxiety and depression. The study “reveals that Spanish-speaking communities in the U.S. and internationally have both shared and divergent cannabis use patterns, particularly for smoking or vaporizing, medical use, and perceptions of safety or risks of using cannabis,” the authors write.

Watch the presentations and get the handouts

• “Marijuana and the Developing Brain,” Zaman’s virtual presentation at the National Press Foundation.
• “Cannabis: Health Effects and Regulatory Issues,” a webinar by SciLine.

Source list for this piece

Dr. Tauheed Zaman: assistant professor of psychiatry at UCSF’s Weill Institute for Neurosciences and an addiction psychiatrist at the San Francisco VA Health Care System.

Ziva Cooper, Ph.D.: pharmacologist, director of the UCLA Cannabis Research Initiative and an associate professor in UCLA’s departments of psychiatry and anesthesiology.

Madeline Meier, Ph.D.: associate professor in the department of psychology at Arizona State University and the director of and principal investigator at the Substance Use, Health and Behavior Lab at the university.

Rosalie Liccardo Pacula, Ph.D.: professor and the Elizabeth Garrett Chair in Health Policy, Economics & Law at the University of Southern California’s Sol Price School of Public Policy.

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Over two million U.S. adults with cardiovascular disease have smoked marijuana, and the substance may carry increased cardiovascular risks, new research indicates.

The study informs questions about the health impacts of policy changes on marijuana. Marijuana use remains illegal federally, but is legal medically in 33 states and the District of Columbia and recreationally in 11 states and D.C. It also makes the case for more research on the effects of marijuana, especially among people with heart disease.

The paper was published this week in the Journal of the American College of Cardiology. It combines a review of the research on cardiovascular risks linked to marijuana use with an analysis of national survey data on use of marijuana in the U.S.

Using data collected through the National Health and Nutrition Examination Survey (NHANES) from 2015 to 2016, the researchers estimate that of the 89.6 million adults in the U.S. who had at some point used marijuana, about 2 million of them had cardiovascular disease – including congestive heart failure, coronary heart disease, or a heart attack.

“That’s an incredible number of people, and even since that time, we know that marijuana use has increased dramatically in the United States,” says Ersilia M. DeFilippis, MD, lead author of the paper and cardiology fellow at Columbia University Irving Medical Center.

“What’s more, there may be many people who are at risk for cardiovascular disease but may not be diagnosed,” she adds. “That just highlights how important it is for us to get good data in this area.”

Currently there is a dearth of controlled research on the subject because marijuana remains classified federally as a Schedule I substance, a Drug Enforcement Administration categorization that indicates these substances have “no currently accepted medical use in the United States,” and a high potential for abuse.

“We know from at least epidemiological studies that marijuana use has been associated with a variety of cardiovascular conditions, including abnormal heart rhythms, weakening of the heart muscle, heart attacks, as well as stroke,” DeFilippis says. Her paper highlights a meta-analysis that finds smoking marijuana was one of the top three triggers of heart attack. Another highlighted study finds that among 334 patients younger than 45 who had experienced a stroke, 17% were cannabis users.

“We have data that suggests these associations,” DeFilippis says. “But we really need to have better controlled studies, to be able to better inform people.”

While research on the health effects of marijuana by delivery method — smoking, ingestion, topical application — is also scarce, DeFilippis points out research finds that inhaled marijuana smoke is, chemically, quite similar to tobacco smoke.

“Although the active ingredients of the cannabis plant differ from those of the tobacco plant, each produces about 4,000 chemicals when smoked and these are largely identical,” finds a 2003 study in The BMJ comparing marijuana and tobacco.

“Given how we accept that smoking is a well-known risk factor for cardiovascular disease, what does that mean for marijuana? And how do we counsel patients?” DeFilippis says.

The research review also highlights known interactions between marijuana and heart medications. Statins, for example, which are prescribed to lower cholesterol levels, can be affected by marijuana use. Levels of statins in the blood may increase when used with marijuana because of how the body metabolizes those substances. Levels of blood thinners, which are used to prevent stroke, and beta blockers, which lower blood pressure, can also increase due to marijuana use.

Further, because marijuana’s chemical composition varies between different strains, medication interactions are “unpredictable,” DeFilippis says.

Given that cardiovascular disease is the leading cause of death in the U.S., DeFilippis urges people who have or are at risk for heart disease to talk with their doctors about their marijuana use, whether it’s recreational or medical.

“Hopefully, with more data, we can help to provide more guidelines for doctors,” she says. “But we do know that for people who are using marijuana and on cardiovascular medications, it will be important for cardiologists as well as our pharmacy colleagues to be aware of potential drug interactions in that setting.”

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A recent study challenges the role that legalizing medical marijuana might play in easing the opioid epidemic.

The paper, published in the Proceedings of the National Academy of Sciences in June 2019, indicates that a previously reported relationship between medical marijuana laws and declining opioid overdose deaths has not held up over time.

The paper uses the same research methods as a 2014 study published in JAMA Internal Medicine, which found that states that had legalized medical marijuana during the study period — 1999 to 2010 — had 24.8% lower annual opioid death rates, on average, compared with states that had not legalized medical marijuana.

The authors of the 2014 study found this association by examining opioid overdose death rates by state using data from the U.S. Centers for Disease Control and Prevention. The data included all overdose deaths in which an opioid was involved, including those that involved other drugs such as heroin. The authors used regression analysis to estimate the relationship between states enacting medical cannabis laws and opioid overdose death rates over time.

This new study replicated the original paper’s findings and extended the investigation through 2017, adding 32 states that legalized medical marijuana between 2010 and 2017 to the sample. When the authors examined the relationship over this longer period, they found that the relationship did not hold. In fact, it reversed direction — opioid overdose death rates increased by 22.7%, on average, in states that had legalized medical marijuana.

“To me, as a public health researcher working in drug policy and epidemiology, this idea that medical cannabis is a very important solution to the opioid overdose crisis is really salient,” explains Chelsea Shover, a postdoctoral research fellow in psychiatry at Stanford University who’s the lead author of the 2019 paper. “It’s just a pervasive idea, and it’s one that I, in the past, had found really compelling, even knowing the limitations that the authors of the first paper mentioned.”

The authors of the original study listed the following as limitations:

• The study is ecologic — that is, it’s concerned with trends at the population-level, such as at the level of the state or the country. This means that it does not and cannot account for what is happening at the level of the individual.
• The death certificate data used by the researchers could be inaccurate. Also, states may differ in how they classify opioid overdose deaths.
• Other factors that could explain the association might not have been accounted for in the model.
• The relationship between medical marijuana laws and opioid overdose death rates may change over time.

Despite this, the original article made a big — and lasting — splash. “That research received substantial attention in the scientific literature and popular press and served as a talking point for the cannabis industry and its advocates, despite caveats from the authors and others to exercise caution when using ecological correlations to draw causal, individual-level conclusions,” the authors of the follow-up study write.

In fact, the original article has been cited in over 400 scientific journal articles and 370 news articles.

Its widespread uptake stems from a few factors, Shover suggests. “There are a lot of people who really want this to be true,” she says. “It’s compelling because it just sort of makes sense on its face and it’s easy for people to understand.”

She maintains that there’s a problem with the way the research has been interpreted by academics and the media. Both studies are concerned with ecological-level associations — that is, population-level trends. These bigger picture associations don’t provide information about what’s happening from person to person. For example, the studies don’t shed light on whether, at the individual-level, people are (or aren’t) substituting medical marijuana for opioids.

Shover and her co-authors write in their paper that the relationship the original study found is likely “spurious.”

Chinazo Cunningham, an author on the 2014 paper, disagrees with using the term “spurious” to describe the association between medical marijuana legalization and decreases in opioid overdose mortality.

“To me, the findings are consistent,” Cunningham says. “The opioid epidemic has evolved. And what it was when we were looking at it, is now different,” she explains. Initially, people were overdosing on prescription opioids. In more recent years, they have died after using heroin and synthetic opioids like fentanyl.

“What we know is that medical cannabis helps with pain,” Cunningham continues. “And the prescription opioids were really around pain and pain management. And so as the epidemic has evolved, it’s become more around addiction. And there really are not data to support the use of medical cannabis to treat opioid addiction. I don’t expect that medical cannabis would treat opioid addiction. Ever. So that is really what I think the [original] findings are saying — medical cannabis helps with pain management, and there can be a reduction in opioid use, but it’s not going to treat necessarily addiction.”

However, Cunningham agrees that both studies are limited in that they cannot establish causality: “These studies also have limitations, definitely,” she adds.

Shover maintains that her work is agnostic on the role of marijuana in treating pain. “What does this study mean for how patients and families should treat their pain?” Shover asks. “The answer to that is nothing. It’s a study about policy; it explicitly is talking about population-level effects and not about the individual-level decisions.”

For now, it’s hard to study the individual-level due to federal marijuana policy that prevents national data collection and analysis, Cunningham points out. “The other really important thing here is, why are we talking about this? It’s about the data and the lack of causality. And that is because we can’t study cannabis in the way we want to study it,” she says. “If we could just change our federal policy to match more with what the states are doing, then we could actually do the studies and have the data that can inform this conversation in a much better way.”

But researchers might be able to get closer to understanding the crux of the issue through different kinds of studies, Shover says. To suggest how to understand the individual-level relationship between opioids and medical marijuana, Shover offers the hypothetical example of a study that looks at state-level medical marijuana registry data and corresponding medical records to see if people who had, prior to registering for medical marijuana, been prescribed opioids, were subsequently prescribed fewer opioids after joining the registry in comparison with people who received opioids for similar diagnoses but who hadn’t registered for medical marijuana. For now, Shover says it would be challenging to execute such a study due to issues with accessing the records involved.

Shover continues, “The relationship between two things can be really different on individual levels than on a population level, and so our work is not aimed at patients for making decisions about how to treat their pain. It’s not aimed at voters who are deciding whether to support decriminalization or legalization. It’s aimed at policy makers who are saying, ‘I could either spend my time trying to push for medical cannabis and then feel like I’ve really done something to address the overdose crisis, or I can say okay, medical cannabis is a separate issue, when I’m thinking of strategies about the overdose crisis I should be focusing on stuff we have better evidence for — like Narcan, like making it easier for people to get treatment and reforming incarceration policies to reduce vulnerability to overdose.’”

Lessons for journalists

This tale of two studies is a great example of why it’s important for journalists to stay close to the source material they’re covering — paying careful attention to the question the study is addressing, as well as the limitations of the research — and not extrapolate beyond the researchers’ findings.

Part of this has to do with framing the research accurately from the outset.

“Headlines help you stay in business, right?” Shover asks. “Well, whatever you go into in the actual article is really important. But it is undercut pretty easily by a headline that’s saying something that’s stronger than what the actual study would say.”

For example, these headlines overstate the 2014 study’s findings:

• “Marijuana Legalization Reduces Opioid Use, Studies Show”
• “Studies: Medical Marijuana Helps Ease Painkiller Addiction Crisis”
• “Despite the Skeptics, Legal Marijuana is Having a Positive Impact on the Opioid Crisis.”

Shover says some of the onus is on researchers, who must communicate their findings in a way that’s both accurate and understandable to the lay public.

Cunningham agrees. “I think that often, as researchers, we’re very specific in the ways that we talk about our findings, and not overselling it,” she says “But I think that gets lost by the media often because the media wants headlines.” But it’s not just on the media: “I do think there’s a dual responsibility of the researchers and the journalists,” she adds. “We have to discuss it in a way where the general public can understand the nuance. And I think that’s really a lot of where the challenge lies.”

From her own experience, Shover advises researchers to say yes to every interview. “Getting out in front of it, and being very forthcoming with reporters and being willing to talk to media has been helpful in that the content of the articles I see out there really do seem to capture what we found and to do a good job of communicating to what it does and doesn’t say,” she says.

Part of it, she says, has to do with putting a study into its proper context — as a contribution to a larger body of research, rather than the last word on a topic.

Shover suggests journalists bring in broader research perspectives beyond just the authors of the study on which they’re reporting. “Bring in basic scientists who are doing research on how it [cannabis] affects the brain, and then people who are doing clinical research, and just talking about it from angles and different levels like whenever possible,” she says. “Trying to get those perspectives is really helpful to understanding what you can and can’t learn from an individual study.”

For more on covering academic research responsibly, check out our tips on determining whether a medical study is newsworthy, pointers from scholars for journalists (and vice versa), suggestions for covering viral research and a useful reminder about the dangers of parachuting into and out of academic research papers.

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There is little evidence to suggest that fatal car accidents increase on April 20 (4/20), an annual holiday that celebrates marijuana, according to new research forthcoming in Injury Prevention.

As states across the country move to legalize medical and recreational marijuana, questions about the impacts of these policy changes – including on driving and rates of traffic accidents – are cropping up, said Sam Harper, associate professor of epidemiology at McGill University and one of the study authors.

“There’s a lot of dynamic action happening in the cannabis policy arena,” Harper said.

Prior research has indicated an increase in traffic fatalities on April 20. A research letter published in JAMA Internal Medicine in April 2018 looked at the relationship between April 20 and fatal traffic crashes in the U.S. Researchers looked at data for 25 consecutive years — from 1992 to 2016 – and compared the number of fatal crashes that happened on April 20 after 4:20 pm to the number of crashes that happened in the same time frame on control days — the same day of the week — one week before and one week after April 20.

They found “a 12% increase in the relative risk of a fatal traffic crash after 4:20 pm on April 20 compared with identical time intervals on control days.”

The research letter spurred Harper’s interest. He wanted to build on the research by comparing the impact of 4/20 on fatal traffic accidents with other risky days.

“We were motivated to look at this in more detail and see what we could find if we did a little bit more testing,” he explained, adding that there is significant day-to-day variation in fatal traffic accidents.

So Harper and co-author Adam Palayew expanded the analysis. In addition to comparing fatal traffic accidents on April 20 with single control days before and after the holiday, they looked at data for control days two weeks before and after. They also compared the number of fatal traffic accidents on April 20 to other known risky traffic days, such as the Fourth of July and Labor Day. Additionally, they analyzed the variation in fatal traffic accidents for every day of the year, “to put 4/20 in the context of other daily variations in traffic crashes,” Harper explained.

The key takeaway? “There is very little evidence that the [4/20] effect was observable over time,” Harper said.

“When we decided to include two control days on either side of April the twentieth, we found a much more diminished effect,” Harper explained.

Further, when the authors compared fatal accidents on April 20 with every other day of the year, it did not stand out relative to the average variation in traffic crashes.

“This is not because daily crash rates are too noisy to detect any signal,” the authors write. “On the contrary, we find important, systematic and meaningful variation in the daily number of drivers involved in fatal traffic crashes across the period from 1975 to 2016. We find consistent evidence for increases in the number of drivers involved in fatal crashes on 4 July and the days prior to Labor Day and American Thanksgiving, as well as systematically fewer drivers involved in fatal crashes on Christmas Day and New Year’s Day.”

In other words, the evidence suggests that there are significant variations in fatal traffic crashes associated with some holidays – but not 4/20.

The authors also analyzed the impact of 4/20 over time. The holiday is a recent phenomenon, popularized in the 1990s, so they looked at data going back to 1976. “We also found little variation in the annual impact of 4/20 over time. If recent celebrations of 4/20 were generating excess fatal crashes we would expect to see a greater excess in recent years,” they write.

Harper added that in the analysis, he found over a dozen days “equally as risky” for fatal traffic accidents as 4/20 that were not linked to any celebratory holiday.

“There’s just a lot of noise in these traffic crashes from day-to-day and from week-to-week, and when you look at the bigger picture, the variation that we see on April 20 is consistent with that variation,” he said.

Harper noted a few limitations of the research. First, the traffic accident data did not contain any measurements of impaired driving or marijuana use.

“This is clearly a very population-focused and 1,000-foot view of this problem,” he said. “To really study carefully the impacts of marijuana consumption and impacts on driving, it needs a different kind of study. Our study isn’t about that question, it is just about fatal crashes on 4/20 compared to other days.”

He noted that the analysis was also constrained to only fatal crash data – analyzing injuries, for example, could potentially produce different results.

“This question about impaired driving and marijuana is an important question, and something I think deserves attention,” Harper said.

He suggested that journalists should pay attention to the topic, “but be careful in how it’s reported… especially where there’s not a lot of research on this.”

“Part of the way this kind of science works, there’s not going to be a single definitive study on this –we’re just trying to build on what we know,” he added. “I’d like to see journalists continue to follow up and report on the story and say there’s more research being done.”

As of March 2019, medical marijuana is legal in 34 states and the District of Columbia; recreational marijuana is legal in ten states and D.C. At the federal level, the drug remains illegal.

Want more research? Journalist’s Resource has covered studies on the link between marijuana legalization and impaired driving. We also have research on the health effects of marijuana and CBD.

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Cases of newborn exposure to illicit substances are much less likely to be reported to the Department of Children and Family Services (DCFS) than to the Department of Public Health (DPH) in Illinois, despite regulations that mandate both agencies receive reports, according to a study forthcoming in Child Abuse & Neglect.

In 14 states and the District of Columbia, exposure to illicit substances in utero is considered a form of child abuse or neglect. In May 2018, the issue made national news in a New York Times feature on children affected by the opioid epidemic, which discusses in-depth how various states address this issue and the effects of drug use on newborns and children.

On the federal level, the Child Abuse Prevention and Treatment Act of 1974 makes funding for drug abuse prevention and treatment services contingent on the reporting of all cases of substance-exposed newborns. But on the state level, requirements vary as to what triggers testing and reporting.

This study, led by researchers mostly based out of the University of Illinois, focuses on their home state in part because of the mandatory reporting policies there. Illinois does not have laws that outline which infants should receive testing. Rather, hospitals determine policies individually as to which infants should be screened. For those infants who are screened and test positive for substances, though, the state requires that these cases be reported both to the DPH and DCFS. Reports to the DCFS might then trigger the removal of the infant from the parent or other interventions. In light of these mandatory reporting laws, this study allows the authors to investigate whether these laws are fulfilled in practice and, if not, the factors associated with deviations from the mandate.

This research looks at differences in reporting by race and ethnicity as well as by geography, focusing on the rural-urban divide. This work builds on past research about racial disparities in child welfare. The researchers compared the number of reports filed with the DPH and DCFS in 2012 and analyzed related variables, including the type of substance involved. The authors note that the discretionary nature of Illinois screening practices serves as a limitation of the study.

They found:

• Just over 1 percent of total live births — 1,838 births — resulted in substance exposure reports to the DPH.
• The DCFS received less than one-quarter of this number of reports — 459 in total. The authors write that this “suggests that social services referrals are more conservatively approached than reports to public health agencies.”
• Over 75 percent of DCFS reports were believed to have credible claims for maltreatment.
• Over 50 percent of the DPH’s reports involved cannabinoids; this was the most common substance involved for white, black and Hispanic infants. (In Illinois, infant marijuana exposure is not considered maltreatment according to DCFS policy, though state statute contradicts this policy. Even in states where marijuana is legal, positive infant screens for THC can trigger the notification of child protective services.)
• White infants had more DPH reports for opioids than cocaine; the reverse was true for black infants. Hispanic infants had slightly more reports for opioids than cocaine.
• Compared to the DPH data, which had roughly equal reports for black and white infants, more white infants than black infants were reported to DCFS, and more of these reports involving white infants indicated credible evidence of maltreatment. The researchers suggest this might be because of the substances involved, as black infants more commonly were reported for cannabinoids, whereas white infants had comparatively more reports of opioids and cocaine.
• The authors suggest the gap in reports between the DPH and the DCFS might be explained partially by the fact that infants might test positive for illicit substances as a result of their mothers’ addiction treatment (e.g., methadone maintenance therapy). Still, they note, this violates the law, which requires a DCFS report for all positive drug tests.
• The DPH and DCFS both received the most reports from rural regions as compared to urban and suburban areas. However, DCFS reports for infants from rural areas were less likely to be categorized as credible claims for maltreatment than for those from urban areas.

The authors conclude that future research might examine the gap between DPH and DCFS reporting. They write, “Variations in the legal architecture both at the interstate and intrastate levels allow for developing of effective policy, but once identified, regulations should be clearly implemented and reinforced to maximize public health.” They suggest state attorneys review “whether DCFS is appropriately executing its regulatory powers,” and possibly amending state laws accordingly. They also suggest that clinicians consider creating statewide protocols to address discrepancies in testing and reporting infant exposure to illicit substances.

Looking for more on drug use and policy in the U.S.? Journalist’s Resource has covered the narrowing race gap in prescription opioid use, safe injection sites’ role as a path to treatment and how to write about fentanyl and synthetic opioids.

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As more states legalize both medical and recreational marijuana, products containing extracts from the plant are appearing on shelves around the country too. Cannabidiol, commonly abbreviated as CBD, is one such compound that’s now available in various formulations at smoke shops, health food stores and dispensaries.

Though CBD is extracted from cannabis, unlike another cannabinoid, THC, it does not have psychoactive properties. So why is this compound that doesn’t provide a high suddenly so trendy? It’s all about the number of therapeutic effects associated with the substance. The evidence is somewhat mixed, but researchers have explored and are continuing to investigate some of the claims tied to the compound.

One application of cannabidiol is in the treatment of epilepsy. A 2018 study published in Epilepsy & Behavior looked at a group of 108 youth epilepsy patients who used CBD oil. The study finds that 39 percent of the children had over a 50 percent reduction in seizures. Ten percent of these patients became seizure-free. Though none of the patients were able to wean off other antiepileptic drugs entirely, 22 percent reduced their use of these drugs. The researchers write that the findings indicate CBD is an effective tool in seizure reduction and has few significant side effects.

Another study, published in the Journal of Epilepsy Research in 2017, summarizes three recent placebo-controlled trials for patients with seizures who received a purified CBD product alongside another antiepileptic drug. These studies found that CBD performed better than the placebo with respect to reducing seizure frequency. However, the author writes that the mechanism of action for CBD is unclear; it might work with other drugs to amplify their effects, rather than directly reduce seizures on its own.

A 2014 review of cannabidiol’s potential therapeutic role in epilepsy and other neuropsychiatric disorders similarly presents reports of the efficacy of the compound for these conditions, though it points out that mechanisms of action are not known and data from double-blind, randomized, controlled studies is lacking.

More rigorous studies are coming out — a double-blind, randomized, controlled clinical trial examining the role of cannabidiol as an additional therapy to treat schizophrenia published March 2018  finds that the experimental group had lower levels of psychotic symptoms than the placebo group. The experimental group also were more likely to be rated as improved and “not severely unwell,” by their doctors. Additional studies support the finding that CBD might possess antipsychotic effects, though a review published in JAMA in 2015 indicates that two studies evaluating CBD in treatment of psychosis found no difference between the experimental and control groups.

Some think the compound might have anti-anxiety effects. Scholars at the University of Sao Paolo summarize a number of human and animal studies, conclude that the compound “promotes antianxiety effects in humans,” and propose a few potential pharmacological mechanisms through which it might work. Individual studies examine the effects of the substance in patients with social anxiety disorder, fear of public speaking and paranoia, generally finding beneficial effects, though the studies all have relatively small sample sizes.

A new paper released ahead of print in Neuropsychopharmacology indicates another potential use for CBD: treating drug addiction. The study, conducted in rats, looked at the “anti-relapse” potential of CBD. The rats, who had histories of consuming alcohol or cocaine, received CBD for a week. Researchers find that “CBD attenuated context- and stress-induced drug seeking without tolerance, sedative effects, or interference with normal motivated behavior.” While this study occurred in an animal model, a small study in humans finds that CBD treatment reduced the number of cigarettes smoked by people who wanted to quit as compared with those who received a placebo. A review of research examining CBD as a treatment for addiction highlights a handful of studies that looked at effects on humans and animals; the findings were mixed. For example, studies of CBD use and cannabis addiction are quite preliminary.

CBD also has anti-inflammatory properties, and is used by some to treat pain, both topically and internally. Most studies of cannabidiol and pain management, however, look at the use of CBD in concert with other cannabinoids, such as THC.

Despite the growing popularity and availability of cannabidiol, the compound remains illegal in the eyes of the federal government. Cannabis extracts, including CBD, are classified by the Drug Enforcement Agency as a Schedule I substance. This is the most restricted category of controlled substances, which the agency defines as “drugs with no currently accepted medical use and a high potential for abuse.” However, some states, like Indiana, have passed laws legalizing the substance, indicating that despite mixed evidence as to the compound’s effects and federal guidelines that legislate against it, CBD is here to stay.

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A new working paper from scholars at the University of Connecticut and Georgia State University finds that alcohol sales decreased in states that have legalized medical marijuana since 2006.

As of late 2017, medical marijuana is legal in 29 states and the District of Columbia; recreational marijuana is legal in eight states and D.C. But federally, the drug is illegal.

As voters increasingly move to legalize marijuana, both medically and recreationally, researchers have analyzed outcomes, including changes in crime rates and traffic crashes in the United States.

Another area of research focuses on the relationship between marijuana and other substances. Studies have considered whether marijuana is a complement or substitute for alcohol. If it is a substitute, that means people use marijuana instead of alcohol. If the substances are complementary, one might expect someone who uses marijuana more often to drink more also. Previous findings have been mixed, but this working paper indicates that marijuana is a substitute for alcohol, and not a complement.

The authors looked at monthly purchases of alcoholic beverages in grocery, convenience, drug and “mass distribution” stores in over 2,000 U.S. counties from 2006 to 2015. They compared sales between counties in 14 states that enacted medical marijuana laws within that time period with those that had no change in medical marijuana laws — that is, the states either legalized the substance prior to the study period, or did not legalize it at all. They focused on purchasing habits during the 18 to 24 months before and after medical marijuana laws went into effect.

They found:

• For counties in states that recently enacted medical marijuana laws, monthly alcohol sales decreased by 15 percent compared to control counties. The drop in sales began immediately after laws were implemented and continued throughout the study period.
• Sales of both alcohol in general and beer and wine specifically declined in states with legal medical marijuana.
• The research team also looked at how sales in bordering counties in particular differed. Alcohol sales were 20 percent lower in counties with recently enacted medical marijuana laws than in neighboring counties without such provisions.

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As states relax their medical and recreational marijuana laws, interest in the drug’s health effects has gained momentum in recent years. “It’s high time to address research into medical marijuana,” Senator Orrin Hatch of Utah, a long-time prohibitionist, said in a September 2017 statement that surprised many. “To be blunt, we need to remove the administrative barriers.”

Judging by the available research, ample evidence exists to indicate that marijuana can treat pain, nausea and multiple sclerosis. It can also harm lungs and the developing adolescent brain. Under certain circumstances, it can be addictive and increase the likelihood of auto accidents, low birth weight and, in cases of heavy use, schizophrenia.

One path of inquiry is the role played by the dozens of natural compounds found in the cannabis plant. Most famous is delta-9 tetrahydrocannabinol (THC) – the stuff that gets you high. THC content has climbed in the past 20 years, from about 4 percent to 12 percent, as growers select strains for THC potency. At the same time, the levels of cannabidiol (CBD), a non-psychoactive compound, has fallen. Yet researchers have observed that CBD can mitigate some of the disagreeable effects of THC, such as paranoia and psychotic symptoms.

A new paper looks into how the changing THC-CBD ratio may be having long-term neurological impacts on young marijuana users.

An academic study worth reading: “Chronic Adolescent Delta-9-Tetrahydrocannabinol Treatment of Male Mice Leads to Long-Term Cognitive and Behavioral Dysfunction, Which Are Prevented by Concurrent Cannabidiol Treatment,” in Cannabis and Cannabinoid Research, 2017.

A team of Indiana University researchers injected 221 male mice – both adolescents and adults – with THC, CBD, and a combination of THC and CBD for 20 days. For five days, starting 24 hours after the latest injection, and again after the mice had been drug-free for six weeks, the team subjected the mice to a battery of behavioral tests: did they recognize objects, did they shred wood chips as normal mice are prone to do, did they bury marbles? The tests assessed anxiety, memory and other traits common in schizophrenia.

Though the mice were all males, the authors believe they are representative: “Based on the rat literature, it is likely that treatment of female mice will also lead to persistent behavioral abnormalities.”

Key takeaways:

• Exposure to THC significantly decreased the adolescent and adult mice’s ability to recognize familiar objects.
• In adults, but not in adolescents, this impairment disappeared after several weeks.
• It appears “THC exposure during adolescence can lead to enduring cognitive impairment that is absent if THC is given during adulthood.”
• Exposure to THC with CBD “completely abolished the deleterious consequences of THC” for both groups of mice.
• CBD alone was found to have no effect on the behavioral tests.
• In an anxiety test after six weeks of clean living, the mice exposed to THC and CBD showed less anxiety than the mice exposed only to THC.
• The results suggest “that higher CBD content in cannabis reduces risk for psychotic disorders.”

Other resources:

See our extensive 2017 roundup on the little-known health effects of marijuana. We have also reviewed literature on how crime and drunk driving tend to fall after marijuana legalization and on the potential tax revenue from legal weed.

The National Institute on Drug Abuse regularly updates its fact sheet on marijuana. The Department of Health and Human Services publishes figures on marijuana use in the U.S., finding, for example, that 8.9 percent of Americans have used marijuana in the past month.

For Scientific American in 2016, David Downs wrote a history of the federal government’s “war” on marijuana. Downs, the cannabis editor at the San Francisco Chronicle, has also penned a glossary of marijuana terminology.

Research on the mitigating effect of CBD include this 2010 paper in Neuropsychopharmacology and this 2013 paper in the Journal of Psychopharmacology.

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As marijuana use becomes ever more socially and legally acceptable in the developed world, researchers are scrambling to understand how the plant — more potent today than ever before — impacts our health. Marijuana is now legal in 28 U.S. states for medical use and in eight for recreation. But policy has far outpaced science, with almost every clinical study calling for further inquiry and many researchers complaining their work is stymied by federal regulations, which still treat cannabis as an illegal substance.

Judging by the available research, ample evidence exists to say that marijuana can treat pain, nausea and multiple sclerosis. It can harm lungs and the developing adolescent brain. Under certain circumstances, it can be addictive and increase the likelihood of auto accidents, low birth weight and, in cases of heavy use, schizophrenia.

The open questions about marijuana and its derivatives are far more numerous. How do benefits balance against side effects? How well can these substances treat seizures? How exactly do they affect the brain? How dangerous are the barely regulated chemicals used in processing weed for commercial use, like butane, pesticides and food additives? What other regulatory loopholes could lead to dangerous effects on consumers?

Without more rigorous study, these questions will remain unanswered and new ones will crop up, leaving policymakers and citizens to argue based on piecemeal research and personal convictions instead of adequate empirical data.

What’s in it and how it’s used

Cannabis has dozens of chemical compounds unique to the plant, known as cannabinoids. The one most famous for the high it gives is tetrahydrocannabinol (THC). But another one, cannabidiol (CBD), is largely non-psychoactive and is often the focus of research on marijuana’s medicinal properties: It may lessen the frequency and intensity of seizures and may even improve cognitive function in adults. Medical marijuana is generally higher in CBD. Both THC and CBD are present in the cannabis plant as inactive acids. Heating — whether by smoking, vaporizing, baking, infusion or other methods — transforms them into active compounds.

What we know

A January 2017 report by the National Academies of Sciences, Engineering, and Medicine reviews most of the known research published since 1999 about marijuana and its impacts on health, making for one of the most comprehensive reads available. “The Health Effects of Cannabis and Cannabinoids” draws almost 100 conclusions, arguing that enough evidence exists to declare that marijuana can be used to treat pain, chemotherapy-induced nausea, and multiple sclerosis.

The report finds substantial evidence that marijuana use may: worsen respiratory function and cause bronchitis (when smoked); increase the likelihood of car accidents; and cause heavy users to develop schizophrenia. It also shows that males who both smoke cigarettes and use marijuana are more likely to develop an addiction to weed than either females or those who don’t smoke cigarettes. Starting to use marijuana before age 16 also raises the risk of addiction. For expectant mothers, considerable evidence suggests that marijuana can negatively impact birthweight.

The report finds moderate evidence: that marijuana use impairs learning, memory and attention, especially in adolescents; that it may improve cognitive performance among some people with certain psychotic disorders; and that it does not worsen schizophrenia. (There is no evidence it can treat the disorder.)

No known association has been found with lung cancer and there is limited evidence that marijuana use increases the risk of heart attacks.

Why we don’t know more 

One problem in compiling the report, and in exploring the health effects of marijuana more generally, is a dearth of studies and funding for research because of federal regulations, said the lead author, Marie McCormick, during a March 2017 event at Harvard’s T.H. Chan School of Public Health.

For one thing, researchers complain about their limited legal access to real weed, the kind people outside of labs use: “It is often difficult for researchers to gain access to the quantity, quality, and type of cannabis product necessary to address specific research questions on the health effects of cannabis use,” the National Academies report declares.

The Drug Enforcement Agency (DEA) classifies marijuana as a Schedule I narcotic. By definition, that means, like heroin, it is highly prone to abuse and has no medical purpose — a rating that Scientific American has called “highly controversial and dubious.” So researchers cannot simply use what they might buy on a street corner or even at a pot shop in states where it is legal under local laws.

The plant clinical researchers do use comes from a farm at the University of Mississippi that the National Institute on Drug Abuse (NIDA) licenses to grow marijuana for research purposes. But scientists complain that what they receive is far less potent than marijuana consumed by the public and even looks like an entirely different plant. The result, The Washington Post declared in 2017, is “akin to investigating the effects of bourbon by giving people Bud Light.”

In August 2016, the DEA announced it would loosen control over the cultivation of government marijuana, though it remains unclear when the changes will go into effect.

Other difficulties studying the effects of marijuana relate to metrics. There is no standard definition of what constitutes frequent use, moderate use or low use, noted Staci Gruber of McLean Hospital at the Harvard event. Researchers have yet to look closely at the effects of marijuana use on those who smoke or eat it once or twice a month. Federal health surveys, moreover, do not ask detailed questions of users.

Kids and pot

One question that has loomed large as more places have legalized marijuana use is, “How bad is it for children?”

Two recent studies observe that regular marijuana use is likely much worse for children before age 16 than it is for adults. A 2015 study in Developmental Cognitive Neuroscience found that kids who start using marijuana before age 16 may have lower cognitive function than people who start using later: “Given that the brain undergoes significant development during adolescence and emerging adulthood and that the frontal cortex is among the last of the brain regions to mature, it is perhaps not surprising that individuals with earlier exposure to [marijuana] have difficulty with tasks requiring frontal/executive function.” A 2014 study in Psychopharmacology also found a correlation between smoking marijuana and impulsive behavior, especially among those who begin regular use before they turn 16.

Marijuana bred for high levels of THC often has less CBD. A 2017 study found CBD may act as a safety mechanism, especially among adolescents.

Other research includes studies on addiction, IQ and the links between legalization and usage:

• One 2017 review in The Lancet notes that while about 1 in 11 people who use marijuana will develop a dependence, that number almost doubles among people who started as adolescents.
• A 2011 study of twins — where one uses pot and one does not — finds no evidence to associate the drug with a lower IQ, though it calls for more research.
• A 2016 study in Drug and Alcohol Dependence analyzes the design of medical marijuana laws and use by adolescents. Looking at 45 states, it finds slightly higher use of marijuana among teenagers in states where medical marijuana is legal (22.7 percent in the previous 30 days) compared to states where it is not (19.8 percent). But after adjusting for demographics and other factors, the authors discover a small decline in adolescent use in those states where medical marijuana is legal.
• Research in Washington and Colorado before and after recreational marijuana was legalized in both states in 2012 found perceptions of its harmfulness fell among youth in Washington but not in Colorado, where medical marijuana had already been well-established. Eighth- and 10^th-grade students in Washington increased their usage over the same period; youth marijuana consumption in Colorado did not appear to change, the authors report in JAMA Pediatrics.

The Canadian Pediatric Society in 2016 released a position statement recommending that Ottawa — where full recreational legalization is being considered — take a number of steps to keep marijuana out of the hands of anyone younger than 18 and regulate the amount of THC in legal marijuana products.

“Dang, that’s strong!”

It’s not your parents’ grass anymore: The marijuana available today is many times more potent than it was in the days of “Reefer Madness” or Woodstock. In 2015, the American Chemical Society reported that THC content in some marijuana strains had roughly tripled in three decades.

One of the most potent products on the market is butane hash oil, sometimes known as marijuana wax. Used in increasingly popular “vape pens” and in the production of edibles, it is made by passing butane (a liver-damaging, explosive and all-around dangerous hydrocarbon gas) through marijuana buds to make a viscous liquid and then evaporating off some of the butane. It is illegal in many states. Not only is the production process dangerous, but smoking “wax made with butane leaves small molecules that adhere to the lungs and creates a black spot much like miners’ lung,” says a handout from the Department of Health and Human Services.

Medical marijuana

With medical marijuana now available in more than half of U.S. states and a growing number of countries, the plant is being used to treat all sorts of ailments including pain and chemotherapy side-effects such as nausea, loss of appetite, and insomnia (even as doctors complain they lack dosing guidelines). Each of these uses is addressed (and generally endorsed) in the 2017 National Academies report.

A major area of study is the use of medical marijuana in treating epileptic seizures, discussed separately below. Other research has explored its effects on cognitive function, on the use of opiates and on the use of recreational marijuana:

• One 2016 study in Frontiers in Pharmacology finds signs that medical marijuana may help improve cognitive function in adults. The researchers suspect this is because some medical marijuana products contain higher amounts of CBD and other cannabinoids than does recreational marijuana, “which may mitigate the adverse effects of THC on cognitive performance.”
• Some scholars see a decline in the use and abuse of opiates by cannabis users, though the National Academies report uncovers no evidence to support or refute this finding.
• Writing in JAMA Internal Medicine in 2014, Marcus Bachhuber of the Philadelphia Veterans Affairs Medical Center and his colleagues find “medical cannabis laws are associated with significantly lower state-level opioid overdose mortality rates.” Patients seem to be using marijuana as an opioid substitute; marijuana is far less addictive and dangerous than drugs derived from the opium poppy. A 2016 study by Columbia University researchers confirms those findings and observes that states with medical-marijuana laws have fewer opioid-related car accidents.
• A 2015 study sees an association between medical marijuana and the lower use of addictive opioids as pain medication; it also reports fewer opioid-related deaths. At the same time, the paper finds a correlation between the availability of medical marijuana and higher rates of recreational marijuana use.

A 2017 study in Drug and Alcohol Dependence finds no indication that CBD, the “medical” cannabinoid, might be addictive.

Treating epilepsy

A fast-growing body of research suggests that CBD — now sometimes called Charlotte’s Web after a CBD-based medicine that reportedly helped a severely ill child — might alleviate treatment-resistant seizures among epilepsy patients. In 2013 the Food and Drug Administration (FDA) allowed tests of Epidiolex, a CBD oil concentrate developed by GW Pharmaceuticals, which is not yet commercially available.

In 2016, the American Epilepsy Society (AES) called on the federal government to support further research into the use of marijuana to treat the neurological disorder. “Robust scientific evidence for the use of marijuana is limited. The lack of information does not mean that marijuana is ineffective for epilepsy. It merely means that we do not know if marijuana is a safe and effective treatment for epilepsy, which is why it should be studied using the well-founded research methods that all other effective treatments for epilepsy have undergone,” the AES statement says.

It also calls on the DEA to review its classification of marijuana as a Schedule I drug: “AES’s call for rescheduling is not an endorsement of the legalization of marijuana, but is a recognition that the current restrictions on the use of medical marijuana for research continue to stand in the way of scientifically rigorous research into the development of cannabinoid-based treatments.”

A 2016 study of CBD in Lancet Neurology finds a 36.5 percent decline in monthly seizures among 162 patients suffering severe, childhood-onset, treatment-resistant epilepsy. The trial was open, meaning patients knew what they were receiving, which is not a preferred way to do medical research; the authors call for randomized controlled trials. Besides the decline in seizures, they find side effects including fatigue, diarrhea, decreased appetite and convulsions.

A number of recent studies — such as this 2017 paper in Epilepsy Behavior and this 2014 paper in Epilepsia – summarize the research and anecdotal evidence that CBD can help control epileptic seizures. They both call for randomized, controlled research trials that are double-blind – i.e., where neither the patients nor the doctors know who is receiving the drug and who is receiving a placebo.

The National Academies report takes a dimmer view of the available clinical data, noting that it consists “solely of uncontrolled case series, which do not provide high-quality evidence of efficacy.” It acknowledges the need for more research into CBD’s potential effect on neurological disorders such as epilepsy and seizures, but concludes that “there is insufficient evidence to support or refute the conclusion that cannabinoids are an effective treatment for epilepsy.”

Regulations, pesticides, food production

Some of the biggest holes in research concern the production of marijuana and its derivatives, including the use of pesticides and the preparation of edibles. Like other deficits in research they stem in part from the disconnect between federal and state laws on marijuana.

In agriculture, pesticides are usually regulated by federal bodies such as the Environmental Protection Agency and approved for specific crops after the pesticide manufacturer pays for testing that the EPA deems reliable. But because the EPA is a federal agency, it will not label a chemical safe for marijuana. So regulation is handled by individual states, which often lack the capacity to investigate problematic pesticides. State governments “have never been made to play the detective role in this,” Andrew Freedman, the former director of the Office of Marijuana Coordination for the state of Colorado, tells Journalist’s Resource.

States where marijuana is legal have been known to recall batches believed to have been exposed to unapproved pesticides such as the insecticides imidacloprid or pyrethrin. (Some states have websites with regulatory information, including California, Colorado and Washington.) Some researchers, meanwhile, express concern about lobbying by the chemical industry to weaken pesticide regulations. Very little has been published about the effects of marijuana pesticides on human health.

Another area in need of study is the production of edibles. The FDA has not approved any product containing CBD as a dietary supplement, but, at the time of writing, has not aggressively enforced federal laws that the FDA interprets to ban marijuana compounds in food.

Marijuana marketing is another topic worthy of greater scrutiny. A 2015 commentary in The New England Journal of Medicine sounds the alarm about the popularity of edible snacks containing THC that are “packaged to closely mimic popular candies and other sweets.” Citing the risk of consumption by children, the authors, two researchers at Stanford, call on the federal government and the courts to regulate the sale of edibles.

Other resources

The number of American cannabis users is rising. According to an August 2016 Gallup Poll, 13 percent of Americans say they use the drug, up from 7 percent in 2007. Slightly older data from the National Survey on Drug Use and Health, published by the U.S. Department of Health and Human Services, say over 22 million Americans aged 12 or older have used marijuana in the past month. That is 8.4 percent of the population.

CannabisWire.com, The Cannabist, and High Times magazine are among the news outlets that cover the growing legal marijuana business. Pot beats and pot critics are increasingly common at traditional newspapers.

For Scientific American in 2016, David Downs wrote a history of the federal government’s “war” on marijuana. Downs, the cannabis editor at the San Francisco Chronicle, has also penned a glossary of marijuana terminology.

Journalist’s Resource has reviewed literature on how crime and drunk driving tend to fall after marijuana legalization. We also have looked at potential tax revenue from legal weed.

The National Institute on Drug Abuse regularly updates its fact sheet on marijuana.

Citations

• Atakan, Zerrin. “Cannabis, a Complex Plant: Different Compounds and Different Effects on Individuals.” Therapeutic Advances in Psychopharmacology, 2012. DOI: 10.1177/2045125312457586.
• Babalonis, Shanna; et al. “Oral Cannabidiol Does Not Produce a Signal for Abuse Liability in Frequent Marijuana Smokers.” Drug and Alcohol Dependence, 2016. DOI: 10.1016/j.drugalcdep.2016.11.030.
• Bachhuber, Marcus A.; et al. “Medical Cannabis Laws and Opioid Analgesic Overdose Mortality in the United States, 1999-2010.” JAMA Internal Medicine, 2014. DOI: 10.1001/jamainternmed.2014.4005.
• Cerdá, Magdalena; et al. “Association of State Recreational Marijuana Laws With Adolescent Marijuana Use.” JAMA Pediatrics, 2017. DOI: 10.1001/jamapediatrics.2016.3624.
• Devinsky, Orrin; et al. “Cannabidiol: Pharmacology and Potential Therapeutic Role in Epilepsy and Other Neuropsychiatric Disorders.” Epilepsia, 2014. DOI: 10.1111/epi.12631.
• Devinsky, Orrin; et al. “Cannabidiol in Patients with Treatment-Resistant Epilepsy: An Open-Label Interventional Trial.” The Lancet: Neurology, 2016. DOI: 10.1016/S1474-4422(15)00379-8.
• Englund, Amir; et al. “Can We Make Cannabis Safer?” The Lancet, 2017. DOI: 10.1016/S2215-0366(17)30075-5.
• Gruber, S.A.; et al. “Worth the Wait: Effects of Age of Onset of Marijuana Use on White Matter and Impulsivity.” Psychopharmacology, 2014. DOI: 10.1007/s00213-013-3326-z.
• Gruber, Staci A.; et al. “Splendor in the Grass? A Pilot Study Assessing the Impact of Medical Marijuana on Executive Function.” Frontiers in Pharmacology, 2016. DOI: 10.3389/fphar.2016.00355.
• Jackson, Nicholas J. “Impact of Adolescent Marijuana Use on Intelligence: Results from Two Longitudinal Twin Studies.” Proceedings of the National Academy of Sciences, 2016. DOI: 10.1073/pnas.1516648113.
• Johnson, Julie; Hodgkin, Dominic; Harris, Sion Kim. “The Design of Medical Marijuana Laws and Adolescent Use and Heavy Use of Marijuana: Analysis of 45 States from 1991 to 2011.” Drug and Alcohol Dependence, 2017. DOI: 10.1016/j.drugalcdep.2016.10.028.
• Kim, June H.; et al. “State Medical Marijuana Laws and the Prevalence of Opioids Detected Among Fatally Injured Drivers.” American Journal of Public Health, 2016. DOI: 10.2105/AJPH.2016.303426.
• Kreslake, Jennifer M.; et al. “Tobacco Industry Control of Menthol in Cigarettes and Targeting of Adolescents and Young Adults.” American Journal of Public Health, 2008. DOI: 10.2105/AJPH.2007.125542.
• Lopez-Quintero, C; et al. “Probability and Predictors of Transition from First Use to Dependence on Nicotine, Alcohol, Cannabis, and Cocaine: Results of the National Epidemiologic Survey on Alcohol and Related Conditions.” Drug and Alcohol Dependence, 2011. DOI: 10.1016/j.drugalcdep.2010.11.004.
• MacCoun, Robert J.; Mello, Michelle M. “Half-Baked — The Retail Promotion of Marijuana Edibles.” New England Journal of Medicine, 2015. DOI: 10.1056/NEJMp1416014.
• McCormick, Marie; et al. “The Health Effects of Cannabis and Cannabinoids.” National Academies of Sciences, Engineering, and Medicine, 2017. DOI: 17226/24625.
• McLaren, Jennifer. “Cannabis Potency and Contamination: A Review of the Literature.” Addiction, 2008. DOI: 10.1111/j.1360-0443.2008.02230.x.
• O’Connell, Brooke K.; Gloss, David; Devinsky, Orrin. “Cannabinoids in Treatment-Resistant Epilepsy: A Review.” Epilepsy and Behavior, 2017. DOI: 10.1016/j.yebeh.2016.11.012.
• Powell, David; Pacula, Rosalie Liccardo; Jacobson, Mireille. “Do Medical Marijuana Laws Reduce Addiction and Deaths Related to Pain Killers?” RAND Corporation, 2015. DOI: 10.7249/WR1130.
• Russo, Ethan B. “History of Cannabis and Its Preparations in Saga, Science, and Sobriquet.” Chemistry and Biodiversity, 2007. DOI: 10.1002/cbdv.200790144.
• Sagar, K.A.; et al. “The Impact of Initiation: Early Onset Marijuana Smokers Demonstrate Altered Stroop Performance and Brain Activation.” Developmental Cognitive Neuroscience, 2015. DOI: 10.1016/j.dcn.2015.03.003.
• Schauer, Gillian L.; et al. “Trends in and Characteristics of Marijuana and Menthol Cigarette Use Among Current Cigarette Smokers, 2005–2014.” Nicotine and Tobacco Research, 2017. DOI: 10.1093/ntr/ntw394.
• Subritzky, Todd; Lenton, Simon; Pettigrew, Simone. “Legal Cannabis Industry Adopting Strategies of the Tobacco Industry.” Drug and Alcohol Review, 2016. DOI: 10.1111/dar.12459.

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For years, the image of the silly, spaced-out stoner seemed to embody marijuana use in popular culture. But with new, relaxed marijuana policies becoming law in many states, the picture is changing. High-functioning executives, government officials and even grandparents are openly discussing smoking pot.

Still, the question remains: Does marijuana negatively impact intelligence? Researchers have long disagreed. A new study using many years of data tries to settle the debate.

An academic study worth reading: “Examining the Influence of Adolescent Marijuana Use on Adult Intelligence: Further Evidence in the Causation Versus Spuriousness Debate.” In Drug and Alcohol Dependence, 2017.

Study summary: Criminologists Cashen Boccio and Kevin Beaver of Florida State University review the available — and contradictory — research on the relationship between adolescent marijuana use and intelligence. Unsatisfied, and concerned that previous research did not control for enough factors, they examine a large, longitudinal dataset funded for decades by the U.S. government: The National Longitudinal Study of Adolescent to Adult Health. “Add Health”, as the survey is known, began tracking over 20,000 middle school and high school students in 1994-1995 and has followed these students well into adulthood through three subsequent waves (in 1996, 2001-2002 and 2008). It is, say its organizers, “the largest, most comprehensive longitudinal survey of adolescents ever undertaken.”

Add Health studies a number of factors. Boccio and Beaver are interested in verbal intelligence, which is often used as a proxy for overall intelligence, and marijuana use. In order to test the relationship, the researchers examined frequency of use and cumulative use over time (by comparing different waves of the study).

The researchers did not consider respondents who indicated using marijuana during the first wave (when some were as young as 12), so they could focus on those who started using the drug as adolescents. This also allowed them to measure any changes to intelligence between the first wave in 1994-1995 and the third wave in 2001-2002. They control for a number of factors, including socioeconomic status and personality traits.

Key takeaways:

• Trying marijuana was associated with lower intelligence scores.
• There was, however, no clear relationship with the amount of marijuana consumed: “There is no dose-dependent relationship between marijuana use and changes in intelligence scores.”
• Neither personality factors nor socioeconomic status affected these findings.
• Compared with someone who had never tried marijuana, having tried as an adolescent was associated with a 2.098 percentage point decrease in intelligence scores (which the authors call “relatively small”).
• Compared with someone who had never tried marijuana, having tried (for the first time) as a young adult was associated with a 1.06-point decrease in intelligence scores.

Limitations: The authors were unable to measure the effects of marijuana dependence because each wave only recorded 30 days of use. “The findings of this study can only be generalized to low/average levels of marijuana use and not heavy users or individuals who are marijuana dependent,” they write.  They also warn that the findings could be confounded by the abuse of other substances.

Other research:

• We wrote an extensive review of scientific literature on marijuana and health in 2017. We have also reviewed research on marijuana use, crime and distracted driving.
• Is marijuana a gateway drug? A 2017 study in The B.E. Journal of Economic Analysis & Policy suggests it is not.
• Low doses of marijuana may make us relax, while higher doses are associated with stress, a forthcoming study in Drug and Alcohol Dependence indicates.
• Teenagers from upper-middle class suburbia are substantially more likely to abuse alcohol and drugs than the national average and to carry these abusive patterns into adulthood, according to a forthcoming study in Development and Psychopathology. The authors also observe that stricter parenting at age 17 and 18 is associated with lower rates of substance abuse in adulthood.

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The issue: Since Colorado became the first state to legalize recreational marijuana in 2012, initiatives to bring pot out of the shadows have spread rapidly across the United States. Almost half of states now sanction marijuana for medical purposes – even though it remains illegal under federal law. American public opinion also has shifted toward acceptance. In 1969, according to the Pew Research Center, 84 percent of Americans thought the drug should be illegal; by 2015, that number had fallen to 44 percent.

Legalization raises a number of questions with policy implications. For example, how can it be taxed? In 2015, Colorado raised $135 million in taxes and fees from legal sales. Another important question: Will states that stop arresting people for selling or having marijuana save money on policing and reduce their incarceration rates? Some 620,000 people were arrested for marijuana possession in 2014, according to the FBI; young minority men were disproportionately targeted. Will more children take to smoking weed? As laws relax and the stigma associated with marijuana recedes, people may use more.

An academic study worth reading: “Marijuana on Main Street? Estimating Demand in Markets with Limited Access,” published in American Economic Review, August 2016.

Study summary: Economists Liana Jacobi of the University of Melbourne and Michelle Sovinsky of the University of Mannheim look at how limited access affects usage rates among Australians of different ages. The Australian data is especially useful because it includes statistics on accessibility and prices. Recreational marijuana is currently illegal in Australia, though some states began introducing medical marijuana laws in 2016. As in America, marijuana is the most commonly used illicit drug in Australia.

The authors look at the role accessibility plays in usage and how tax revenues are affected when marijuana is regulated like alcohol and sold to people above the age of 21. They also examine how taxation can curb use among youth. Jacobi and Sovinsky extrapolate their analysis to include the United States, a country with similar cultural behaviors and economies. 

Findings:

• The U.S. could raise between $4 billion and $12 billion annually by taxing legal marijuana. These numbers are based on a tax levy of about 25 percent, which is what the state of Colorado charges. This rate could maximize state revenues without incentivizing the black market.
• When people have more access to marijuana (through legal and illegal means) more people use it.
• When marijuana is illegal, both access and usage drops as people age. Access is better among the young. Men have better access, and use more, than women. Legalization, therefore, improves access for larger numbers of older people and prompts a larger proportion of older people to begin using.
• Currently, 17 percent of Australians say they do not use cannabis for fear of legal repercussions; 90 percent of those say that access is not the reason.
• If marijuana use was legalized and individuals had easy access to the drug, usage rates would rise by approximately 50 percent in the U.S. If that happened, about 19.4 percent of U.S. adults would use marijuana.
• To prevent teenagers from increasing consumption after marijuana becomes legal for adult use, the price would have to rise fourfold. That is unfeasible because it would encourage a return of the black market. Instead, a tax of 25 percent would stop roughly one-third (34 percent) of potential new teenage users from starting to use marijuana. To stop 40 percent of potential new teenage users, prices would have to almost double. Prices would have to almost triple to cut the number of new teenage users by half.

Other resources:

The number of American cannabis users is rising rapidly. According to an August 2016 Gallup Poll, 13 percent of Americans say they use the drug, up from 7 percent in 2007. Slightly older data from The National Survey on Drug Use and Health, published by the U.S. Department of Health and Human Services, say over 22 million Americans aged 12 or older have used marijuana in the past month. That is 8.4 percent of the population.

The National Institutes of Health (NIH) publishes research on the health impact of cannabis consumption.

Legalization in Colorado has been a closely watched experiment. The state’s Department of Revenue publishes its tax receipts from marijuana sales on a monthly basis.

The American Civil Liberties Union reports that black people are almost four times more likely to be arrested for marijuana possession than whites, even though both groups use the drug at roughly the same rate.

There are a number of advocacy groups working both sides of the legalization debate, including some funded by the cannabis industry. The Marijuana Policy Project lobbies for legalization and regulation. It updates a database of ballot initiatives around the country. Smart Approaches to Marijuana is an anti-legalization lobby group.

CannabisWire.com and High Times magazine are among the news outlets that cover the growing legal marijuana business.

LEAP – Law Enforcement Against Prohibition – is a body of police and other law enforcement officials promoting legalization. It argues that prohibition has failed and distracts police from fulfilling their duties to the public.

Professor Mark Kleiman of New York University has written extensively about criminal justice and marijuana.

Other research:

A 2016 paper in Preventative Medicine analyzes news coverage of recreational marijuana policy and reports that opponents of legalization most often argue about public health concerns, but that stories about opposition rarely mention public health research. Proponents of legalization most often use arguments on reduced criminal justice expenditures and increased tax revenues.

A 2015 study published in Alcoholism: Clinical and Experimental Research explores how marijuana legalization impacts alcohol consumption.

A 2015 study by the RAND BING Center for Health Economics sees an association between medical marijuana and the lower use of addictive opioids as pain medication; it also reports fewer opioid-related deaths. At the same time, the paper finds a correlation between the availability of medical marijuana and higher rates of recreational marijuana use.

There is a growing debate between federalism and states’ rights when it comes to marijuana legalization. The federal government continues to classify cannabis as a Schedule I drug, like heroin and cocaine. That means cultivators, distributors and dispensaries that sell marijuana legally under state laws have severely restricted access to the banking system, which is more often regulated at a federal level. On these restrictions, see the 2015 article “Cooperative Federalism and Marijuana Regulation” published in the UCLA Law Review and the 2014 article “Banks, Marijuana, and Federalism” in Case Western Reserve Law Review.

Keywords: weed, pot, dope, edibles, hemp, Reefer Madness, THC, cannabidiol, CBD, Charlotte’s Web

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The decisions by Colorado and Washington State to legalize the sale of marijuana have set off a wave of speculation about the local, national and international implications. Experts note that even the Netherlands, long known for its permissive culture of marijuana use, has not gone as far as these two states, which have opened up commercial sales to the market with relatively little restriction. These changes are substantial in many ways: Research has suggested that in 2013 alone, when Washington had just decriminalized marijuana — and before commercial sales were permitted — as much as 225 metric tons of cannabis was consumed there. By comparison, somewhere between 50 and 150 metric tons of marijuana is sold in the Netherlands annually.

Some worry about the effects on young people of widespread commercial availability. “Instead of starting with an approach that lent itself more easily to public health protections,” writes Beau Kilmer of the RAND Corporation, “voters in Colorado and Washington jumped right to a market model similar to alcohol.” While scientific research is advancing our understanding of the health risks of marijuana use, randomized control trials — the gold standard of academic research — have yet to be conducted at a scale that would answer every question and concern.

However things play out in Colorado and Washington, it’s evident that the global status quo on the prohibition of the production and sale of marijuana is becoming more unsettled. The recent legal shifts by the United States and Uruguay — it approved the cultivation and sale of marijuana in December 2013 — have been criticized by the United Nations International Narcotics Control Board. Applicable international laws include the 1961 Single Convention on Narcotic Drugs, an amended 1972 version of that convention, and the 1988 United Nations Convention Against Illicit Traffic in Narcotic Drugs and Psychotropic Substances. Nearly all countries are signatories to these conventions and have agreed to punish citizens who violate these principles.

A December 2013 report from RAND, a non-partisan research center, sheds light on how other countries have grappled with marijuana legalization or decriminalization policies. The report, “Multinational Overview of Cannabis Production Regimes” — authored by Kilmer, Kristy Kruithof, Mafalda Pardal, Jonathan P. Caulkins and Jennifer Rubin — looks at case studies in Spain, Belgium and Uruguay, as well as the United States. “While the international treaties related to cannabis have not changed in nearly 25 years, laws and policies pertaining to cannabis have changed in some countries, especially at the state or regional level,” they write. “A number of jurisdictions have reduced their penalties for possessing cannabis for personal use, making the maximum penalty a fine and/or participation in some type of diversion program or community sentence.”

The report’s findings include:

• Uruguay is the example most parallel to the new scenarios in Colorado and Washington: “Under Uruguayan law, consumption and possession ‘of a reasonable amount of drugs’ for personal use is not penalized.” However, Uruguay is the only country to enact such legal changes at the national level. Statements by government officials there about their obligations to international treaties indicate that Uruguay has chosen to “revise” these existing global rules and pursue an “alternative” framework. (The issue of international law is a complex one that hinges on interpretations of federated systems of government, where regional and local changes may occur, versus national policies.)
• Belgium and Spain have so far only permitted distribution through “cannabis clubs.” In Belgium, cannabis production is not allowed by law. However, officials have formally put forward law enforcement guidelines that de-emphasize marijuana possession as a crime; they have given it the “lowest possible priority” in terms of prosecution “for possession of up to three grams of cannabis or one cultivated cannabis plant.” Still, members of marijuana organizations have been involved in litigation in recent years.
• Spain has had a slightly different legal experience: “Following several Supreme Court rulings, the possession and consumption of cannabis is no longer considered a criminal offense, and the jurisprudence in the field has tended to interpret the existing legislation in a way that permits ‘shared consumption’ and cultivation for personal use when grown in a private place. While there is no additional legislation or regulation defining the scale or particulars under which cultivation could be permitted, the Cannabis Social Club (CSC) movement has sought to explore this legal space, reasoning that if one is allowed to cultivate cannabis for personal use and if ‘shared consumption’ is allowed, then one should also be able to do this in a collective manner. In this context, hundreds of CSCs have been established over the past 15 years, but legal uncertainty around the issue of production continues and has led to the seizure of cannabis crops and to the arrest of some CSC members.”
• As for the legal shifts and international treaty obligations of the United States, the authors note: “In the U.S. there has been very little official discussion about how legalizing the recreational cannabis industry in two states and the subsequent federal response fit or fail to fit within the U.N. drug conventions. After the voters passed the propositions, U.S. Attorney General Holder initially stated that he would consider the ‘international obligations’ when crafting a response. However, neither the subsequent memo from U.S. Deputy [Attorney General] Cole, which described the federal position, nor Cole’s official testimony at a Senate Judiciary Committee hearing about cannabis policy in September 2013 mentioned the international conventions.”

The authors also look at places where medical or scientific use is permitted to varying degrees — such countries include Canada, Chile, Czech Republic, France, Israel, Germany, the United Kingdom and Switzerland — or where “proposals for recreational use have been (or will be) submitted,” including in Chile, Denmark, Portugal and Switzerland.

A 2010 RAND report on the Netherlands, “What Can We Learn from the Dutch Cannabis Coffeeshop Experience?” notes that since 1976 the Netherlands has operated under a “formal written policy of non-enforcement for violations involving possession or sale of up to 30 grams of cannabis.” As of 2010, there were about “700 retail cannabis outlets in the Netherlands — about one per 29,000 citizens (one per 3000 in Amsterdam).” The industry “employs 3,400 workers … and the owners have their own union….  They sell somewhere between 50 and 150 metric tons of cannabis at a value of perhaps 300 to 600 million euros a year.”

Keywords: drugs, marijuana

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The U.S. Department of Justice issued a memo on Aug. 29, 2013, advising state attorneys general that it would not try to block laws that allow for some legal medical and recreational marijuana use. In 2012, voters in the states of Washington and Colorado approved the decriminalization of small amounts of recreational marijuana use; 18 other states and Washington, D.C., allow for some medicinal usage. The decision immediately drew strong criticism from a coalition of law enforcement organizations, which sent a letter of complaint to Attorney General Eric Holder.

In that letter, the coalition of sheriffs, police chiefs and other officers involved in drug investigations note that marijuana usage can impair people’s ability to drive automobiles, and asserted that its use is generally associated with crime. For its part, the Department of Justice acknowledges the problems with impaired driving as well as associations with crime and criminal networks, and says curbing these phenomena remains a priority. But the law-enforcement group letter goes even further, claiming that “marijuana’s harmful effects can include episodes of depression, suicidal thoughts, attention deficit issues.” (It should be noted that not all law enforcement officers or groups agree with these critiques.)

Setting aside the questions about criminal or negligent behavior and the merits of medical use, what is the scientific evidence for these general claims about the cognitive effects of pot? Broadly speaking, the medical research literature has noted some problems for heavy users and persons who begin significant use of marijuana at a young age. A 2014 study published in the Journal of Addiction Medicine found troubling evidence of problems with addiction among adolescents (this comes as survey research suggests daily pot use is up among some younger populations such as college students.) But recent medical research has weighed some of the evidence and surfaced further nuances in the conclusions about cognitive effects.

The research in this area is evolving and single studies — even those published in top journals — come under a lot of scrutiny, given the political stakes. For example, a 2012 study published in the Proceedings of the National Academy of Sciences, “Persistent Cannabis Users Show Neuropsychological Decline from Childhood to Midlife,” found evidence that long-term use of marijuana early in life led to declines in IQ scores. But the sample size and other elements were criticized in some quarters, and the authors themselves note several limitations.

For obvious reasons, there have not been large-scale randomized control trials in laboratory conditions — the gold-standard for medical and scientific research — and therefore a great deal of the research on marijuana comes with caveats. In addition, leading experts such as Mark A.R. Kleiman of UCLA acknowledge the public health drawbacks but note that any serious policy analysis must take into account multiple other considerations. In a 2011 review article in the journal Addiction, Kleiman states:

A full analysis of cannabis policy would work forward from (i) formal policies embodied in statutes, regulations and the budgets and administrative rules of public agencies, to (ii) policies-in-practice (e.g. of enforcement) carried out by officials, to (iii) conditions influencing cannabis use (such as price, availability, legal risks faced by users and attitudes), to (iv) use itself, to (v) harms associated with use (vi), harms associated with illicit commerce and (vii) to harms associated with enforcement, including both budget costs and the damage resulting from punishment.

The following is a representative sample of academic studies relating to the cognitive and personal health aspects of the issue:

Depression

A June 2013 metastudy — an examination of prior scholarly research — published in Psychological Medicine analyzed the 14 most rigorous studies available that, combined, looked at results for more than 76,000 subjects. The paper, conducted by a team of researchers at the University of Toronto and several other institutions, represents the “current state of knowledge on this association.” The research accounts for a number of problems that have weakened other single studies, such as small sample sizes or study groups where persons with other mental health problems were over-represented. The 2013 metastudy, titled “The Association between Cannabis Use and Depression: A Systematic Review and Meta-analysis of Longitudinal Studies,” finds: “Cannabis use was associated with a modest increased risk for developing depressive disorders…. [H]eavy cannabis use was associated with a stronger, but still moderate, increased risk for developing depression. These associations … were consistent for cannabis use both in adolescence and in adulthood.”

However, the researchers concede that existing research has not fully accounted for a number of variables — including how cumulative exposure works, and types of marijuana used — and, overall, “results pertaining to increased risk for depression among cannabis users should be regarded with caution.”

It should also be noted that other newer research, such as a 2012 study in the journal BMC Psychiatry, finds no relationship between cannabis and depression, but establishes a link with “psychosis” (although even the psychosis connection remains contested and in need of more research.) A December 2013 study published in Schizophrenia Bulletin finds some connection between heavy marijuana use during teenage years and severe mental illness, though the study’s authors note that more long-term research is needed to definitively confirm the results and establish a firm causal relationship.

Suicide

A 2012 study published in the journal Addictive Behaviors, “Daily Marijuana Use and Suicidality: The Unique Impact of Social Anxiety,” notes that research has demonstrated a “clear relationship” between cannabis and suicide, but medical scientists have established relatively little about the precise connection or exactly why it is such a “risk factor.” That study suggests that certain additional factors, such as underlying levels of social anxiety, are truly what make regular marijuana users more likely to be suicidal. It also suggests the difficulty of separating out marijuana’s exact role in fostering suicidal tendencies. Further, a May 2013 study in the Journal of Health Economics, finds that “using cannabis at least several times a week leads to suicidal ideation in susceptible males. [But] we find that … suicidal ideation does not lead to cannabis use for either males or females.”

Still, as noted in a 2009 research paper in the Journal of Forensic Sciences, an analysis of toxicology reports suggests that victims of suicide are more likely to have used marijuana. However, there is very credible research, such as a 2009 study in the British Journal of Psychiatry, that casts doubt on any direct link between cannabis use and suicide.

Attention deficit issues

If by “attention deficit issues” one means a general diminishing of cognitive functioning, there is medical research that supports the notion that cannabis can negatively affect one’s memory and learning ability both during and after use. However, when researchers speak of a cannabis-attention deficit connection, they frequently refer to the cultural phenomenon — still controversial — of people with ADHD using marijuana to “self-medicate.” It is, in any case, a complicated matter. An August 2013 study published in Psychiatry Research, which examined a relatively small number of subjects (56 men, 20 women), yields interesting findings but also underscores the challenge of proving the exact relationship and disentangling variables: “Significant correlation between greater frequency of marijuana use and increased number of inattentive symptoms was found in men, but not in women with ADHD. Although men with ADHD showed a stronger correlation than women, the correlation coefficients were not significantly different between genders. Previous research suggested that individuals with ADHD may use marijuana to treat their symptoms … and our findings may support this hypothesis in men. Alternatively, increased marijuana use may negatively affect inattention in men, and to a lesser degree in women with ADHD. Clearly, more research is necessary to examine the causal effects of marijuana on ADHD symptoms.”

Any causal connection is also complicated by the fact that people with substance-use disorders in general are more likely to be afflicted with ADHD, and vice versa, as suggested by a 2012 metastudy in the journal Drug and Alcohol Dependence.

Keywords: drugs, cognition

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Marijuana usage in America rose 6.9% between 2009 and 2010, when some 17.4 million Americans reported using the drug. Sixteen states now permit the medical use of marijuana for diseases such as glaucoma and multiple sclerosis, but the drug’s growing popularity is primarily due to more recreational users ages 18 to 34, according to the Substance Abuse and Mental Health Services Administration.

While the dangers of drinking and driving are clear, the perils of operating a vehicle under the influence of marijuana are still being debated; groups such as the National Organization to Reform Marijuana Laws (NORML) claim that while risks do exist, they are minimal. Studies that describe marijuana’s adverse cognitive effects have typically been conducted in labs, not in real-world settings.

A 2011 metastudy from Columbia University published in Epidemiologic Reviews, “Marijuana Use and Motor Vehicle Crashes,” compares nine epidemiological studies from six countries published after 1990 on marijuana use and motor vehicle accidents.

Key study findings include:

• Eight of the nine studies reported a statistically significantly increased risk of crash involvement associated with a driver’s marijuana use prior to operating a vehicle.
• “Drivers who test positive for marijuana or self-report using marijuana use are more than twice as likely as other drivers to be involved in motor vehicles crashes.”
• In a study of more than 64,000 insured U.S. drivers between 1979 and 1985, 31% of drivers involved in a motor vehicle crash reported smoking marijuana prior to the accident.
• The study findings were “generally consistent across … different geographic regions and driver populations, [despite] us[ing] different research design approaches, and [being] based on different methods for measuring marijuana use.”

The authors note that the “crash risk appears to increase progressively with the dose and frequency of marijuana use.”

Tags: cars, drugs, safety, metastudy

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