Cannabis use disorder may increase risk for certain psychiatric illnesses

Pot. Weed. Mary Jane. Dope. Cannabis goes by many names. The drug has had a rocky history in the United States, but today, many states have legalized cannabis use or made it available with a doctor’s prescription.

A research team led by Yale scientists evaluated the relationship between cannabis use traits and psychiatric disorders. Their results, published recently in Nature Mental Health, show that cannabis use disorder places people at increased risk of developing several psychiatric disorders, providing beneficial guidance that public health professionals can use to gauge the potential utility of cannabis for their patients.

“Sometimes in the news, you can read an article that says cannabis can benefit mental health disorders, or it can be used to try to mitigate the effects of some other substance use disorders,” says Marco Galimberti, Ph.D., associate research scientist at Yale School of Medicine (YSM) and first author on the study. “In our study, we show that people who develop cannabis use disorder can actually have a higher risk of developing psychiatric disorders.”

A 2021 report by the National Survey on Drug Use and Health in the United States found that 52.5 million people (aged 12 or older) have used cannabis in their lifetime. And studies have found that an estimated 30% of people who use cannabis have cannabis use disorder, a mental health condition characterized by a problematic pattern of cannabis use that leads to significant impairment or distress.

In the new study, researchers analyzed previously published genome-wide association analyses (GWAS) to examine relationships between cannabis use disorder and psychiatric illness. GWAS datasets are used to identify genetic variations associated with a specific disease or trait by examining millions of genetic markers across the entire genome.

The datasets included in the study addressed cannabis use disorder, cannabis use, and numerous major psychiatric traits. The GWAS datasets informed how genetic variants might relate to disease and the researchers were then able to perform analyses that measured whether and to what degree the genetic risk for one disease or trait affected the genetic risk for another disease or trait.

The researchers uncovered several bidirectional causal relationships, in which not only did having a psychiatric condition put people at greater risk of developing cannabis use disorder, but also having cannabis use disorder put people at greater risk of developing a psychiatric disorder.

Their results supported previous research that identified bidirectional causal relationships between cannabis use disorder and schizophrenia and bipolar disorder. They also, for the first time, established bidirectional relationships between cannabis use disorder and anxiety disorder, major depressive disorder, and post-traumatic stress disorder (PTSD).

“People might suggest cannabis use can be a useful treatment for, say, PTSD, but this analysis indicates otherwise,” says senior author Joel Gelernter, MD, Foundations Fund Professor of Psychiatry and professor of genetics and of neuroscience at YSM.

“We show that over time, cannabis is more likely to cause PTSD than to treat it. When medications are approved for a particular condition, we generally require strong scientific evidence that the treatment works, but clinical trials are lacking for cannabis for many of these traits.”

The results from this study offer a fact-based approach that public health professionals can use to gauge the potential utility or harm of cannabis use by people with certain mental health disorders, say the researchers.

“With medical marijuana becoming increasingly legalized, many clinicians have been willing to prescribe cannabis for a range of disorders,” says Gelernter. “Our study shows that this may not be the best practice. We need randomized clinical trials to show whether cannabis works in order for it to be reasonably considered a medication.”