Cannabis—also known as pot, weed, Mary Jane, or dope—has become increasingly accepted in the U.S., with many states legalizing it for medical or recreational use. But a new study from Yale scientists suggests that regular, heavy cannabis use may come with serious mental health risks.
Published in Nature Mental Health, the study found that people with cannabis use disorder are at higher risk of developing several psychiatric illnesses, including schizophrenia, bipolar disorder, depression, anxiety, and post-traumatic stress disorder (PTSD).
The researchers also discovered that the relationship goes both ways: people with these mental health conditions are also more likely to develop cannabis use disorder.
Cannabis use disorder is a condition where a person struggles to control their cannabis use even when it causes problems in their life. It’s more common than many people realize. According to a 2021 national survey, more than 52 million Americans aged 12 or older have used cannabis, and around 30% of them may develop cannabis use disorder.
Lead researcher Dr. Marco Galimberti and his team at Yale School of Medicine used a type of genetic analysis called genome-wide association studies (GWAS) to look for links between cannabis use and mental illness. GWAS datasets include millions of genetic markers from large populations and are used to identify which genes are associated with certain diseases or traits.
The researchers compared genetic data related to cannabis use disorder with data on several psychiatric conditions. They found strong genetic links suggesting bidirectional causal relationships—meaning that one condition can increase the likelihood of the other.
This confirms earlier research showing connections between cannabis use disorder and schizophrenia or bipolar disorder. But the Yale team also identified new links with anxiety, major depression, and PTSD.
That means using cannabis regularly doesn’t just raise the risk for serious psychotic disorders—it may also make it more likely that someone develops depression, anxiety, or trauma-related conditions.
These findings challenge a growing belief that cannabis might help with mental health issues. “Some people think cannabis could help treat PTSD or other disorders,” says senior author Dr. Joel Gelernter. “But what we found is that cannabis is more likely to cause PTSD than treat it.”
The study warns against prescribing cannabis for mental health conditions without stronger scientific proof. “When a drug is approved for medical use, it usually goes through randomized clinical trials to show that it’s safe and effective,” says Gelernter. “But that’s not the case for cannabis in most situations.”
As more states legalize marijuana and doctors feel pressure to prescribe it for a wide range of conditions, researchers say this study offers critical evidence to guide safer medical decisions. They emphasize that strong clinical trials are needed before cannabis can be considered a proven treatment for mental illness.
In short, while cannabis may help some people in specific cases, frequent use—especially when it turns into cannabis use disorder—can increase the risk of developing serious mental health problems. Public health officials and clinicians should proceed with caution and focus on treatments with clear, evidence-based benefits.
If you care about cannabis, please read studies that what you need to know about cannabis and heart attack, and CBD from cannabis may help inhibit COVID-19 infection.
For more information about cannabis, please see recent studies that medical cannabis could help reduce depression, and results showing this stuff in cannabis may protect aging brain, treat Alzheimer’s.
The research findings can be found in Nature Mental Health.
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