A large review of past studies has found that cannabis products with high levels of THC—the main compound that causes a “high”—may be linked to harmful effects on mental health.
This includes a higher risk for serious conditions like psychosis, schizophrenia, and cannabis use disorder (CUD).
These findings were published in the journal *Annals of Internal Medicine* and add to growing concerns about the mental health risks of using strong cannabis products.
The review was done by researchers from the University of Colorado Anschutz Medical Campus. They looked at 99 studies from around the world, covering over 220,000 people, dating from 1977 to 2023.
Their goal was to see how high-THC cannabis affects mental health. They didn’t just focus on studies that tested cannabis for medical use—they included any research that looked at links between strong cannabis and mental health problems.
In this review, cannabis products were considered “high-concentration” if they contained more than 5 milligrams of THC per serving or more than 10% THC overall. Products labeled as “high-potency concentrate,” “shatter,” or “dab” were also included.
The mental health effects the researchers looked at included anxiety, depression, psychosis, schizophrenia, and addiction to cannabis or other drugs. They divided the effects into three types: short-term (within 12 hours of use), medium-term (after 1 to 2 months of regular use), and long-term (after a year or more of use).
Here’s what they found: In studies not focused on medical benefits, high-THC cannabis was strongly linked to psychosis, schizophrenia, and cannabis use disorder. No studies that tested cannabis for medical reasons found it helpful for psychosis or schizophrenia.
When it came to anxiety and depression, the results were mixed. In non-medical studies, over half linked high-THC cannabis to worse anxiety, and 41% linked it to more depression. But among the studies looking at medical use, nearly half suggested that cannabis might help with anxiety and depression. Still, about a quarter of those studies found the opposite.
The review confirms what many doctors have already suspected—using stronger cannabis comes with higher mental health risks. However, the researchers also point out that the current evidence is not strong enough to give people clear advice. Many of the studies had design problems or lacked long-term follow-up.
The scientists call for more well-designed studies to better understand how high-THC cannabis affects mental health. Until then, they urge caution—especially for people who are at risk for mental illness.
If you care about mental health, please read studies about Middle-aged women with no kids may have this mental issue and findings of scientists find a cause of mental illnesses induced by childhood abuse.
For more about mental health, please read studies about Frequent painkiller use linked to mental health risks in these people and findings of Common depression drugs may offer new treatment for bipolar disorder.
The study is published in Annals of Internal Medicine.
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