Cannabis and Psychosis: Five Key Insights

1. Cannabis potency is increasing — The concentration of tetrahydrocannabinol (THC) has increased fivefold in the last 20 years in Canada from about 4% to 20% in most legal dried cannabis.
2. High-potency and regular cannabis use is linked to increased risk of psychosis — The risk of psychosis is increased in people using high-potency THC (more than 10% THC), people using it frequently, and those who are younger and male. A history of mental disorders (depression, anxiety, etc.) also appears to increase the risk.
3. Cannabis-induced psychosis and cannabis use disorder increase the risk of schizophrenia — A recent study of 9.8 million people in Ontario found a 14.3-fold higher risk of developing a schizophrenia-spectrum disorder in people visiting the emergency department for cannabis use and a 241.6-fold higher risk from visits for cannabis-induced psychosis.
4. Treatment requires stopping cannabis and taking medication — Continued use of cannabis after a first episode of cannabis-induced psychosis is linked to greater risk of returning symptoms. Antipsychotic medication can help people with severe and prolonged symptoms.
5. Behavioural options may help with cannabis cessation — Motivational interviewing or cognitive behavioural therapy by a physician or psychologist can help build skills to resist cravings and follow treatment recommendations.

"Cannabis from the 2000s is not the same as in 2025," said coauthor Dr. Nicholas Fabiano, MD, resident and researcher with the Department of Psychiatry, University of Ottawa, Ottawa, Ontario. "THC content has increased by 5 times. This is likely a significant driver in the increasing link between cannabis use and schizophrenia."

"Cannabis and psychosis" is published August 11, 2025.