Cannabis today is not the cannabis of two decades ago. According to a new peer-reviewed review in the Canadian Medical Association Journal, the concentration of tetrahydrocannabinol (THC) in most legal dried cannabis has surged from about 4% in the early 2000s to more than 20% in 2023.
Researchers warn that high-potency and frequent cannabis use is linked to a greater risk of psychosis, particularly in younger men and those with pre-existing mental health conditions. The findings arrive as public perceptions of cannabis safety continue to evolve, raising questions about how much potency matters when it comes to brain health.
Potency Has Risen Dramatically
THC, the main psychoactive component of cannabis, has roughly quintupled in concentration over the past 20 years. The shift reflects market trends toward stronger products, but also changes in cultivation practices. This steep rise in potency could be a major factor driving the observed associations with psychosis, said coauthor Dr. Nicholas Fabiano of the University of Ottawa.
“Cannabis from the 2000s is not the same as in 2025. THC content has increased by 5 times. This is likely a significant driver in the increasing link between cannabis use and schizophrenia.”
Who Is Most at Risk?
Data suggest that people using products with more than 10% THC, using cannabis regularly, or starting young are at elevated risk. Men, and those with a history of bipolar disorder, depression, or anxiety, may be particularly vulnerable. While more than half of people with cannabis-associated psychosis recover within a day, prolonged symptoms often require hospitalization.
Cannabis-Induced Psychosis Can Lead to Schizophrenia
One large Ontario cohort study of 9.8 million people found stark differences in risk. Within three years of an emergency department visit, people with cannabis-induced psychosis were over 240 times more likely to develop a schizophrenia-spectrum disorder compared to the general population. Even those seen for cannabis use without psychosis had a 14-fold increase in risk.
Treatment Means Stopping Cannabis
The mainstay of care for cannabis-induced psychosis is complete abstinence from cannabis. Second-generation antipsychotics may be used for severe or persistent symptoms, with gradual tapering once the acute episode resolves. Continued cannabis use after a first episode greatly increases the likelihood of recurrence.
Behavioral Support Can Help People Quit
- Motivational interviewing can boost treatment engagement.
- Cognitive behavioural therapy builds coping strategies to resist cravings.
- Both approaches can reduce cannabis use, lessen psychiatric symptoms, and improve daily functioning.
Looking Ahead
With legalization making cannabis more accessible, and potency at historic highs, public health experts stress the importance of awareness campaigns, targeted interventions for at-risk groups, and clinical vigilance. As the CMAJ authors note, the cannabis landscape has shifted, and so must our approach to its mental health impacts.
Journal: Canadian Medical Association Journal
DOI: 10.1503/cmaj.250659
Publication Date: August 11, 2025
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