A major new study published this December in Psychological Medicine has found that regular cannabis use, especially of high-potency varieties, significantly increases the risk of developing psychotic disorders – regardless of a person’s genetic predisposition to schizophrenia.
The research, which examined data from two large studies involving over 145,000 people, discovered that daily cannabis users were nearly four times more likely to develop psychosis compared to non-users. For those using high-potency cannabis (containing 10% or more THC), the risk increased to five times higher.
Why This Matters
Importantly, these increased risks held true regardless of whether people had genetic risk factors for schizophrenia. This means even people with no family history or genetic predisposition to psychosis face significantly higher risks when regularly using cannabis, especially stronger varieties.
Key Findings:
- Daily cannabis use increased psychosis risk by 3.7 times
- High-potency cannabis daily use increased risk by 5.1 times
- These risks were independent of genetic factors
- Genetic risk for schizophrenia did not predict who would become a heavy cannabis user
- The combination of genetic risk and cannabis use did not multiply the risk beyond their separate effects
The study’s findings are particularly relevant given the increasing availability of high-potency cannabis worldwide and ongoing cannabis legalisation efforts. The researchers note that the 10% THC threshold they used to define “high-potency” is actually quite conservative by today’s standards, suggesting the risks could be even higher with modern cannabis products that often contain much more THC.
Challenging Previous Assumptions
This research challenges the idea that only people with a genetic predisposition need to worry about cannabis-related psychosis risk. The study’s authors emphasise that cannabis use represents an important and modifiable risk factor for psychosis that affects users regardless of their genetic makeup.
The researchers used genetic data from participants to calculate “polygenic risk scores” – essentially a measure of someone’s genetic predisposition to schizophrenia. They found that while these genetic factors did contribute to psychosis risk, they did not interact with or amplify the risks from cannabis use. The two risk factors appeared to operate independently.
Study Implications:
- Public health education about cannabis risks should target all users, not just those with family history of mental illness
- The increasing availability of high-potency cannabis may lead to higher rates of psychotic disorders
- Prevention efforts should focus on cannabis use as a modifiable risk factor
- The findings support considering potency limits in areas with legal cannabis
The research team emphasised that their findings provide important evidence for public education campaigns aimed at preventing increases in psychotic disorders as cannabis becomes more widely available and potent.
Research Strengths
This study represents one of the largest and most comprehensive investigations to date of how genetic risk factors and cannabis use interact to influence psychosis risk. It combined detailed data on cannabis use patterns with genetic information and clinical outcomes, providing robust evidence that cannabis use independently increases psychosis risk across all genetic profiles.
The authors note that while their study doesn’t definitively prove causation, it adds to a growing body of evidence suggesting cannabis is an important and modifiable risk factor for psychosis. They argue these findings should inform both public health messaging and policy discussions around cannabis regulation.
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