A systematic review of 66 papers (23 cohort studies, 43 reviews) concluded that cannabis use doubles the risk of developing psychosis in vulnerable people, with additional dose-response and age-of-first-use relationships, and gene-environment interactions that modulate the association.
Psychiatrists assessing cannabis-related psychosis risk; public health policymakers; young adults and their families making decisions about cannabis use.
Cannabis use doubles psychosis risk in vulnerable people
What the researchers found
Researchers reviewed 66 papers examining the relationship between cannabis use and psychosis in people without pre-existing schizophrenia.
The main conclusion: cannabis use doubles the risk of developing psychosis in vulnerable individuals.
Additional findings:
- A dose-response relationship exists: heavier cannabis use is associated with greater psychosis risk.
- Age of first use matters: earlier initiation is associated with higher risk.
- Gene-environment interactions modulate the association, meaning genetic susceptibility influences how much cannabis increases individual psychosis risk.
The evidence was drawn from 23 cohort studies (which follow people over time) and 43 reviews, representing a substantial evidence base accumulated over decades of research.
Why it matters
The doubling of psychosis risk is one of the most consistently replicated findings in cannabis research. This review synthesizes decades of evidence and adds clarity about dose, age, and genetic factors that modify the risk, helping to identify who is most vulnerable.
The numbers in context
66 papers reviewed (23 cohort, 43 reviews). Cannabis doubles psychosis risk in vulnerable people. Dose-response relationship documented. Age-of-first-use effect documented. Gene-environment interactions described.
How the study worked
Systematic review of PubMed database through May 2018. Keywords "cannabis" and "psychosis." 66 papers analyzed: 23 cohort studies, 43 reviews. Published in English and Spanish.
What this study cannot tell us
Narrative rather than quantitative meta-analysis. "Vulnerable people" is broadly defined. Most underlying studies cannot fully separate correlation from causation. Publication bias may inflate the association.
How to read the evidence
Strong. Large review of 66 papers including 23 longitudinal cohort studies, representing decades of accumulated evidence.
When this study was published
Published in 2018 with literature through May 2018. The cannabis-psychosis association continues to be one of the most studied areas in cannabis research.
The bigger picture
As cannabis becomes more accessible and potency increases, the population-level impact on psychosis incidence is a significant public health concern. This review reinforces that the risk is real but not uniform, opening the door for targeted prevention.
Questions still open
- Can genetic testing identify individuals at highest risk? Would switching to lower-potency or CBD-rich cannabis reduce psychosis risk? What interventions are most effective for high-risk cannabis users?
Common questions
Does cannabis cause psychosis?
Who is "vulnerable" to cannabis-induced psychosis?
Read the original research
Cannabis consumption and psychosis or schizophrenia development.
The International journal of social psychiatry, 64(7), 690-704
Citation
Ortiz-Medina, María Bettina; Perea, Marta; Torales, Julio; Ventriglio, Antonio; Vitrani, Giovanna; Aguilar, Lourdes; Roncero, Carlos. (2018). Cannabis consumption and psychosis or schizophrenia development.. The International journal of social psychiatry, 64(7), 690-704. https://doi.org/10.1177/0020764018801690
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