A review of 66 studies concluded cannabis doubles the risk of psychosis in vulnerable people, with dose and age effects
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.
Quick Facts
What This Study 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.
Key Numbers
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 They Did This
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.
Why This Research 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 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.
What This Study Doesn't 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.
Questions This Raises
- ?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?
Trust & Context
- Key Stat:
- Cannabis use doubles psychosis risk in vulnerable people
- Evidence Grade:
- Strong. Large review of 66 papers including 23 longitudinal cohort studies, representing decades of accumulated evidence.
- Study Age:
- Published in 2018 with literature through May 2018. The cannabis-psychosis association continues to be one of the most studied areas in cannabis research.
- Original Title:
- Cannabis consumption and psychosis or schizophrenia development.
- Published In:
- The International journal of social psychiatry, 64(7), 690-704 (2018)
- Authors:
- Ortiz-Medina, María Bettina, Perea, Marta, Torales, Julio(3), Ventriglio, Antonio, Vitrani, Giovanna, Aguilar, Lourdes, Roncero, Carlos
- Database ID:
- RTHC-01781
Evidence Hierarchy
Analyzes all available research on a topic using a structured method.
What do these levels mean? →Frequently Asked Questions
Does cannabis cause psychosis?
The evidence supports that cannabis approximately doubles the risk of psychosis in vulnerable individuals, with stronger effects at higher doses and earlier ages of use. However, most cannabis users do not develop psychosis, and genetic vulnerability plays a significant role in determining who is affected.
Who is "vulnerable" to cannabis-induced psychosis?
Vulnerability factors include family history of psychotic disorders, certain genetic variants (particularly in the COMT and AKT1 genes), earlier age of first cannabis use, heavy or daily use patterns, and use of high-potency cannabis.
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Cite This Study
https://rethinkthc.com/research/RTHC-01781APA
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
MLA
Ortiz-Medina, María Bettina, et al. "Cannabis consumption and psychosis or schizophrenia development.." The International journal of social psychiatry, 2018. https://doi.org/10.1177/0020764018801690
RethinkTHC
RethinkTHC Research Database. "Cannabis consumption and psychosis or schizophrenia developm..." RTHC-01781. Retrieved from https://rethinkthc.com/research/ortiz-medina-2018-cannabis-consumption-and-psychosis
Access the Original Study
Study data sourced from PubMed, a service of the U.S. National Library of Medicine, National Institutes of Health.
This study breakdown was produced by the RethinkTHC research team. We analyze and report published research findings without making health recommendations. All interpretations are based solely on the published abstract and study data.