Umbrella review of 26 reviews confirms dose-dependent link between cannabis use and psychosis
A systematic review of 26 meta-analyses and systematic reviews confirmed that cannabis use is associated with increased psychosis risk in a dose-dependent manner, earlier psychosis onset, higher relapse rates, and more prominent positive symptoms.
Quick Facts
What This Study Found
Across 26 reviews, the evidence consistently showed: psychosis occurs more frequently in cannabis users than non-users; risk increases with dose; cannabis users develop psychosis earlier; and cannabis use is associated with increased relapse, more hospitalizations, and more pronounced positive symptoms in those with psychotic disorders.
Key Numbers
26 systematic reviews and meta-analyses included. Dose-dependent risk for psychotic illness. Earlier onset in cannabis users. Higher relapse rates and more hospitalizations in psychotic patients who use cannabis.
How They Did This
Systematic review of meta-analyses and systematic reviews from five databases (2005-2016). 26 publications were included and evaluated for methodological quality, which ranged from high to poor.
Why This Research Matters
As an umbrella review (review of reviews), this represents the highest level of evidence synthesis available, providing a comprehensive summary of the cannabis-psychosis relationship across the entire published literature.
The Bigger Picture
While the umbrella review confirms the association, the included reviews varied in quality (high to poor), and the fundamental question of whether cannabis causes psychosis or is associated through shared risk factors remains incompletely resolved.
What This Study Doesn't Tell Us
Methodological quality varied across included reviews. The umbrella review inherits the limitations of the underlying studies, which are predominantly observational. Publication bias may favor studies finding positive associations.
Questions This Raises
- ?Can the dose-response relationship be used to establish safe use thresholds?
- ?What proportion of the association is causal versus due to shared genetic vulnerability?
- ?Would reducing cannabis potency reduce psychosis risk at the population level?
Trust & Context
- Key Stat:
- 26 reviews confirm dose-dependent cannabis-psychosis association
- Evidence Grade:
- Strong: umbrella review synthesizing 26 meta-analyses and systematic reviews, the highest level of evidence synthesis.
- Study Age:
- Published in 2020 in European Archives of Psychiatry and Clinical Neuroscience.
- Original Title:
- Cannabis use and psychosis: a review of reviews.
- Published In:
- European archives of psychiatry and clinical neuroscience, 270(4), 403-412 (2020)
- Authors:
- Hasan, Alkomiet(3), von Keller, Rupert(2), Friemel, Chris Maria, Hall, Wayne, Schneider, Miriam, Koethe, Dagmar, Leweke, F Markus, Strube, Wolfgang, Hoch, Eva
- Database ID:
- RTHC-02602
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 consistently shows an association that is dose-dependent: the more cannabis a person uses, the higher their risk of psychotic illness. However, proving direct causation is difficult because observational studies cannot fully rule out shared genetic or environmental risk factors.
What about people who already have psychosis?
The review found that cannabis use in people with existing psychotic disorders is associated with higher relapse rates, more hospitalizations, and more prominent positive symptoms (like hallucinations and delusions).
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Cite This Study
https://rethinkthc.com/research/RTHC-02602APA
Hasan, Alkomiet; von Keller, Rupert; Friemel, Chris Maria; Hall, Wayne; Schneider, Miriam; Koethe, Dagmar; Leweke, F Markus; Strube, Wolfgang; Hoch, Eva. (2020). Cannabis use and psychosis: a review of reviews.. European archives of psychiatry and clinical neuroscience, 270(4), 403-412. https://doi.org/10.1007/s00406-019-01068-z
MLA
Hasan, Alkomiet, et al. "Cannabis use and psychosis: a review of reviews.." European archives of psychiatry and clinical neuroscience, 2020. https://doi.org/10.1007/s00406-019-01068-z
RethinkTHC
RethinkTHC Research Database. "Cannabis use and psychosis: a review of reviews." RTHC-02602. Retrieved from https://rethinkthc.com/research/hasan-2020-cannabis-use-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.