A systematic review of 12 studies found 10 supporting a causal link between cannabis and schizophrenia, 8 showing symptom worsening, and 6 supporting therapeutic effects of CBD.
Psychiatrists, psychosis researchers, and cannabis policy makers interested in THC-CBD distinctions.
10 of 12 studies supported causal link; 6 supported CBD therapeutic effects
What the researchers found
After screening 96 articles and including 12 final studies (5 traditional reviews, 2 systematic reviews, 2 meta-analyses, 3 observational), 10 studies supported a causative link between cannabis and schizophrenia, 8 supported symptom exacerbation, and 6 supported therapeutic effects of CBD. The evidence points to THC as the primary risk component while CBD may counteract psychotic symptoms.
Why it matters
The opposing effects of THC and CBD on psychosis may explain why cannabis research has yielded contradictory findings. Separating these components could transform both risk assessment and treatment.
The numbers in context
96 initial results; 12 final studies included; 10 supported causative link; 8 supported exacerbation; 6 supported CBD therapeutic effects.
How the study worked
Systematic review of PubMed, PubMed Central, Cochrane Library, and Google Scholar for studies on cannabis and schizophrenia/psychosis published in the last 5 years. Quality assessment reduced 24 studies to 12 final inclusions.
What this study cannot tell us
Half the initial studies excluded for low quality; included studies were mostly reviews themselves (limited original data); small total evidence base (12 studies); did not quantify effect sizes.
How to read the evidence
Moderate: systematic methodology but many included studies were themselves reviews, and half of screened studies were excluded for low quality.
When this study was published
Published 2020.
The bigger picture
The consistent finding that THC increases psychosis risk while CBD may reduce it has direct implications for cannabis product regulation. High-THC/low-CBD products, increasingly common in legal markets, may carry the greatest risk.
Questions still open
- Would high-CBD/low-THC cannabis products carry less psychosis risk? Could CBD be developed as an adjunct treatment for schizophrenia?
Common questions
Does cannabis cause schizophrenia?
Can CBD help treat psychosis?
Read the original research
The Association Between Cannabis Use and Schizophrenia: Causative or Curative? A Systematic Review.
Cureus, 12(7), e9309
Citation
Patel, Shweta; Khan, Sahar; M, Saipavankumar; Hamid, Pousettef. (2020). The Association Between Cannabis Use and Schizophrenia: Causative or Curative? A Systematic Review.. Cureus, 12(7), e9309. https://doi.org/10.7759/cureus.9309
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