A meta-analysis of 37 studies found cannabis use prevalence of 33.7% at first psychosis onset, with regular use typically beginning 6.3 years before psychosis, and use declining by nearly half after treatment.
Read this if you want to understand the timeline and prevalence of cannabis use in relation to psychotic disorders.
6.3 years between starting regular cannabis use and psychosis onset
What the researchers found
This meta-analysis pooled data from 37 studies to characterize the epidemiology of cannabis use in first-episode psychosis.
Three key findings emerged. First, the interval between starting regular cannabis use and psychosis onset averaged 6.3 years. This long delay is important for understanding the temporal relationship between cannabis and psychosis.
Second, approximately one-third (33.7%) of people experiencing first-episode psychosis were using cannabis at the time of onset. This is substantially higher than general population cannabis use rates.
Third, cannabis use declined after psychosis treatment, with odds of continued use between 6 months and 10 years after onset being 0.56 (meaning about 44% reduction). This suggests that treatment engagement and psychosis experience lead many to reduce or stop cannabis use.
Why it matters
This meta-analysis provides the most precise estimates to date of the cannabis-psychosis timeline. The 6.3-year average between regular cannabis use onset and psychosis emergence defines a potential intervention window during which reducing cannabis use might prevent or delay psychosis onset.
The numbers in context
37 samples included. Interval from regular cannabis to psychosis onset: 6.3 years (10 samples, SMD = 1.56). Cannabis use prevalence at first episode: 33.7% (35 samples, 95% CI 31-39%). Odds of continued use after treatment: 0.56 (19 samples, 95% CI 0.40-0.79).
How the study worked
Meta-analysis of 37 observational studies identified through MEDLINE, EMBASE, PsycINFO, Web of Science, and CINAHL. Random-effects meta-analyses synthesized prevalence estimates, intervals between cannabis initiation and psychosis onset, and odds of continued cannabis use after treatment.
What this study cannot tell us
Observational studies cannot prove causation. Heterogeneity across studies was noted. Recall bias in reporting cannabis use onset age. Different studies defined cannabis use differently. The meta-analysis cannot distinguish between causation and shared vulnerability.
How to read the evidence
Meta-analysis of 37 studies with random-effects methodology. Strong synthesis of observational evidence, though underlying studies have inherent limitations.
When this study was published
Published in 2016. Additional studies have continued to refine estimates of the cannabis-psychosis relationship.
The bigger picture
The 6.3-year window between cannabis initiation and psychosis onset is clinically actionable. It suggests that early intervention programs targeting cannabis use in high-risk individuals could have years of lead time before psychosis develops. The post-treatment decline in use also suggests that psychosis itself motivates many users to change their behavior.
Questions still open
- Would cannabis cessation during the 6.3-year window prevent psychosis in some individuals? Why do about 56% of cannabis users continue after psychosis despite evidence of harm? What predicts continued versus discontinued use?
Common questions
How common is cannabis use among people experiencing first-episode psychosis?
How long before psychosis do people typically start using cannabis?
Read the original research
Cannabis use in first episode psychosis: Meta-analysis of prevalence, and the time course of initiation and continued use.
The Australian and New Zealand journal of psychiatry, 50(3), 208-19
Citation
Myles, Hannah; Myles, Nicholas; Large, Matthew. (2016). Cannabis use in first episode psychosis: Meta-analysis of prevalence, and the time course of initiation and continued use.. The Australian and New Zealand journal of psychiatry, 50(3), 208-19. https://doi.org/10.1177/0004867415599846
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