Cannabis use did not predict who developed psychosis among those already at clinical high risk
In a 2-year prospective study of 334 individuals at clinical high risk of psychosis, cannabis use at baseline was not significantly associated with transition to psychosis, symptom persistence, or functional outcome.
Quick Facts
What This Study Found
Among 334 clinical high-risk individuals followed for 2 years, 16.2% developed psychosis. There was no significant association between any measure of cannabis use at baseline (current use, previous use, frequency, age of onset) and transition to psychosis, persistence of symptoms, or functional outcome. Of those who did not develop psychosis, 51.4% had persistent symptoms and 48.6% were in remission.
Key Numbers
334 clinical high risk participants; 67 healthy controls; 16.2% transitioned to psychosis; 51.4% of non-transitioners had persistent symptoms; 48.6% in remission; 2-year follow-up
How They Did This
Prospective cohort study of 334 individuals at clinical high risk of psychosis and 67 healthy controls assessed at baseline using a modified Cannabis Experience Questionnaire, with 2-year follow-up. Transition assessed using CAARMS criteria; functioning assessed with GAF disability scale.
Why This Research Matters
This finding contrasts with epidemiological data suggesting cannabis increases psychosis risk. Among those already identified as high-risk, cannabis may not add predictive value beyond existing clinical indicators.
The Bigger Picture
If cannabis does not predict psychosis transition among those already at clinical high risk, the cannabis-psychosis association observed in population studies may reflect shared vulnerability rather than direct causation.
What This Study Doesn't Tell Us
Baseline-only cannabis assessment may miss changes in use during follow-up. Clinical high-risk sample may not generalize to general population. Relatively small sample for subgroup analyses. Cannabis use was self-reported.
Questions This Raises
- ?Does cannabis use during the high-risk period (not just at baseline) predict transition?
- ?Is the population-level cannabis-psychosis association driven entirely by shared risk factors?
Trust & Context
- Key Stat:
- No significant association between cannabis use and psychosis transition in high-risk individuals
- Evidence Grade:
- Multi-site prospective study with standardized assessments, but baseline-only cannabis measurement and relatively small transition subsample limit power.
- Study Age:
- Published 2023
- Original Title:
- Influence of cannabis use on incidence of psychosis in people at clinical high risk.
- Published In:
- Psychiatry and clinical neurosciences, 77(9), 469-477 (2023)
- Authors:
- Chester, Lucy A(2), Valmaggia, Lucia R, Kempton, Matthew J, Chesney, Edward, Oliver, Dominic, Hedges, Emily P, Klatsa, Elise, Stahl, Daniel, van der Gaag, Mark, de Haan, Lieuwe, Nelson, Barnaby, McGorry, Patrick, Amminger, G Paul, Riecher-Rössler, Anita, Studerus, Erich, Bressan, Rodrigo, Barrantes-Vidal, Neus, Krebs, Marie-Odile, Glenthøj, Birte, Nordentoft, Merete, Ruhrmann, Stephan, Sachs, Gabriele, McGuire, Philip
- Database ID:
- RTHC-04461
Evidence Hierarchy
Enrolls participants and follows them forward in time.
What do these levels mean? →Frequently Asked Questions
Does cannabis use predict psychosis in high-risk individuals?
In this 2-year prospective study of 334 people at clinical high risk, no measure of cannabis use at baseline predicted who would develop psychosis, who would have persistent symptoms, or who would have poor functioning.
How does this contrast with other cannabis-psychosis research?
Population-level studies consistently link cannabis use with psychosis risk, but this study found no such link among those already identified as high-risk, suggesting the association may reflect shared vulnerability rather than direct causation.
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Cite This Study
https://rethinkthc.com/research/RTHC-04461APA
Chester, Lucy A; Valmaggia, Lucia R; Kempton, Matthew J; Chesney, Edward; Oliver, Dominic; Hedges, Emily P; Klatsa, Elise; Stahl, Daniel; van der Gaag, Mark; de Haan, Lieuwe; Nelson, Barnaby; McGorry, Patrick; Amminger, G Paul; Riecher-Rössler, Anita; Studerus, Erich; Bressan, Rodrigo; Barrantes-Vidal, Neus; Krebs, Marie-Odile; Glenthøj, Birte; Nordentoft, Merete; Ruhrmann, Stephan; Sachs, Gabriele; McGuire, Philip. (2023). Influence of cannabis use on incidence of psychosis in people at clinical high risk.. Psychiatry and clinical neurosciences, 77(9), 469-477. https://doi.org/10.1111/pcn.13555
MLA
Chester, Lucy A, et al. "Influence of cannabis use on incidence of psychosis in people at clinical high risk.." Psychiatry and clinical neurosciences, 2023. https://doi.org/10.1111/pcn.13555
RethinkTHC
RethinkTHC Research Database. "Influence of cannabis use on incidence of psychosis in peopl..." RTHC-04461. Retrieved from https://rethinkthc.com/research/chester-2023-influence-of-cannabis-use
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.