Cannabis use did not predict who developed psychosis among those already at clinical high risk | Research

The takeaway

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.

Psychosis prevention researchers, clinical high-risk program clinicians, psychiatric epidemiologists

No significant association between cannabis use and psychosis transition in high-risk individuals

What the researchers 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.

Why it 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 numbers in context

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 the study worked

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.

What this study cannot 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.

How to read the evidence

Multi-site prospective study with standardized assessments, but baseline-only cannabis measurement and relatively small transition subsample limit power.

When this study was published

Published 2023

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.

Questions still open

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?

Common 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.

Read the original research

Influence of cannabis use on incidence of psychosis in people at clinical high risk.

Psychiatry and clinical neurosciences, 77(9), 469-477

View on PubMed ↗Publisher’s paper ↗

Citation

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