Cannabis Use Identified as a Novel Risk Factor for Violence in Psychosis With Odds Ratio of 3.34 | Research

The takeaway

A systematic review of 47 longitudinal studies (203,297 individuals) identified cannabis use as a novel risk factor for violence in people with psychosis (OR=3.34), alongside established factors like criminal history (OR=3.50) and substance misuse (OR=2.36).

Psychiatrists, forensic mental health professionals, violence risk assessors, and policymakers.

Cannabis use OR=3.34 for violence in psychosis

What the researchers found

Criminal history factors had the greatest risk (pooled OR 3.50, 95% CI: 2.37-5.16), followed by substance misuse (OR 2.36, 95% CI: 1.99-2.80). Cannabis use was identified as a novel risk factor in secondary analysis (OR 3.34, 95% CI: 2.32-4.82). Treatment-related factors were protective (OR 0.54, 95% CI: 0.34-0.85). Effects were attenuated in inpatient settings.

Why it matters

Violence risk assessment in psychosis is critical for clinical management. Cannabis use emerged as a novel and substantial risk factor with an odds ratio comparable to criminal history, suggesting it deserves routine assessment in violence risk evaluation.

The numbers in context

47 studies; 203,297 individuals; cannabis OR=3.34 (95% CI: 2.32-4.82); criminal history OR=3.50; substance misuse OR=2.36; treatment protective OR=0.54.

How the study worked

Systematic review and meta-analysis searching five databases through June 2022. 47 longitudinal studies, 41 independent samples, 203,297 individuals. Random-effects meta-analysis for risk factors reported in 3+ independent samples. 10-year update of a prior review.

What this study cannot tell us

Cannabis finding from secondary analysis needs replication. Most studies from high-income countries. Heterogeneity in violence definitions. Cannot establish causation from observational data.

How to read the evidence

Large-scale systematic review of longitudinal studies with meta-analysis provides strong evidence, though cannabis finding requires replication.

When this study was published

2025 10-year update published in the British Journal of Psychiatry.

The bigger picture

The identification of cannabis as a risk factor for violence in psychosis adds clinical urgency to addressing cannabis use in this population. Combined with the protective effect of treatment, it suggests that engaging psychosis patients in treatment and addressing cannabis use could reduce violence risk.

Questions still open

Does reducing cannabis use in psychosis patients reduce violence risk?
Is the cannabis-violence association specific to certain types of psychosis?

Common questions

Does cannabis increase violence risk in people with psychosis?

This meta-analysis found cannabis use was associated with a 3.34x higher odds of violence in people with psychosis, making it comparable to criminal history as a risk factor.

What reduces violence risk in psychosis?

Treatment-related factors were protective (OR=0.54), suggesting that engaging patients in treatment is one of the strongest approaches to reducing violence risk.

Read the original research

Systematic review of risk factors for violence in psychosis: 10-year update.

The British journal of psychiatry : the journal of mental science, 226(2), 100-107

View on PubMed ↗Publisher’s paper ↗

Citation

Lagerberg, Tyra; Lambe, Sinéad; Paulino, Anabelle; Yu, Rongqin; Fazel, Seena. (2025). Systematic review of risk factors for violence in psychosis: 10-year update.. The British journal of psychiatry : the journal of mental science, 226(2), 100-107. https://doi.org/10.1192/bjp.2024.120