Two nationwide studies combined in a meta-analysis found that daily cannabis use significantly increased the odds of violent behavior in people with psychotic disorders.
Psychiatrists, forensic mental health professionals, and violence risk assessment researchers.
Daily cannabis: 1.6x violence risk; daily stimulants: 2.8x risk
What the researchers found
Across two large nationwide samples (GROUP, Netherlands, N=871; NEDEN, UK, N=921), daily cannabis use was associated with 1.6 times higher odds of violence in people with psychotic disorders (pooled OR 1.6, 95% CI 1.2-2.0). Daily stimulant use (pOR 2.8) and daily depressant use (pOR 2.2) carried even higher risks.
Why it matters
Violence risk in psychotic disorders is a major clinical and public health concern. Understanding the specific contribution of different substances helps target prevention strategies.
The numbers in context
1,792 total participants; daily cannabis: pOR 1.6 (1.2-2.0); daily stimulants: pOR 2.8 (1.7-4.5); daily depressants: pOR 2.2 (1.1-4.5); nondaily cannabis use did not significantly increase violence risk.
How the study worked
Two nationwide case-control studies (Netherlands and UK) with standardized substance use and violence assessments, combined in random-effects meta-analyses. Adjusted for age, sex, and education.
What this study cannot tell us
Cross-sectional assessment of substance use; cannabis use self-reported; cannot establish whether substance use causes violence or shares common risk factors; adjusted for limited confounders only.
How to read the evidence
Strong: two large nationwide samples with standardized assessments combined in meta-analysis.
When this study was published
Published 2020.
The bigger picture
While daily cannabis use increased violence odds in psychotic disorders, it was the least risky substance compared to stimulants and depressants. This nuanced picture challenges both minimization and exaggeration of cannabis-related risk in this population.
Questions still open
- Does reducing cannabis use frequency below daily levels meaningfully reduce violence risk? Are the effects driven by THC content, or would high-CBD strains show different patterns?
Common questions
Does cannabis cause violence in people with psychosis?
Was cannabis the most dangerous substance for violence risk?
Read the original research
Use of illicit substances and violent behaviour in psychotic disorders: two nationwide case-control studies and meta-analyses.
Psychological medicine, 50(12), 2028-2033
Citation
Lamsma, Jelle; Cahn, Wiepke; Fazel, Seena. (2020). Use of illicit substances and violent behaviour in psychotic disorders: two nationwide case-control studies and meta-analyses.. Psychological medicine, 50(12), 2028-2033. https://doi.org/10.1017/S0033291719002125
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