Daily cannabis use linked to 60% higher odds of violence in people with psychotic disorders
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.
Quick Facts
What This Study 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.
Key Numbers
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 They Did This
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.
Why This Research 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 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.
What This Study Doesn't 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.
Questions This Raises
- ?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?
Trust & Context
- Key Stat:
- Daily cannabis: 1.6x violence risk; daily stimulants: 2.8x risk
- Evidence Grade:
- Strong: two large nationwide samples with standardized assessments combined in meta-analysis.
- Study Age:
- Published 2020.
- Original Title:
- Use of illicit substances and violent behaviour in psychotic disorders: two nationwide case-control studies and meta-analyses.
- Published In:
- Psychological medicine, 50(12), 2028-2033 (2020)
- Authors:
- Lamsma, Jelle, Cahn, Wiepke, Fazel, Seena(2)
- Database ID:
- RTHC-02668
Evidence Hierarchy
Combines results from multiple studies to find an overall pattern.
What do these levels mean? →Frequently Asked Questions
Does cannabis cause violence in people with psychosis?
The study found an association between daily cannabis use and increased violence odds (1.6x), but the cross-sectional design cannot prove causation. Common underlying factors may contribute to both.
Was cannabis the most dangerous substance for violence risk?
No. Daily stimulant use (2.8x) and depressant use (2.2x) were associated with higher violence odds than daily cannabis use (1.6x) in people with psychotic disorders.
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Cite This Study
https://rethinkthc.com/research/RTHC-02668APA
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
MLA
Lamsma, Jelle, et al. "Use of illicit substances and violent behaviour in psychotic disorders: two nationwide case-control studies and meta-analyses.." Psychological medicine, 2020. https://doi.org/10.1017/S0033291719002125
RethinkTHC
RethinkTHC Research Database. "Use of illicit substances and violent behaviour in psychotic..." RTHC-02668. Retrieved from https://rethinkthc.com/research/lamsma-2020-use-of-illicit-substances
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.