Starting cannabis before age 15 quadrupled violence risk in early psychosis patients | Research

The takeaway

Among 265 early psychosis patients, those who started using cannabis before age 15 had 4.5 times the odds of violent behavior, even after adjusting for other risk factors.

Psychiatrists, forensic mental health professionals, early psychosis clinicians, and adolescent prevention programs.

Cannabis before age 15: 4.5x higher violence odds in psychosis (OR 4.47)

What the researchers found

In a 36-month prospective cohort of 265 early psychosis patients, violent patients began cannabis use at an average age of 15.3 vs. 17.0 for nonviolent patients (p=0.004). Early-onset cannabis use (before age 15) was an independent risk factor for violent behavior (OR 4.47, CI 1.13-20.06) after adjustment for age, other substance use, and known violence risk factors.

Why it matters

Violence in psychosis is a serious clinical and public health concern. Identifying early cannabis use as an independent risk factor suggests a modifiable target for prevention.

The numbers in context

265 patients; 72 violent, 193 nonviolent; violent started cannabis at 15.3 vs 17.0; early onset (≤15) OR 4.47 (1.13-20.06) for violence; 36-month follow-up.

How the study worked

Prospective cohort study following 265 early psychosis patients (ages 18-35) for 36 months, using logistic regression to assess link between age of cannabis onset and violent behavior, adjusting for multiple covariates.

What this study cannot tell us

Wide confidence interval (1.13-20.06) suggests imprecision; age of cannabis onset was self-reported; violence was broadly defined; cannot prove causation; relatively small sample for subgroup analysis.

How to read the evidence

Moderate: prospective design with appropriate adjustments, but wide confidence interval and self-reported exposure.

When this study was published

Published 2020.

The bigger picture

This adds to evidence that the timing of cannabis exposure matters as much as whether someone uses at all. The adolescent brain may be particularly vulnerable to cannabis effects that increase later aggression in the context of psychosis.

Questions still open

Would delaying cannabis initiation even by 1-2 years reduce violence risk in psychosis-prone youth? What mechanism connects early cannabis use to later violence?

Common questions

Does the age of first cannabis use matter for violence risk?

Yes. In this study, starting before age 15 was associated with 4.5 times higher odds of violent behavior in early psychosis patients, even after controlling for other risk factors.

Is cannabis use itself the risk factor, or just early use?

Being a cannabis user vs. non-user was controlled for in the analysis. It was specifically the early onset (before 15) that emerged as the independent risk factor for violence.

Read the original research

Early onset of cannabis use and violent behavior in psychosis.

European psychiatry : the journal of the Association of European Psychiatrists, 63(1), e78

View on PubMed ↗Publisher’s paper ↗

Citation

Moulin, Valerie; Alameda, Luis; Framorando, David; Baumann, Philipp-S; Gholam, Mehdi; Gasser, Jacques; Do Cuenod, Kim-Q; Conus, Philippe. (2020). Early onset of cannabis use and violent behavior in psychosis.. European psychiatry : the journal of the Association of European Psychiatrists, 63(1), e78. https://doi.org/10.1192/j.eurpsy.2020.71