UP-TO-DATE RESEARCH – Violent behavior and early onset of cannabis use in psychosis

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Situation to date:

The relation between substance abuse and violence in patients with mental disorders has been a topic of great interest, especially considering early phases of psychosis. Several studies have highlighted the risk of violent behavior in young people with psychosis, with substance use as a major risk factor for violence. Nonetheless, research exploring the links between cannabis use and violent behaviors in psychosis is still scarce and results are controversial. Little is known about the potential role of the age of onset of cannabis use on future violent behaviors.


A meta-analysis of articles published up to July 2019 was recently published in the American Journal of Psychiatry and investigated the extent to which cannabis use among youths is associated with the risk of perpetrating physical violence.  The study included 30 study arms, involving 296,815 adolescents and young adults <30 years. The pooled odds ratio (OR) for physical violence among cannabis users as compared with non-users was 2.11 (95% CI=1.64, 2.72). Preliminary evidence suggested that the risk of violence was higher for persistent heavy users compared with past-year users and lifetime users.

The moderate association between cannabis use and physical violence, regardless of study design and adjusting for confounding factors (i.e., socioeconomic factors, other substance use), encouraged the development of a study published in July 2020 by Valerie Moulin and colleagues. This study explored the impact of the age of onset of cannabis use on the risk of violent behaviors in a cohort of 265 early psychosis young people aged 18 to 35 years. Collecting data prospectively over a 36-month period, the researchers observed that 72 (27%) young people reported violent behaviors and 193 did not. While on average violent patients began using cannabis at age 15.29 years, non-violent patients started on average at age 16.97 years (p=0.004). Early-onset cannabis use (up to age 15) appeared as a potential risk factor for future violent behaviors (OR = 4.47; CI: 1.13–20.06), though the model was not sufficiently powered. Preliminary findings suggest that a history of violence and early cannabis use (until 15 years of age) might represent two key risk factors for violent behaviors in psychosis.


Take-home message:

Early-onset cannabis use may play a role in the emergence of violent behaviors in early phases of psychosis. Age at onset of cannabis use might inform clinicians regarding the need to propose more tailored interventions in order to prevent the perpetration of violence in this special population.

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Full reference:

Dellazizzo L, Potvin S, Dou BY, et al. Association Between the Use of Cannabis and Physical Violence in Youths: A Meta-Analytical Investigation. Am J Psychiatry. 2020;177(7):619-626. doi:10.1176/appi.ajp.2020.19101008

Moulin V, Alameda L, Framorando D, et al. Early onset of cannabis use and violent behavior in psychosis [published online ahead of print by Cambridge University Press, 2020 Jul 16]. Eur Psychiatry 2020; 1–17. doi: 10.1192/j.eurpsy.2020.71.

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