Use of illicit substances and violent behaviour in psychotic disorders: two nationwide case-control studies and meta-analyses

In people with psychotic disorders, daily use of cannabis, stimulants, and depressants significantly increases the odds of violent behavior, as does nondaily use of stimulants and hallucinogens. Daily cannabis use was associated with 1.6 times higher odds of violence, daily stimulant use with 2.8 times higher odds, and daily depressant use with 2.2 times higher odds. Nondaily stimulant use raised odds by 1.6 times, and nondaily hallucinogen use by 1.5 times. Daily hallucinogen use, analyzed only in the UK sample, increased odds 3.3-fold. The findings suggest that any substance use, not just daily use, should be targeted to prevent violence in this population.

Study at a glance

Abstract

Abstract Background Substance use disorder explains much of the excess risk of violent behaviour in psychotic disorders. However, it is unclear to what extent the pharmacological properties and subthreshold use of illicit substances are associated with violence. Methods Individuals with psychotic disorders were recruited for two nationwide projects: GROUP ( N = 871) in the Netherlands and NEDEN ( N = 921) in the United Kingdom. Substance use and violent behaviour were assessed with standardized instruments and multiple sources of information. First, we used logistic regression models to estimate the associations of daily and nondaily use with violence for cannabis, stimulants, depressants and hallucinogens in the GROUP and NEDEN samples separately. Adjustments were made for age, sex and educational level. We then combined the results in random-effects meta-analyses. Results Daily use, compared with nondaily or no use, and nondaily use, compared with no use, increased the pooled odds of violence in people with psychotic disorders for all substance categories. The increases were significant for daily use of cannabis [pooled odds ratio (pOR) 1.6, 95% confidence interval (CI) 1.2–2.0), stimulants (pOR 2.8, 95% CI 1.7–4.5) and depressants (pOR 2.2, 95% CI 1.1–4.5), and nondaily use of stimulants (pOR 1.6, 95% CI 1.2–2.0) and hallucinogens (pOR 1.5, 95% CI 1.1–2.1). Daily use of hallucinogens, which could only be analysed in the NEDEN sample, significantly increased the risk of violence (adjusted odds ratio 3.3, 95% CI 1.2–9.3). Conclusions Strategies to prevent violent behaviour in psychotic disorders should target any substance use.