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

Jelle Lamsma,Seena Fazel,Wiepke Cahn

doi:10.1017/s0033291719002125

Jelle Lamsma, Seena Fazel + Show 1 more

Open Access

https://doi.org/10.1017/s0033291719002125

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Abstract

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. 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. 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). Strategies to prevent violent behaviour in psychotic disorders should target any substance use.

Highlights

Much of the excess risk of violent behaviour in psychotic disorders can be explained by substance use disorder (SUD) (Fazel et al, 2009)
The increases were significant for daily use of stimulants [adjusted odds ratio 2.2, 95% confidence interval (CI) 1.3–3.8] and nondaily use of hallucinogens
Pooled across the Genetic Risk and Outcome of Psychosis (GROUP) and NEDEN samples, daily use of cannabis, stimulants and depressants significantly increased the odds of violence compared with nondaily or no use

Summary

Introduction

Much of the excess risk of violent behaviour in psychotic disorders can be explained by substance use disorder (SUD) (Fazel et al, 2009). It is unclear to what extent different categories of illicit substances, as defined by their psychopharmacological effects, are related to violent behaviour Another uncertainty is whether subthreshold use, as opposed to SUD, is a risk factor for violence. The few studies of cannabis (Koen et al, 2004; Moulin et al, 2018; Oluwoye et al, 2019) and stimulants (Bell et al, 2002; Miles et al, 2003; Harris et al, 2010) have produced conflicting results These studies have been limited by small samples of inpatients and proxy measures of violent behaviour (e.g. hostility, aggression).

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