UP-TO-DATE RESEARCH Effects of illicit substance use on violent behaviour in patients with mental disorder

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The correlation between substance abuse and violence in patients with mental disorder is notorious. Previous evidence shows that a relationship between substance abuse and violent behaviour risk in psychotic patients might exist in many different ways:

  • psychopharmacological effects of intoxication with or withdrawal from substances;
  • induction or exacerbation of positive symptoms, which are risk factors for violent behaviour;
  • reduction of the therapeutic effects of antipsychotics;
  • avoidance or discontinuation of treatment;
  • perpetration of violence during the commission of crimes to gain access to substances or the money to buy them;
  • involvement in illegal drug markets where violent behaviour is common.

However, it was unclear how different categories of illicit substances and frequency of intake were associated with the risk of violent behaviour.

Situation to date:

  • studies about cannabis and stimulants use were few and produced conflicting results;
  • there have been no studies on depressants (besides alcohol) or hallucinogens;
  • it was uncertain whether subthreshold use – as opposed to Substance Use Disorder (SUD) – was a risk factor for violence.

The study:

A recent article, published in Aug. 2019 in Psychological Medicine (2018 Impact Factor: 5.641), investigates the associations of daily and nondaily intake with violent behaviour for cannabis, stimulants, depressants, and hallucinogens. It is described by its authors as “the largest study to investigate the relationship between use of illicit substances and violent behaviour in psychotic disorders”.

This work examines baseline data from two nationwide research projects:

  • Genetic Risk and Outcome of Psychosis (GROUP) (Korver et al., 2012) in the Netherlands and
  • National Evaluation of the Development and Impact of Early Intervention Services (NEDEN) (Birchwood et al., 2014) in England,

totaling 1792 individuals (73% male) with psychotic disorders drawn from diverse geographic areas and care settings. The mean age for the GROUP and the NEDEN study was about 27 and 23 years, respectively.

Findings show that, overall, daily and nondaily use of cannabis, stimulants, depressants, and hallucinogens were associated with violence behaviour. This was significant for:

  • daily use of cannabis, stimulants, depressants and (analyzed only in the NEDEN sample) hallucinogens as compared with nondaily use or no use;
  • nondaily use of stimulants and hallucinogens as compared with no use.

Hence, the authors believe that “strategies to prevent violent behaviour in psychotic disorders should target any substance use” and also that interventions, which currently focus on SUD, may assist in the prevention of violent behaviour in patients with subthreshold use.

The authors suggest that further studies using prospective designs and testing for additional confounders and mediators should endeavor to clarify the situation even more, especially about the psychopharmacological effects of substances and the causal mechanisms of violence in patients with mental disorder who use illicit substances.

The article full text is available at:


Full reference:

Lamsma J, Cahn W, Fazel S, GROUP and NEDEN investigators (2019). Use of illicit substances and violent behaviour in psychotic disorders: two nationwide case-control studies and meta-analyses. Psychological Medicine 1–6. doi: 10.1017/S0033291719002125

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