Risk factors for violent behaviour in psychotic disorders: substance use and cognition
Keywords: psychosis
social cognition
substance use dependence
violence
schizophrenia
mentalizing
substance abuse
substance use disorder
aggression
theory of mind
executive function

Background People with psychotic disorders are at increased risk of violent behaviour. One of the most robust risk factors is problematic substance use. However, the effects of pharmacologically different categories of illicit substances (e.g. stimulants, hallucinogens) and nonproblematic use on violence risk remain unclear. Impairments in executive functions and mentalizing abilities – a key feature of psychotic disorders – are hypothesized to underly violent behaviour. However, the few studies investigating this hypothesis have produced conflicting results and used composite measures of executive functions. Additionally, previous studies have been limited by reliance on selective samples of male inpatients or prisoners and criminal records for the measurement of violence.
Methods Data came from Genetic Risk and Outcome of Psychosis, a multi-centre project in the Netherlands. Patients with psychotic disorders (N = 891) were recruited at various care settings (e.g. psychiatric hospitals, outpatient clinics) in geographically representative areas of the country. Problematic and nonproblematic use of alcohol, cannabis, stimulants, depressants and hallucinogens at any point in life were ascertained using the Composite International Diagnostic Interview-Substance Abuse Module. Neuropsychological tests were used to measure inhibition (Continuous Performance Test-HQ), cognitive flexibility (Response Shifting Task), fluid intelligence (Wechsler Adult Intelligence Scale-Third Edition [WAIS-III] Block Design subtest), planning (Neuropsychological Assessment Battery Mazes Test) and cognitive (Hinting Task) and affective (Degraded Facial Affect Recognition Task) mentalization. Lifetime violent behaviour was recorded with the Life Chart Schedule based on patient and parent interviews and case notes. In two studies, I investigated the associations of violence with: (i) problematic and nonproblematic use of each substance category using logistic regression; and (ii) performance on each neuropsychological test using analysis of covariance. All analyses were adjusted for age and gender.
Results Problematic and nonproblematic use increased the odds of violent behaviour between 20% and 100% across substance categories. The increases were significant for problematic use of alcohol (adjusted odds ratio [aOR] 1.7, 95% confidence interval [CI] [1.0, 1.3]), stimulants (aOR 2.0, 95% CI [1.3, 3.0]) and depressants (aOR 2.0, 95% CI [1.0, 3.9]), and nonproblematic use of hallucinogens (aOR 2.0, 95% CI [1.3, 3.1]). Violence accounted for 1% or less of the variance in performance across neuropsychological tests. Violent patients performed significantly worse than non-violent patients on the WAIS-III Block Design subtest (F [1, 847] = 5.1, p = .024) and Hinting Task (F [1, 839] = 9.4, p = .002).
Conclusions Problematic and nonproblematic use of all substance categories increase violence risk, which needs consideration in risk assessment and prevention. The small effect sizes suggest that deficits in fluid intelligence and cognitive mentalizing ability mainly have theoretical relevance. Future studies may improve our understanding of causal mechanisms with prospective designs and tests of additional possible confounders (e.g. genetics, childhood maltreatment) and mediators (e.g. treatment nonadherence, unemployment).