Substance abuse, schizophrenia and risk of violence

A study published this week in the open access journal PLoS Medicine demonstrates that there is an association between schizophrenia and violence, but shows that this association is greatly increased by drug and alcohol abuse. Importantly, the study also finds that the risk of violence from patients with psychoses who also have substance use disorder is no greater than those who have a substance use disorder but who do not have a psychotic illness – in other words, schizophrenia and other psychotic illnesses do not appear to be responsible for any additional risk of violence above the increased risk associated with substance abuse. Potentially this finding has implications for attempts to reduce violence in society, suggesting that strategies aimed at reducing drug and alcohol abuse would be more successful than focusing on mental illness.

Whether or not there is a link between psychotic illnesses and violence has been disputed in the medical literature as well as being a controversial issue with far-reaching social and policy implications. Seena Fazel, of the Department of Psychiatry at the University of Oxford, and colleagues conducted a systematic review of all previous studies examining psychotic illness and the risk of violence to try and resolve their varied conclusions – some of the previous studies concluded that there is no increased risk of violence from patients with schizophrenia, whilst others have reported that there is a marked increase in the risk of violence in individuals with schizophrenia.

The opinion emerging in the last couple of decades that there is a modest association between schizophrenia and violence is thought to have influenced policy and legal developments, with the number of patients in secure hospitals increasing in Western countries. Man y mental health charities and clinicians specializing in mental health contest this opinion – arguing that the perception that people with mental illness are more violent is a myth reinforced by the media, contributing to a social stigma around mental illness that damages many people and prevents understanding.

In their systematic review, the researchers identified 20 studies that compared the risk of violence among people with psychotic illness with those in the general population. Using statistical tools to allow for the differences between the studies, the researchers found that the risk of violent outcomes did increase for individuals with schizophrenia or other psychoses. Men with schizophrenia or other psychoses were typically four to five times as likely to commit a violent act as a man in the general population; for women with schizophrenia or other psychoses there was an eight times greater risk of violence than women in the general population – although the researchers suggest this might be explained by the lower prevalence of alcohol and drug use in the general female population. When analysing the characteristics that differed between the studies, including study location and whether the diagnosis was for schizophrenia or another psychotic disorder, the researchers found that substance abuse was the only factor causing variation between the studies. Substance abuse greatly increased the risk of violence for those with a psychotic illness, but this increased risk of violence was similar to those in the general population with substance abuse but no psychotic illness – suggesting that most of the excess risk of violence in psychotic patients appears to be mediated by the abuse of drugs and alcohol.