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The link between psychosis and violence is not clear cut

Jeroen Ensink’s life was cut short when a man with mental health problems stabbed him to death outside his flat in north London. At an inquest, Ensink’s widow, demanded to know why mental health homicides “keep happening again and again”.

Murders committed by people suffering from schizophrenia or psychosis make headlines and it’s easy to see why some people are afraid of people with mental illness. However, the scientific evidence linking schizophrenia with violent crime is not clear. Some studies looking at the relationship between psychosis and violence suggest that there is a strong relationship while others provide weak or no evidence that people with schizophrenia are more violent.

Substance abuse

One of the big problems for research in this area is separating schizophrenia from the effects of the many other difficulties that people suffering from schizophrenia often have. Substance abuse is thought to be one of the factors that contributes to increased risk for violence in people with schizophrenia.

A meta-analysis of 20 studies, published in PLOS Medicine in 2009, examined the links between psychosis, substance misuse and violence. The results suggest that most of the increased risk for violence was due to substance abuse. The authors of this study conclude that policy designed to control violence should focus on substance misuse rather than psychosis.

Substance abuse complicates the stats. tommaso79/

The same study, however, also looked at the very small number of studies that had focused on homicide rather than less serious violence. The results showed that people suffering from psychosis – with or without comorbid substance abuse – were nearly 20 times more likely to kill another person than would be expected in the general population.

The evidence seems to support public fear of schizophrenics and it seems unsurprising that people should call for action from policymakers to reduce this risk by implementing stricter control of people who are suffering from mental illness. The problem is that homicide is very rare both in people with and without schizophrenia.

Many people with schizophrenia, who pose no threat to anyone, would have to be detained in order to prevent just one incident of serious violence. There is huge potential financial cost and also a social cost in terms of lost liberty for many innocent people. The problem of devising a foolproof method of deciding who to detain and who to leave at liberty may in fact never be resolved because of the complexity of the causes of individual episodes of violence.

What we should focus on

Finally, our attention is inevitably grabbed by high profile and tragic failures in the management of people with schizophrenia who kill. But our attention is never directed to the many thousands of people throughout the UK who suffer from schizophrenia but live happy and productive lives. Unfortunately, successful management of people with schizophrenia is never likely to be newsworthy but the absence of focus on positive and effective aspects of current support for mentally ill people may mean that we are missing some valuable lessons in how to avoid future tragedies.

Knowing what works is surely as important as trying to avoid what went wrong last time. But there has been very little attention paid to how effective our psychiatric services are in terms of reducing harm, or which specific aspects of patient management or treatment help people with schizophrenia to stay out of hospital and out of trouble. Too often in the past we have seen policy driven by knee-jerk reactions to tragedy, perhaps now is the time for policymakers and researchers to change focus and find out what works.

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