Small risk of violence in schizophrenia unless drugs and alcohol are involved

There is an association between schizophrenia and violent crime, but it is minimal unless there are also drug or alcohol problems, a large-scale study led by Oxford University has shown.

The findings, reported in the Journal of the American Medical Association, highlight the importance of treating drug or alcohol problems in people with severe mental illness.

‘We have found that the risk of violent crime committed by people with schizophrenia is a lot lower than people might expect,’ says Dr Seena Fazel of the Department of Psychiatry at Oxford University. ‘This will be of no consolation to victims of such crimes or their families, I know. But by also identifying the mediating role of drugs and alcohol, it should be possible to reduce the risk of violence in people with schizophrenia through evidence-based treatments for drug and alcohol abuse.’

The researchers compared the risk of violent crime in over 8,000 people with schizophrenia with over 80,000 controls from the general population, using over 30 years of data from Swedish records of hospital admissions and criminal convictions. This makes the study larger than all previous studies of this kind put together.

The team also collected data for the more than 8,000 unaffected brothers and sisters of the people with schizophrenia, as a further means of controlling for effects of social class, family environment and upbringing. 

The researchers from Oxford University, as well as the Karolinska Institutet, Stockholm University, and the University of Uppsala in Sweden, found that there was an association between schizophrenia and violent crime. People with schizophrenia were twice as likely to have committed a violent offence than controls in the general population: 12–13% of individuals with schizophrenia has been convicted of a violent crime compared with between 5% and 8% of individuals without schizophrenia.

When compared with their unaffected brothers and sisters, people with schizophrenia showed an increase in risk of violent crime of 1.6 times.

However, this increased risk of violent crime among people with schizophrenia is very different depending on whether they also have drug or alcohol problems. Risk of violent crime among those who have schizophrenia and abuse drug or alcohol is more than four fold greater than the general population. But among those who do not suffer from abuse of drugs and alcohol, it is increased only minimally. The risk is 1.2 times greater.‘

The message for mental health professionals is this: if you are seeing patients with schizophrenia who also have drug or alcohol problems, take it seriously,’ says Dr Fazel. ‘These problems are prevalent in schizophrenia, but there are evidence-based treatment strategies for drug and alcohol abuse and so the risk of violence can be reduced.’

‘It is clear that mental health services have the potential to help in the prevention of violence, particularly if patients with severe mental illness receive thorough assessment and appropriate treatment. We know that up to 5% of violent crimes in society are committed by people with schizophrenia.’

‘At the same time, there is no reason why many individuals, especially those who show no problems with drugs or alcohol, can’t be integrated into normal life,’ he adds.