Drugs and alcohol, not mental illness, explains violent crime risk

Bipolar disorder by itself does not increase the risk of committing violent crime, suggests a new study by Oxford University and the Karolinska Institutet in Sweden. Instead, the over-representation of individuals with bipolar disorder in violent crime statistics is almost entirely attributable to concurrent drug or alcohol abuse.

This mirrors arecent studyin schizophrenia by the same group which showed a minimal association with violent crime, unless there is also a drug or alcohol problem.

‘In people without substance abuse problems, bipolar disorder is not a problem for violent crime,’ says Dr Seena Fazel of the Department of Psychiatry at Oxford University.

The public debate on violent crime usually assumes that violence in the mentally ill is a direct result of the perpetrator’s illness. However, it has previously been unclear if the violence is due to the bipolar disorder per se, or caused by other aspects of the individual’s personality or lifestyle. 

Dr Fazel explains that reviewing all the available evidence suggests that the risk of violent crime among anyone in the general population who abuses drugs or alcohol is 6–8 times greater than those who don’t.

The risk of violent crime among those with bipolar disorder who also have substance abuse problems is raised by the same amount: 6–7 times, suggesting that the mental illness has little or no role.

However, levels of diagnosed substance abuse among those with bipolar disorder and schizophrenia run at around 20–25%, and are greater than the 2% seen in the general population.

‘This shows we need to focus our attention on how we can detect those individuals with bipolar disorder and schizophrenia with substance abuse problems, and prevent and treat those who are abusing substances,’ says Dr Fazel.

In the new study published in the journal Archives of General Psychiatry, the researchers compared the rate of violent crime in over 3,700 patients with bipolar disorder cared for in Swedish hospitals between 1973 and 2004 with that of 37,000 control individuals from the general public.

Violent crime included murder, manslaughter, any form of assault, sex crimes, robbery, arson and illegal threats or intimidation.

21% of patients with bipolar disorder and a diagnosis of severe substance abuse (alcohol or illegal drugs) were convicted of violent crimes, compared to 5% of those with bipolar disorder but without substance abuse, 5% among the unaffected siblings of bipolar patients, and 3% among general public control individuals.

‘Interestingly, this concurs with our group’s previous findings in schizophrenia – another serious psychiatric disorder,’ says professor Niklas Långström, Head of the Centre for Violence Prevention at Karolinska Institutet, and one of the researchers behind the study. ‘Unwarranted fear and stigmatisation of mental illness increases the alienation of people with psychiatric disorder and makes them less inclined to seek the care they need.’

The researchers say that the findings support the need for initiatives to prevent, identify and treat drug and alcohol abuse when fighting violent crime.