A new study from Sweden's Karolinska Institutet suggests that bipolar disorder - or manic-depressive disorder - does not increase the risk of committing violent crime. Instead, the over-representation of individuals with bipolar disorder in violent crime statistics is almost entirely attributable to concurrent substance abuse.

The public debate on violent crime usually assumes that violence in the mentally ill is a direct result of the perpetrator's illness. Previous research has also suggested that patients with bipolar disorder - also known as manic-depressive disorder - are more likely to behave violently. However, it has 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.

The new study, carried out by researchers at Karolinska Institutet and Oxford University, is presented in the scientific journal Archives of General Psychiatry. 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.

21% of patients with bipolar disorder and a concurrent 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, and 3% among general public control individuals. The differences remained when accounting for age, gender, immigrant background, socio-economic status, and whether the most recent presentation of the bipolar disorder was manic or depressed.

"Interestingly, this concurs with our group's previous findings in schizophrenia, another serious psychiatric disorder, which found that individuals with schizophrenia are not more violent than members of the general public, provided there is no substance abuse," says professor Niklas Långström, head of the Centre for Violence Prevention at Karolinska Institutet, and one of the researchers behind the study.

According to the researchers, the findings support the need for initiatives to prevent, identify and treat substance abuse when fighting violent crime. Additionally, Långström hopes that the results will help challenge overly simplistic explanations of the causes of violent crime.

"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", Långström comments.