Severe mental illness does not cause violent behaviour, except when drugs or alcohol are involved, suggest researchers.
According to the study by Oxford University's Department of Psychiatry, the relationship between bipolar disorder and violence largely came down to substance abuse.
AdvertisementThe study examined the lives and behaviour of 3,700 people in Sweden who had been diagnosed with bipolar disorder, commonly known as manic depression.
The team, led by consultant forensic psychiatrist Seena Fazel, compared the experiences of the patients with some 4,000 siblings of people with bipolar disorder and a further group of 37,000 people selected from the general population.
They found that the rates of violent crime among people who were mentally ill and abused substances were no different to those among the general population who abused substances.
"Most of the relationship between violent crime and serious mental illness can be explained by alcohol and substance abuse," the BBC quoted Fazel as saying.
He said that if the substance abuse was taken away, the illness itself had a "minimal" or non-existent role in violence.
"It's probably more dangerous walking outside a pub on a late night than walking outside a hospital where patients have been released," he said.
The study said that people with bipolar disorder were 10 times more likely to abuse drugs or alcohol than those in the overall population because they tended to turn to substances to counter the effects of their medication or to get other relief from their symptoms.
A previous paper on schizophrenia, written by several of the same researchers, came to similar findings.
The findings of both studies support the view of mental health charities who argue that the stigma attached to illnesses is not justified by medical evidence.
Paul Farmer of the mental health charity Mind, said the research would reassure people with severe illnesses such as bipolar disorder and schizophrenia.
"The link between mental illness and violence is often grossly exaggerated when in fact people with mental health problems are far more likely to be the victims of crime than the perpetrators "This kind of stigma damages lives," he said.
The findings were published in the Archives of General Psychiatry.