Mental illness alone does not predict violence, study says

When crimes of violence are committed by people with mental illness, some wonder why more can't be done to prevent such horrifying acts. But the answer isn't so simple, a large study of multiple factors associated with violence concludes.

Mental illness by itself does not predict future violent behavior, researchers from the University of North Carolina at Chapel Hill School of Medicine report in tomorrow's Archives of General Psychiatry, echoing previous smaller studies. Only when it is combined with other problems -- substance abuse, stressors like the loss of a job or a spouse, and a history of violence -- is an increase in violence seen, the researchers found in a national survey of more than 34,000 people.

"I think the real important finding here is that just because someone has a mental illness, it does not mean they are going to act violent," said Donald Davidoff, director of neuropsychology at McLean Hospital. He was not involved in the study. "Mental illness alone is not a significant risk factor."

But people with both mental illness and substance abuse had a 10 times higher risk of being violent than people with mental illness alone.

"Because severe mental illness did not independently predict future violent behavior, these findings challenge perceptions that mental illness is a leading cause of violence in the general population," the authors wrote. "Still, people with mental illness did report violence more often, largely because they showed other factors associated with violence. Consequently, understanding the link between violent acts and mental disorder requires consideration of its association with other variables such as substance abuse, environmental stressors and history of violence."