MONDAY, Feb. 2, 2009 (HealthDay News) -- Mental illness alone is not a predictor of future violent behavior, but mental illness combined with substance abuse or dependence does increase the risk, according to U.S. researchers who analyzed data collected from nearly 35,000 people.
People who have a severe mental illness but no substance abuse or a history of violence weren't any more likely than any other person in the general population to be violent over a period of three years, the study found. But the risk for future violence reached the level of statistical significance when mental illness was combined with substance abuse.
Still, the mental illness/substance abuse combination only ranked ninth on the study's list of the top 10 predictors of future violence. The predictors, listed from first to tenth, were: age (younger people are more likely to commit violence); history of violence; gender (males are more prone to violence); history of juvenile detention; divorce or separation in the past year; history of physical abuse; parental criminal history; unemployment in the past year; mental illness with substance abuse; and victimization in the past year.
The findings appear in the February issue of the Archives of General Psychiatry.
"Our study shows that a link between mental illness and violence does exist, but it's not as strong as most people think," said study author Eric B. Elbogen, an assistant professor in the forensic psychiatry program at the University of North Carolina (UNC) at Chapel Hill School of Medicine.
"We found that several other factors -- such as history of past violence or substance abuse or a recent divorce or loss of one's job -- are much more predictive of future violence than mental illness alone. Only when a person has both mental illness and substance abuse at the same time does that person's risk of future violence outweigh anyone else's," Elbogen said in a UNC news release.
Study co-author Dr. Sally C. Johnson said the "findings challenge the perception that some people have, and which you often see reflected in media coverage, that mental illness alone makes someone more dangerous. Our study shows that this perception is just not correct."
The U.S. National Institutes of Mental Health has more about mental disorders.