People with schizophrenia may have a reputation for being involved in violent crime, but that seems to be valid only if they also have a problem with substance abuse, a study suggests.

Prior research has indicated that people with schizophrenia are up to six times more likely than people in the general population to commit violent crimes. In fact, current guidelines recommend that all schizophrenic patients should be evaluated for their propensity to commit these acts, Dr. Seena Fazel, from Warneford Hospital, Oxford, UK, and colleagues explain in their report in this week’s Journal of the American Medical Association.

To investigate further, they studied data on 8003 schizophrenia patients and 80,025 population “controls” who were followed from 1973 to 2006 for violent crime convictions.

The overall analysis showed that schizophrenia doubled the likelihood of being involved in violent crime. Further analysis, however, showed that most of the association was driven by a fourfold increase in the odds of committing one or more violent crimes among patients who also abused drugs.

Without substance abuse, the likelihood of violent crime was only 20 percent higher among people with schizophrenia than those in the general population.

These findings, the authors conclude, suggest that the current recommendation to perform violent risk assessment in all patients with schizophrenia, rather than just in those with substance abuse, may need to be revised.

SOURCE: Journal of the American Medical Association, May 20, 2009.