Schizophrenics are more likely to be convicted of crimes than non-schizophrenics, new research suggests.

Australian investigators found that, over a 25-year period, 21.6 percent of a study group of schizophrenics were convicted of a crime, compared with only 7.8 percent of a group of non-schizophrenics.

More than 8 percent of schizophrenics committed violent crimes, versus less than 2 percent of non-schizophrenics.

Over the same time period, the rate of drug abuse among schizophrenics markedly increased, going from 8.3 percent of people first diagnosed with the disorder in 1975 to 26.1 percent of those diagnosed in 1995.

Furthermore, schizophrenics with drug problems were more likely than other schizophrenics to also be convicted of a crime, the authors write in the American Journal of Psychiatry.

These findings show that treatment of schizophrenia needs to go beyond simply prescribing the drugs that mask its symptoms, Dr. Paul Mullen of Monash University and the Victorian Institute of Forensic Mental Health in Victoria, Australia told Reuters Health.

Mental health services need to think about “improving the social situation and social functioning of those with this illness, reducing and, if possible, removing substance abuse,” Mullen said.

Mullen and his team reviewed the criminal records of 2861 people diagnosed with schizophrenia between 1975 and 1995, and compared them to the same number of non-schizophrenics from similar backgrounds.

More than 17.5 percent of schizophrenics were diagnosed with a drug or alcohol problem, meaning they had been convicted of a substance-related offense, or received a formal diagnosis of a substance abuse disorder.

Most of the violent crimes that convicted schizophrenics involved robbery with violence. Four schizophrenics were convicted of murder.

Mullen explained that there are likely a variety of factors influencing the high rate of criminal activity among schizophrenics, such as their environment, drug use, the personality changes that are brought on by the illness, and the symptoms of schizophrenia. “I think there will be no single cause,” he said.

Mullen added that although most crimes are not committed by schizophrenics, proper treatment of people with schizophrenia may be “the most cost effective and socially beneficial” way to lower criminal activity, he noted.

“Proper management of those with schizophrenia would improve the lives of sufferers and make our communities a safer place,” Mullen added.

SOURCE: American Journal of Psychiatry, April 2004.