Treating psychiatric illnesses with antipsychotic drugs can greatly reduce the risk that a patient will commit a violent crime, researchers reported on Thursday.
Their study, published in the Lancet medical journal, adds weight to the argument that severely mentally ill people need to get diagnosed and treated.
Mental health experts agree that people with psychiatric illnesses such as schizophrenia are far more likely to become victims of violence than they are to hurt someone else. But Dr. Thomas Insel, director of the National Institute on Mental Health, also notes that people with severe mental illness are up to three times more likely than the general population to be violent.
The question has been whether treatment lowers these risks. One high-profile case is that of Jared Loughner, a schizophrenia patient who shot and killed six people in Arizona and wounded several more, including then-congresswoman Gabrielle Giffords.
Dr. Seena Fazel of Britain's Oxford University used a Swedish national database to find out. Sweden keeps careful medical records, and has similar rates of both mental illness and violence to the United States. The only exception is homicide, where the U.S. has much higher rates than just about every other country.
Fazel's team looked at the medical records of everyone born in Sweden between 1961 and 1990. "We identified 40,937 men and 41,710 women who were prescribed any antipsychotic or mood stabilizer between Jan 1, 2006, and Dec 31, 2009," they wrote. It worked out to about 2 percent of the population.
They looked at criminal records and the type of drug given. "We noted substantially lower rates of violent crime when any of the three classes of medication had been prescribed, specifically for antipsychotics and mood stabilizers," they wrote.
"In the three years studied, 6.5 percent (2,657) of the men, and 1.4 percent (604) of women were convicted of a violent crime. Compared with periods when participants were not on medication, violent crime fell by 45 percent in patients receiving antipsychotics, and by 24 percent in patients prescribed mood stabilizers," they added.
Violent crime was defined as murder, assault, robbery, threatening behavior, any sexual offense and arson.
Doubling up on the medications did not seem to help, something that may be important in making sure patients get the safest treatments possible, they noted.
They compared the patients against themselves, too, looking at times when they were on medications compared to times when they went without it. Again, patients were less likely to be violent when given drugs.
"By comparing the same people when they are on medication compared to when they are not, our study provides evidence of potentially substantial reductions in risk of violence, and suggests that violence is to a large extent preventable in patients with psychiatric disorders," Fazel said in a statement.