If you examine all of the high-profile crimes that have happened any time recently, they share one thing; psychiatric medication. It was once common to ask someone who was acting bizarrely if they were 'off their meds' but it became more common to worry they are on them.

A new paper in The Lancet took a retrospective look at population data and think the fears about medication may be misplaced. The psychiatrists, led by Dr. Seena Fazel of Oxford University, used Swedish national health registries to study the psychiatric diagnoses, and any subsequent criminal convictions, in over 80,000 patients (40,937 men and 41,710 women) who were prescribed anti-psychotic or mood stabilizing medication from 2006 to 2009.

In the three years studied, 6.5% (2657) of the men, and 1.4% (604) of women were convicted of a violent crime. Compared with periods when participants were not on medication, violent crime fell by 45% in patients receiving anti-psychotics, and by 24% in patients prescribed mood stabilizers.  

The two types of medication are often combined, the researchers found no evidence that combining the drugs has any further effect on reducing violent crime, and for patients prescribed mood stabilizers, the medication was associated with reductions in violent crime only in male patients with bipolar disorder.

They conclude that people who use anti-psychotic medication (such as clozapine or risperidone) to treat psychiatric illness are nearly half as likely to commit a violent crime compared to when they are not using such medication. The use of mood stabilizing drugs (such as lithium or carbamazepine) was also associated with a reduced rate of violent crime, although the reduction is less pronounced, and only in patients with bipolar disorder.

Anti-psychotic and mood stabilizing medication are used to treat a variety of disorders, but are most commonly associated with the treatment of schizophrenia, bipolar disorder, and related disorders that affect up to 2% of the general population. Although evidence suggests that people who use these medications are at less risk of relapse and re-hospitalization for their illness, until now, there has been very little evidence for these drugs' effects on real-world adverse outcomes, such as reducing violent behavior, despite increasing prescription rates in many countries.

Although anti-psychotic and mood stabilizing medications are generally associated with treatment of schizophrenia or bipolar disorder, the researchers found that many people in the study were prescribed these drugs for other disorders, such as depression or alcohol and drug misuse.  

According to Fazel, "Patients with psychiatric disorders are at risk of perpetrating violent acts, as well as being victims. Until now, we have not known whether antipsychotics and mood stabilizers reduce risks of violence. 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."

In a linked Comment, Professor Sheilagh Hodgins of Université de Montréal, Canada, and Karolinska Institutet, Stockholm, Sweden, writes that "[This] well executed study provides a basis for future clinical studies aiming to establish how anti-psychotics and mood stabilizers can be used to reduce aggressive behavior. The study illustrates again that de-identified data from national registers that were established for administrative reasons can be used by epidemiologists to identify potential strategies to reduce health-related social problems."

That's good news, if it holds up. Medication will no longer be exculpatory for criminals and they can go back to being treated like criminals again.