Many countries around the world have seen a dramatic decline of violent crimes in the past several years. In the United States, crime rates dramatically fell since the 1990's and although the reason behind this remains a mystery, there has been no shortage of theories that attempt to explain the reduction in crime rates.

Among the possible explanations include the increased number of law enforcement officers, reduction of lead exposure in children and even the legalization of abortion. A new study, however, points to the use of antipsychotic drugs among mentally ill patients as one possible reason to the drop in violent crime rates.

In a new study published in The Lancet May 8, Seena Fazel from the Oxford University in U.K and colleagues sought to establish an association between the use of stabilizers and antipsychotic medications, which are used for treating patients with schizophrenia, bipolar disorder and similar psychiatric problems, and the rate of violent crimes committed by individuals with mental health disorders.

By using data from Swedish national health registries, the researchers examined the psychiatric diagnoses and subsequent criminal convictions of 40,937 men and 41,710 women prescribed with mood stabilizers and antipsychotic medications from 2006 to 2009.

Within the span of the study period, 6.5 percent of the men and 1.4 percent of the women were convicted of violent crimes. The rate of violent crimes such as assault, sexual offense and robbery, however, dropped by 45 percent in patients who were actively taking antipsychotic medications. The number of conviction also dropped by 24 percent in patients prescribed with mood stabilizers.

"In addition to relapse prevention and psychiatric symptom relief, the benefits of antipsychotics and mood stabilisers might also include reductions in the rates of violent crime," the researchers concluded.

Fazel said they were not able to determine why the medications lowered the violent crime rates committed by mentally ill patients but said it is possible that the drugs have treated psychosis itself.

National Institute of Mental Health (NIMH) director Thomas Insel noted that individuals who suffer from severe mental illness can be up to three times more likely to be violent than most people. Treating their condition may have helped reduced the likelihood of these patients to become violent. It isn't clear though whether the same effects would apply to other countries besides Sweden.

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