You’ve probably heard the rumors, spreading like oil on water, when a well-publicized murderer, considered an even-tempered person by friends, neighbors, and co-workers, happened to be taking a psychiatric drug at the time. Did the medication somehow prompt the sudden violence? In a first-ever study, Finnish researchers discovered the use of drugs affecting the central nervous system are indeed linked to an increased risk of committing a homicide.

Painkillers and some benzodiazepines pose the greatest risk, they say, while antidepressants are associated with only a slightly elevated risk.

“I think that these chemical substances affect the impulse control of the person,” Dr. Jari Tiihonen, lead author and a professor, told Medical Daily. “The only surprising result was that painkillers also increase the risk.”

Investigating the Issue

While past studies have examined information concerning the side effects of antidepressants in particular, Tiihonen's work compared data on a range of psychotropic medications. For the study, Tiihonen and his colleagues analyzed the pre-crime use of prescription drugs among those convicted of a homicide in Finland between 2003 and 2011. They used national databases containing both prescription drug use as well as criminal activity. The researchers matched each offender with 10 controls of the same gender, age, and home municipality.

“On the basis of our results, benzodiazepines and painkillers, but not antidepressants are linked to an significantly higher risk,” Tiihonen told Medical Daily.

Specifically, antidepressants were associated with a 31 percent elevated risk, benzodiazepines (drugs used to treat anxiety and insomnia) with a 45 percent elevated risk, opiate painkillers with a 92 percent elevated risk, and anti-inflammatory painkillers with a 206 percent risk. To understand what these percentages mean, an increase in risk by 100 percent, for example, would double the overall risk.

In many cases, benzodiazepines had been prescribed in very high doses and for a long period of time. For some time, scientists have known that benzodiazepines may weaken impulse control, while painkillers may affect emotional processing.

The median age of offenders was 36.3 years, about 88 percent were males, under four percent had more than one victim, and about 79 percent were intoxicated by alcohol, while five percent had taken an illicit drug. Despite the high use of intoxicants, the researchers say the differences between drug groups could not be explained away by simultaneous use of alcohol or other drugs.

“I’d be interested to see if someone can replicate these findings in other countries,” Tiihonen said. He acknowledged the difficulties in doing so. Not many countries in the world, for instance, have the nationwide databases necessary. Also, in some countries, such as Colombia, the homicide rate is high due to organized crime.

Such murders are premeditated deeds, whereas “in developed countries, a large prop of homicides are impulsive deeds,” Tiihonen explained. Premeditated crime rates would likely not be affected by the use medication.

Source: Tiihonen J, Lehti M, Aaltonen M, Kivivuori J, Kautiainen H, Virta L, Hoti F, Tanskanen A, Korhonen P. Psychotropic drugs and homicide: a prospective cohort study from Finland. World Psychiatry. 2015.