Can Popping Pills Lead You to Kill?

Finnish researchers have discovered a link between an increased rate of committing homicide and the use of drugs that affect the central nervous system (CNS). Use of tranquilizing benzodiazepines and painkillers carries the highest association with committing homicide, while there was only a slightly greater risk for users of anti-depressants.

This research team believes that the link between homicide commission and drug use is impulse control or emotional processing. For example, researchers already believe that use of painkillers affects emotional processing while use of benzodiazepines weakens impulse control.

"I think that these chemical substances affect the impulse control of the person," Lead author of the study, Dr. Jari Tiihonen says. "The only surprising result was that painkillers also increase the risk."

Tiihonen and his research team analyzed data on 959 people convicted of homicide to assess their use of prescription drugs. The research was conducted in part to address the growing belief that use of psychotropic drugs like anti-depressants can cause violent behavior.

"It has been repeatedly claimed that it was the anti-depressants used by the persons who committed these massacres that triggered their violent behavior. It is possible that the massive publicity around the subject has already affected drug prescription practices," Tiihonen says.

This is the first study of its kind because it properly addresses various control factors in order to suss out the real link between the risk of committing a crime and drug use. The team used a representative sample, controlled for effects, and included assessment of the reasons for the drug use. Furthermore, this study focuses on a range of psychotropic drugs rather than just one drug or a set of anti-depressants.

"On the basis of our results, benzodiazepines and painkillers, but not antidepressants are linked to an significantly higher risk," Tiihonen says.

The team accessed a wealth of data to complete the study; sources include the Finnish Prescription Register of the country's Social Insurance Institution and the Finnish Homicide Database of the Institute of Criminology and Legal Policy. The data concerned the pre-offense drug use of those convicted of homicides in Finland between 2003 and 2011. Approximately 88 percent of the offenders were male, and the median age of the sample was 36.3 years. 79 percent of the offenders were under the influence of alcohol at the time of the offense, but the researchers do not attribute the differences in homicide rates from drug to drug to that intoxication.

Controlling for factors that might possibly confound the results, researchers found that the risk of committing homicide is elevated by 31 percent for anti-depressant users. Benzodiazepines, which are used to treat insomnia and anxiety, are associated with a 45 percent elevation in risk. Opiate painkillers carry a 92 percent elevation in risk, and use of anti-inflammatory painkillers correlate to a whopping 206 percent increased risk. For subjects younger than age 26, however, opiate painkillers have the highest increase in risk-223 percent, followed by benzodiazepines with a 95 percent increase in risk.

This means that within the entire group anti-inflammatory users were four times more likely to commit homicide; a risk increased by 100 percent means it is twice as likely to happen.

The researchers noted the findings support careful, restricted use of both benzodiazepines and painkillers. "Benzodiazepines can weaken impulse control, and earlier research has found that painkillers affect emotional processing. Caution in prescribing benzodiazepines and strong painkillers to people with a history of substance abuse is advisable."

Although it won't be an easy task due to lack of data in many areas, Tiihonen and the team hope that their work will be duplicated for countries around the world. He also points out that certain countries may have aberrant data for cultural reasons. For example, in countries that experience high murder rates associated with organized crime are less likely to show as strong a pattern because premeditation is not likely to be affected.

"I'd be interested to see if someone can replicate these findings in other countries. [Murders within the organized crime context are premeditated, but]. . .in developed countries, a large prop of homicides are impulsive deeds."