The study is the first one of its kind in the world and found the greatest risk was associated with the use of painkillers and tranquillizing benzodiazepines, while anti-depressants were linked only to a slightly elevated risk.
Professor Jari Tiihonen’s research group analysed the use of prescription drugs of 959 persons convicted of a homicide. “It has been repeatedly claimed that it was the anti-depressants used by the persons who committed these massacres that triggered their violent behaviour,” he said.
“It is possible that the massive publicity around the subject has already affected drug prescription practices. 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.”
The newly published study analysed the pre-crime use of prescription drugs among all persons convicted of a homicide in Finland between 2003 and 2011. The registers used were the Finnish Homicide Database of the Institute of Criminology and Legal Policy, and the Finnish Prescription Register of the Social Insurance Institution of Finland, Kela.
After confounding factors were controlled for, the results show that the use of anti-psychotics was not associated with a significantly increased risk of committing a homicide, whereas the use of anti-depressants was associated with a slightly elevated risk (+31%), and the use of benzodiazepines (drugs used to treat anxiety and insomnia) with a significantly elevated risk (+45%).
The study further found that the highest increase in the risk of committing a homicide was associated with opiate painkillers (+92%) and anti-inflammatory painkillers (+206%). In persons under 26 years of age, the highest increase in the risk of committing a homicide was associated with opiate painkillers (+223%) and benzodiazepines (+95%). An increase in the risk by, for example, 100% means that the risk doubles. Although the use of intoxicants was present in the majority of the homicides, the differences between the drug groups could not be explained by simultaneous intoxicant use.
Read the study in full in the online version of the latest issue of World Psychiatry at DOI 10.1002/wps.20220.