The Swedish and Finnish researchers behind the study were interested in investigating whether there was any scientific basis for the claim that psychotropic drugs can cause violent behavior.
The Swedish and Finnish researchers behind the study were interested in investigating whether there was any scientific basis for the claim that psychotropic drugs can cause violent behavior. This claim has been debated following massacres committed by young people in schools and other public places in the US and Finland.
"It has been repeatedly claimed that it was the antidepressants used by the persons who committed these massacres that triggered their violent behavior," explains study author Prof. Jari Tiihonen. "It is possible that the massive publicity around the subject has already affected drug prescription practices."
Prof. Tiihonen states that the following criteria must be fulfilled to properly investigate a proposed link between drug use and risk committing a crime:
- The sample needs to be representative
- The reason for using the drug needs to be taken into consideration
- The effect needs to be controlled for
- The effects of any other drugs and intoxicants used simultaneously also need to be considered.
The team analyzed data - from the Finnish Homicide Database of the Institute of Criminology and Legal Policy and the Finnish Prescription Register of the Social Insurance Institution of Finland - on the use of prescription drugs among 959 convicted murderers, prior to committing their crime, in Finland during the period 2003-2011.
The researchers found no significant association between use of antipsychotics and increased risk of committing a homicide. However, a slightly increased risk of committing a homicide (31% increased risk) was associated with antidepressant use.
Benzodiazepines and painkillers linked with greatest increased risk for homicide
Use of benzodiazepines to treat anxiety and insomnia was associated with a significantly increased risk (45% increase in risk) of committing a homicide, while the greatest increased risk was associated with opiate painkillers (92% elevated risk) and anti-inflammatory painkillers (206% increased risk).
In people under the age of 26, there was a 95% increased risk of committing a murder while using benzodiazepines, and a 223% increased risk of this crime among users of opiate painkillers.
To put this into context, an increase in risk of 100% means that the risk is doubled.
Prof. Tiihonen says that in many of the homicide cases, the person who committed the crime had been prescribed high doses of benzodiazepines for long periods of time:
"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."
In 2008, a study from the University of Manchester in the UK found that alcohol and drug misuse were linked with a greater risk of homicide. Of the 58 patient homicides recorded during the study period, a history of alcohol abuse was observed in 41, while 45 of those who had committed a murder had a history of substance misuse.