Certain painkillers and tranquilizers that affect the central nervous system have been linked for the first time with an increased risk of committing murder, in a new study published in the journal World Psychiatry.

The Swedish and Finnish researchers behind the study launched the research to settle a long-running scientific debate over suggestions that psychotropic drugs can cause violent behavior, in the way of mass killings in schools and other public places in the U.S. and Finland, Medical News Today reports.

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

For the study, Tiihonen and colleagues 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. They tracked the use of prescription drugs among 959 convicted murderers, prior to committing their crime, in Finland from 2003 to 2011.

The researchers found no significant association between use of antipsychotics and increased risk of committing a homicide. But the results did show a slightly increased risk of committing a homicide was associated with antidepressant and opiate painkiller use.

In people under the age of 26, there was a 95 percent increased risk of committing a murder while using benzodiazepines, and a 223 percent increased risk of homicide among users of opiate painkillers.

"Benzodiazepines can weaken impulse control, and earlier research has found that painkillers affect emotional processing,” Tiihonen explained. “Caution in prescribing benzodiazepines and strong painkillers to people with a history of substance abuse is advisable."