Taking certain prescription drugs, including opioids and anti-anxiety drugs known as benzodiazepines, appears to be linked with an increased risk of committing homicide, a new study suggests.

The researchers said they were surprised that painkillers were linked with an increased risk of homicide, according to CBS Atlanta.

The study by Finnish researchers included 959 males and females ages 13 to 88, who were all convicted of homicide. They compared each person in the study with 10 other people of the same age and gender who had not committed homicide, and who lived in the same town.

The researchers found taking opioid painkillers was associated with a 92 percent increased risk of committing homicide, while tranquilizers were associated with a 45 percent increased risk. Antidepressants were linked with a 31 percent increased homicide risk.

“It has been repeatedly claimed that it was the antidepressants used by the persons who committed these massacres that triggered their violent behavior,” lead researcher Jari Tiihonen said in a news release. “It is possible that the massive publicity around the subject has already affected drug prescription practices.”

Tiihonen added, “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 study will appear in the journal World Psychiatry.