The highest risk was among people who were aged 26 or younger and who were taking an opiate painkiller; they were four times more likely to become a killer, and the risk almost doubled if they were taking a benzodiazepine.
But the risk was almost as great in any age group if they were taking an anti-inflammatory painkiller, some of which are available without a prescription; the drugs quadrupled the risk of someone becoming a killer.
Researchers from the University of East Finland made the connection between the drugs and homicidal activity after they analysed the drug-taking history of 959 people who had been convicted of murder. They looked at their drug-taking before they had committed a crime and again afterwards.
Surprisingly, the expected suspects-the antipsychotics and antidepressants-seemed to have only a minimal effect. Of the real culprits, the benzodiazepines seemed to have been prescribed in high doses for long periods, and they can weaken our ability to control impulses. Painkillers affect emotional processing, say the researchers.
(Source: World Psychiatry, 2015; June 2015; doi: 10.1002/wps.20220)