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How To Interpret That Study Linking Violence And Antidepressants

It doesn't necessarily mean what you think.

Young adults who take selective serotonin reuptake inhibitors, a widely prescribed type of antidepressant that includes brands like Prozac and Paxil, may be more likely to commit violent crimes, according to a study published in the journal PLOS Medicine in September.

The study found that young people between the ages of 15 and 24 were 43 percent more likely to commit a violent crime while using antidepressants and were also more likely to have non-violent convictions and arrests, as well as to suffer non-fatal accidents and have problems with alcohol. By contrast, there was no statistically significant association between violent crime and antidepressant use for adults ages 25 and older.

Paradoxically, young adults who took lower doses of the medication were more likely to be violent than those who took higher SSRI doses. Still, study author and University of Oxford senior research fellow Seena Fazel explained that the study results didn't rule out a smaller risk of increased violence among young adults who took moderate or high doses of SSRI antidepressants.

More studies, more conflicting results

The link between SSRI use and violence is controversial turf, and previous studies have yielded conflicting results. A 2010 PLOS One study that used data from the U.S. Food and Drug Administration found that SSRI use was associated with increased violence, for example, while a study published the same year in the Journal of Policy Analysis and Management reported exactly the opposite.

Unlike past analyses, the new study used what's called "within-individual design." This means the study compared the rate of violent crime when an individual was taking an SSRI antidepressant to the rate of violent crime in the same person while not taking the drug. In other words, it compared people to themselves, which minimized the impact of genetics and lifestyle choices.

The study, which included 856,493 individuals prescribed SSRIs in Sweden over the course of four years, defined violent crime as conviction for "attempted, completed, and aggravated forms of homicide, manslaughter, unlawful threats, harassment, robbery, arson, assault, assault on an official, kidnapping, stalking, coercion, and all sexual offenses."

Why is there an increased risk of violence among younger adults?

Taking medication incorrectly is one possible hypothesis for the association between younger people and violence. "Non-adherence may be more of a problem in younger people," Fazel said. Another, according to Fazel, is that the effects of withdrawal and the link between alcohol intoxication and misuse among younger people may be stronger than among older adults, although he noted that the study did not specifically examine any of these factors.

Previous research has shown that adolescents may react differently to antidepressants than adults, according to the National Institutes of Mental Health. In fact, a study published in the British Medical Journal in September linked the antidepressant paroxetine to self-harming and suicidal behaviors in adolescents, a group for which the drug was previously thought to be safe and effective.

The study comes with major caveats

The researchers were careful to note that association between antidepressant use among young adults and violent crime does not prove causation. Factors other than taking antidepressants, such as increased drug or alcohol use while taking medication or the worsening of psychological symptoms, could have played a role in the recorded uptick of violence among the young adults in the study.

Another challenge the researchers addressed and adjusted for in their findings was reverse causality, or the possibility that individuals who committed violent crimes used antidepressants to cope with the anxiety and stress of arrest.

And importantly, there's more research that still needs to be done.

"Around three-quarters of our sample were not clinically depressed according to specialist assessments," Fazel said. "Understanding the indications for the remaining three-quarters and whether their response to medication is different would be another area for future research."

The public should also be careful to keep the new study in perspective, and to avoid perpetuating the myth that individuals who suffer from mental illness are a violent group, which is far from the case. The reality is that people with severe mental illness are 10 times more likely to be the victim of a crime than the general population, a telling statistic that's often ignored by news media outlets and popular culture.

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