Association between SSRI use and violent crime could be explained by poor adherence

An association between the use of a class of antidepressant known as selective serotonin reuptake inhibitors (SSRIs) and violent crime in patients aged 15–24 years has been found by researchers in Sweden and the UK. The same association was not seen in patients aged 25 years and over, and no causal link has been made. 

The research team, led by Seena Fazel, professor of forensic psychiatry at the University of Oxford, compared data from 856,493 people who had been prescribed SSRIs between 2006 and 2009. They looked at the rate of violent crime while the subjects were prescribed SSRIs, and compared it with the rate of violent crime in the same individuals while they were not taking SSRIs. Matched data were taken from the Swedish Prescribed Drug Register and the Swedish national crime register. 

There was a significant association between SSRI use and convictions for violent crimes in people aged 15–24 years but not for older individuals. Increased risks were also found in the younger group for violent arrests, non-violent convictions and arrests, non-fatal accidental injuries and emergency contacts for alcohol problems. 

There are too many confounding factors at play in a study of this scale to make any causal link, but the findings mark an important step forward, says Fazel, whose Wellcome Trust-funded study was published in the open access journal PLoS Medicine
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on 15 September 2015. “There’s a signal here, but there isn’t an interpretation.” 

In some cases, he points out, a lower dose of the drug was associated with a higher risk of violent behaviour. It is possible, suggests Fazel, that a failure to adhere to the recommended prescription might lead to periods of withdrawal and subsequent extremes in behaviour. An individual “might take a few tablets, feel a bit better and then binge drink”, he says. 

The message, adds Fazel, is: “Take the prescribed course according to recommendations from your doctor.” Far from suggesting that patients should stop taking SSRIs, Fazel compares these drugs to antibiotics: “It’s important to take the agreed prescription.” 

Whether young adults are not so good at adhering to their prescriptions is difficult to determine. Although that is a possibility, the age range also covers the period during which, in previous studies, suicidal thoughts have been associated with SSRI use. “There might be something about younger people and how they respond to SSRIs,” he says. 

“If patients are getting side effects; [the drug] is making patients more hostile, they should go back to their doctors,” says Fazel. He suggests that information relating to these associations could be added to the drug labelling, so the patient or carer knows what to be aware of. “Having a fuller disclosure of the possible risks is important,” he adds. 

Ian Maidment, senior lecturer in clinical pharmacy at Aston University, says: “The risks identified by the study need to be validated through replication. At this stage, it can only be seen as a preliminary signal that SSRI antidepressants are associated with violent crime in certain populations.”

As with all cohort studies, there is the possibility that unknown confounders may not have been identified, he added. “But this study adds to the evidence that young people react differently to SSRIs compared with other age groups.”