Researchers have identified a troubling side effect of a widely prescribed class of antidepressants -- they may make some patients more likely to commit violent crimes.
Data from Sweden show that young adults between the ages of 15 and 24 who had filled prescriptions for the drugs were more likely to be convicted of a homicide, assault, robbery, arson, kidnapping, sexual offense or other violent crime when they were taking the medications than when they weren't. The researchers found no link between antidepressant use and criminal activity for older patients.
The findings, published Tuesday in the journal PLOS Medicine, build on other evidence that the antidepressants – known as selective serotonin reuptake inhibitors, or SSRIs – work differently in the brains of adolescents and adults. For instance, several studies have shown that the drugs actually boost the risk of suicidal thoughts in children, teens and young adults, but not in older adults.
The link between SSRIs and crime is less clear. One analysis of trends in the U.S. found that the "great American crime decline" that began in the 1990s coincided with the emergence of SSRIs, including Prozac, Celexa, Paxil and Zoloft. But reviews of safety data submitted to the Food and Drug Administration have found that SSRI use was associated with an increased risk of violent behavior.
SSRIs help cells in the brain communicate with one another by making better use of a chemical called serotonin. This chemical is necessary for sending a message from one brain cell to another. Scientists believe that with more available serotonin, the brain circuits that control mood stand a better chance of functioning properly.
To get a clearer picture of the potential risks associated with SSRIs, researchers from the Karolinska Institute in Stockholm and the University of Oxford in England turned to national data from Sweden, where the government keeps track of prescriptions that are filled as well as convictions for crimes.
In Sweden, the criminal justice system treats people as adults once they turn 15. So the researchers examined records for nearly 8 million Swedes who were at least 15 years old in 2006. They found that more than 850,000 of them had been prescribed an SSRI sometime between 2006 and 2009. That amounted to 14.1% of all Swedish women and 7.5% of all Swedish men.
Among all of the people who got prescriptions for SSRIs, 1% of them were convicted of committing some type of violent crime between 2006 and 2009. The researchers focused on these 8,377 people and compared their criminal activity when they had an SSRI prescription to the periods when they did not.
The initial analysis found that the risk of a violent crime conviction was 19% higher when people were taking the antidepressants than when they weren't. The increase in risk was essentially the same when the researchers factored in the influence of other psychotropic drugs.
When they broke down the numbers according to age, they found that the risk was concentrated among the youngest group of people. For adults between the ages of 15 and 24, the risk of being convicted of a violent crime was 43% greater when they were taking an SSRI than when they weren't.
Then the researchers considered the men in this age group separately from the women. Among men, taking SSRIs was linked with a 40% increased risk of being convicted of a violent crime; among women, the risk increased by 75%, according to the study.
The study doesn't prove that the SSRIs were responsible for the observed increase in criminal violence among teens and young adults, the researchers said. However, it does add to evidence that "the adolescent brain may be particularly sensitive to pharmacological interference," they wrote.
Even if it turns out that the antidepressants do make young people more likely to commit violent crimes, does that mean doctors should stop prescribing them? The answer is not obvious, the researchers wrote. Dialing back on SSRIs may cause violence to go down, but then suicides may go up. "From a public health perspective," they wrote, it may be better to keep on using the drugs "as long as potential risks are disclosed."