SSRIs are a class of antidepressants designed to increase serotonin levels while causing as little disruption to the rest of the brain as possible. Fluoxetine (Prozac) was the first SSRI to come to market. The FDA approved fluoxetine in 1987, and other SSRIs soon followed. Sertraline (Zoloft) was approved in 1991, and paroxetine (Paxil) in 1992. By 2017, 12.3% of Americans over the age of 12 were taking antidepressants—that’s around 40 million people.