Selective Serotonin Reuptake Inhibitors, or SSRIs, are a type of medicine that helps people feel better when they’re dealing with depression or anxiety. They work by increasing the amount of a chemical in the brain called serotonin, which helps control mood, sleep, and emotions. 

Normally, after serotonin is used by the brain, it gets reabsorbed (or “reuptaken”). SSRIs stop this from happening too quickly, which means there’s more serotonin available to help improve mood and reduce anxiety. Doctors often prescribe SSRIs to treat depression, anxiety disorders, and other mood problems.