Paroxetine is a prescription medication that is used to treat depression, obsessive-compulsive disorder (OCD), social anxiety disorder, and other conditions. The medicine belongs to a class of drugs known as selective serotonin reuptake inhibitors (SSRIs). Paroxetine works by blocking the reuptake of a chemical (serotonin) in the brain. The drug comes in tablet and suspension (liquid) form and is usually taken once a day. Examples of side effects that may occur with paroxetine include ejaculation problems, nausea, and insomnia.