Paroxetine is a prescription medication that belongs to a class of drugs known as selective serotonin reuptake inhibitors (SSRIs). The drug is used to treat a number of conditions, including depression, obsessive-compulsive disorder (OCD), and post-traumatic stress disorder (PTSD). Paroxetine works by balancing the levels of a certain chemical (serotonin) in the brain. The medication comes in tablet and liquid form and is usually taken once a day. Examples of side effects associated with this drug include dry mouth, nausea, and insomnia. Paroxetine is sold under the brand name Paxil^®; generic versions of the medication are also available.