Paroxetine ( pər-AHK-sə-deen), sold under the brand name Paxil among others, is an antidepressant medication of the selective serotonin reuptake inhibitor (SSRI) class used to treat major depressive disorder, obsessive–compulsive disorder (OCD), panic disorder, social anxiety disorder, post-traumatic stress disorder (PTSD), generalized anxiety disorder, and premenstrual dysphoric disorder. It has also been used in the treatment of premature ejaculation, and hot flashes due to menopause. It is taken orally (by mouth).

Common side effects include drowsiness, dry mouth, loss of appetite, sweating, trouble sleeping, and sexual dysfunction. Serious side effects may include suicidal thoughts in those under the age of 25, serotonin syndrome, and mania. While the rate of side effects appears similar compared to other SSRIs and SNRIs, antidepressant discontinuation syndrome may occur more often. Use in pregnancy is not recommended, while use during breastfeeding is relatively safe. It is believed to work by blocking the reuptake of the chemical serotonin by neurons in the brain.

Paroxetine was approved for medical use in the United States in 1992 and initially sold by GlaxoSmithKline. It is on the World Health Organization's List of Essential Medicines. It is available as a generic medication. In 2022, it was the 92nd most commonly prescribed medication in the United States, with more than 7 million prescriptions. In 2018, it was in the top 10 of most prescribed antidepressants in the United States.