Venlafaxine, sold under the brand name Effexor among others, is an antidepressant medication of the serotonin-norepinephrine reuptake inhibitor (SNRI) class. It is used to treat major depressive disorder, generalized anxiety disorder, panic disorder, and social anxiety disorder. It may also be used for chronic pain. It is taken by mouth. It is also available as the salt venlafaxine besylate in an extended-release formulation (Venbysi XR).

Common side effects include loss of appetite, constipation, dry mouth, dizziness, sweating, insomnia, drowsiness and sexual problems. Severe side effects include an increased risk of suicide, mania, and serotonin syndrome. Antidepressant withdrawal syndrome may occur if stopped. There are concerns that use during the later part of pregnancy can harm the baby. How it works is not entirely clear, but it seems to be related to the potentiation of the activity of some neurotransmitters in the brain.

Venlafaxine was approved for medical use in the United States in 1993. It is available as a generic medication. In 2020, it was the 43rd most commonly prescribed medication in the United States with more than 15 million prescriptions.