Antidepressants are one of the most commonly prescribed classes of medication world-wide. They are primarily used to treat depression, but can be used to treat other psychiatric disorders such as generalized anxiety disorder, social anxiety disorder, obsessive-compulsive disorder (OCD), anorexia, and bulimia. Although not specifically intended to treat pain, antidepressants have become a mainstay in the treatment of chronic pain.

Many people with chronic pain suffer from depression, but antidepressants can ease chronic pain whether or not there is underlying depression. The pain relieving properties of antidepressants are not very well understood. They may increase neurotransmitters, or chemical messengers, in the brain and spinal cord that decrease pain signals. Antidepressant pain-relieving effects are not immediate and may take several weeks to provide maximum benefit. Many people report moderate pain relief from antidepressants. Anti-seizure medications can be added to antidepressants if pain relief is incomplete.