Antidepressants are medications that have been approved to treat people diagnosed with depression, a psychiatric disorder characterized by symptoms such as extreme sadness, an inability to concentrate, insomnia, loss of appetite, helplessness and thoughts of death. Many of these drugs also are used in pain management.

Although the U.S. Food and Drug Administration (FDA) has not approved tricyclic antidepressants (TCAs) for use in pain relief, they are commonly prescribed to treat chronic pain conditions.

Many patients with chronic pain have depression as well, so the TCAs can help treat both conditions. These drugs are usually used to relieve depression by blocking the reuptake of the neurotransmitters norepinephrine and serotonin in the central nervous system. They relieve pain regardless of whether or not a patient also has depression. TCAs are not addictive.

For at least 40 years, scientists have known about the analgesic potential of antidepressants. As with all analgesic medications, scientists do not yet understand exactly how antidepressants help relieve pain.

Of the antidepressants, TCAs have the longest history of use in pain relief. It is believed that these drugs increase the number of neurotransmitters in the spinal cord that reduce pain signals. TCAs do not immediately relieve pain. It may take several weeks before the pain-reducing benefits of TCAs are experienced.

Among the other classes of antidepressants are selective serotonin and norepinephrine reuptake inhibitors (SSNRIs). The FDA has approved an SSNRI for relief of painful diabetic neuropathy.

The FDA in 2005 issued a public health advisory for antidepressant medications. Scientific studies found that some antidepressants increased the risk of suicidal thoughts in some people with major depressive disorders and other psychiatric disorders. The agency ordered warnings to be placed on medications.

Patients on antidepressants should be closely monitored for any worsening of their condition, suicidal thoughts or behaviors, or otherwise unusual behaviors.