tricyclic antidepressant (TCA), any of a group of antidepressant drugs that contain three fused rings in their chemical structure and that potentiate the action of catecholamines. These drugs rapidly block the reuptake of amine neurotransmitters, but the exact mechanism of their effect is unknown because a period of time is required for the beneficial antidepressant effects to appear. The tricyclic antidepressants include a number of compounds, which may be grouped into four classes on the basis of chemical structure: dibenzazepines, dibenzocycloheptadienes, dibenzoxazepines, and dibenzoxepines. Besides their use to treat depression, various tricyclic antidepressants are used for other conditions, such as obsessive-compulsive disorder, panic disorder, and neurogenic pain.
