Tricyclic antidepressants (abbreviation TCA) are a class of antidepressant drugs first used in the 1950s. They are named after the drugs' molecular structure, which contains three rings of atoms (compare tetracyclic antidepressant).

Example compounds

The first tricyclic antidepressant discovered was imipramine, which was discovered accidentally in a search for a new antipsychotic in the late 1950s.
Antidepressant drugs in the tricyclic drug group (along with their actions as listed in MeSH) include:

Note: Other sources suggest that most of the tricyclics combine adrenergic and serotonergic effects to some degree. This is often reported as selectivity ratios. Some of the above, in order from most selective for nor-epinephrine to most selective for serotonin: lofepramine, nortriptyline, amitriptyline, imipramine, clomipramine.

Amine classification

Tricyclics are sometimes classified as tertiary amines and secondary amines. In general, the tertiary amines boost serotonin as well as nor-epinephrine (adrenergic) and produce more sedation, anticholinergic effects, and orthostatic hypertension.[2] The secondary amines act primarily on nor-epinephrine and tend to have a lower side-effect profile[3].

Tertiary amines include: amitriptyline, imipramine, trimipramine, doxepin, clomipramine, and lofepramine.

Secondary amines include: nortriptyline, desipramine, protriptyline, and amoxapine.