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Tricyclic and tetracyclic antidepressants, also called cyclic antidepressants, are among the earliest antidepressants developed. They're effective, but they've generally been replaced by antidepressants that cause fewer side effects. However, cyclic antidepressants may be a good option for some people. In certain cases, they relieve depression when other treatments have failed.

Cyclic antidepressants are designated as tricyclic or tetracyclic, depending on the number of rings in their chemical structure — three (tri) or four (tetra).