Potentiation of antidepressant effects by L-triiodothyronine in tricyclic nonresponders

Six women and 6 men who were treated in double-blind fashion major depressive illness did not respond to imipramine or amitriptyline, 150-300 mg/day, during periods of 26-112 days. After the addition of 25 micrograms/day (10 patients) or 50 micrograms/day (2 patients) of L-triiodothyronine (T3), 9 patients showed statistically significant improvement in depression scores; in 8 patients the response was marked. Improvement generally began within 1-3 days and was noted in all aspects of the depressive syndrome; side effects were minimal. T3 did not change plasma levels of imipramine or desipramine or their ratio but did suppress serum thyroxine.