Enhancement of Imipramine Antidepressant Activity by Thyroid Hormone

Twenty euthyroid patients with retarded depression were studied to determine the possible role of alterations in thyroid function in the etiology and treatment of depression. A battery of tests was administered regularly to measure change. Patients responded better to usual doses of imipramine when 25 µg. of L-triiodothyronine (T3) was administered daily. T3 was physiologically active, altering protein-bound iodine values and accelerating ankle reflex time. A possible explanation, based on relevant data from animal experiments, is that imipramine may elevate effective biogenic concentration, while T3 increases receptor sensitivity.