EFFECT OF ANTIDEPRESSANT MEDICATION ON MORNING AND EVENING THYROID-FUNCTION TESTS DURING A MAJOR DEPRESSIVE EPISODE

Background: This study sought to determine whether changes in thyroid function that may occur during antidepressant treatment are related to a direct effect of the drug on the thyroid axis or to a change in cli nical state. Methods: Morning and evening thyroid function was evaluat ed in 30 euthyroid inpatients who met DSM-IV criteria for major depres sive episode, by determination of free triiodothyronine, free thyroxin e, and thyrotropin levels before and after 8 AM and 11 PM protirelin c hallenges (200 mu g intravenously), on the same day. Results at baseli ne were compared with those after 1 month of antidepressant treatment with either amitriptyline hydrochloride, fluoxetine hydrochloride, or toloxatane. Results: Clinical efficacy and effects on thyroid function did not differ across the 3 antidepressant drugs. Compared with pretr eatment values, significant reductions in basal serum 8 AM free thyrox ine, 11 PM free thyroxine, and 8 AM free triiodothyronine levels and i ncreases in 11 PM maximum increment in plasma thyrotropin level and th e difference between 11 PM and 8 AM maximum increment in plasma thyrot ropin values were observed in responders (n = 11) but not in partial r esponders (n = 6) or nonresponders (n = 13). Moreover, nonresponders e xhibited lower pretreatment 11 PM thyrotropin values (basal and maxima l increment above basal) than responders. Conclusions: The results sug gest that (1) changes in thyroid function are related to clinical reco very rather than to a direct effect of the antidepressant drug and (2) patients with the lowest pretreatment evening thyrotropin secretion h ave the lowest rate of antidepressant response, and this may contribut e to treatment resistance.