Tricyclic antidepressants do not alter thyroid hormone levels in patients suffering from a major affective disorder.

Abnormalities of thyroid function have been associated with affective disorders, and treatment with thyroid hormones or drugs that alter thyroid hormone levels can change the course of an affective disorder. Therefore, we investigated the possibility that mood-altering effects of tricyclic antidepressants would be mediated by alterations in thyroid hormones (T3 and T4) levels. In a group of 11 patients with affective disorders, tricyclic antidepressants did not alter serum T3 and T4 levels. We conclude that the mood-altering potency of tricyclic antidepressants, and particularly their potency to induce rapid mood cycles, is not due to changes in total T3 and T4 serum levels.