Does thyroid hormone have a role as adjunctive therapy in depression?

Depression is associated with abnormalities of the thyroid axis, but the role of thyroid hormone therapy is controversial. In patients presenting with depression, the thyroid status should be carefully evaluated since hypothyroidism can cause depression. Frank hypothyroidism should be treated in the usual fashion with L-thyroxine, which may reverse the depressive state. If subclinical hypothyroidism and/or autoimmune thyroiditis are present, T3 adjuvant administration (25 micrograms/day) should be seriously considered in patients resistant to tricyclic antidepressant (TCA) (and probably also) serotonin selective reuptake inhibitor (SSRI) medication. The possible efficacy of adjuvant T4 in reversing the depression of such subjects appears less than T3. In depressed patients with TCA or SSRI resistance and no evidence of hypothyroidism, the data available do not establish the therapeutic role of T3 in this situation. Multicenter controlled studies of T3 adjuvant therapy are required. The possible mechanisms through which T3 adjuvant therapy might be efficacious are discussed.