Novel uses of thyroid hormones in patients with affective disorders

Hormones of the thyroid axis have been used to treat patients with any of several mental illnesses. However, in recent decades interest has focused almost exclusively on depression, though thyroid hormones, mainly thyroxine (T4), are used with lithium in rapid cycling bipolar disorder, a condition in which depression and mania rapidly alternate. In depression L-triiodothyronine (T3) has been used in preference to T4 because of its rapid onset and offset of action. In women starting treatment, T3 hastens the onset of therapeutic action of standard antidepressant drugs. It fails to do so in depressed men, who anyway respond faster than women to standard antidepressants. Standard drugs fail to produce satisfactory improvement in one-quarter to one-third of depressed patients. Then, in both men and women, T3 converts about two-thirds of drug failures to successes in rapid fashion. Lithium, which has antithyroid properties, produces a similar conversion rate. The majority of depressed patients are grossly euthyroid, but many show one or another subtle change in thyroid axis activity. However, the thyroid state of patients has not been matched systematically with their response to thyroid hormone augmentation. It seems likely that a tendency toward hypothyroidism can predispose to depression, but when depression occurs in a euthyroid patient, the thyroid axis is often invoked in the process of restitution.