The Thyroid Axis and Depression

Hypothyroidism may give rise to frank depression that usually responds to thyroxine therapy. Depressed subjects with subclinical hypothyroidism and/or autoimmune thyroiditis should probably also be treated similarly. Most patients with depression, although generally viewed as chemically euthyroid, have alterations in their thyroid function including slight elevation of the serum thyroxine (T4), blunted thyrotropin (TSH) response to thyrotropinreleasing hormone (TRH) stimulation, and loss of the nocturnal TSH rise. These changes are generally reversed following alleviation of the depression. The role of adjuvant triiodothyronine (T3) treatment in resistant depression has not been established, but the data suggest that it will be beneficial in about 25% of cases. However, controlled trials to establish this approach are needed. The underlying mechanism leading to the beneficial response from T3 is unknown, but may reflect brain hypothyroidism in the context of systemic euthyroidism. The hypothalamus in cult...