Thyroid hormones in depressive disorders: a reappraisal of clinical utility

Centuries of clinical observation suggest a connection between thyroid function and behavior. Advances in neuroendocrinology of the hypothalamic-pituitary-thyroid (HPT) axis provide many techniques for examining the role of thyroid function in psychiatric disorders. HPT hypofunctioning may be especially relevant to the pathophysiology of major mood disorders, although the diagnostic specificity and prognostic value of its assessment remain tentative. Evidence that synthesis and actions of thyroid hormones in the brain may not parallel those in the periphery further complicates such assessments. Nevertheless, measures of HPT function show some promise of contributing to the clinical evaluation and treatment of depression. Research findings include an association of subclinical hypothyroidism with unsatisfactory responses to antidepressant treatment, evidence that triiodothyronine and thyroid-stimulating hormone may speed recovery in acute depression, and limited and inconsistent support for the effectiveness of exogenous thyroid hormones to augment antidepressants. Additional systematic and controlled studies comparing various types and doses of thyroid hormones are needed to establish their efficacy and safety. Of special interest would be studies that use contemporary diagnostic methods, assess thyroid function, and employ the newer, safer antidepressants.