RESUMO
Synthetic thyroxine has replaced animal thyroid gland extract as the preferred drug in chronic thyroid hormone replacement. Synthetic thyroxine monotherapy is used to treat overt primary and secondary hypothyroidism, and some cases of subclinical hypothyroidism. In addition, thyroid-stimulating hormone suppressive therapy with thyroxine is a component of the chronic treatment for differentiated thyroid carcinoma. Liothyronine, however, is conventionally for short-term usage, including thyroid hormone withdrawal preparation for radioactive iodine scanning and treatment of differentiated thyroid carcinoma and some cases of myxoedema coma. On very rare occasions where patients are apparently intolerant of or unresponsive to thyroxine, liothyronine may be used chronically. However, there is controversy concerning the use of alternative regimens of thyroid hormone, such as the use of thyroxine-liothyronine combination and thyroid extracts. Thyroid hormone has also been misused to promote weight loss and treat 'symptomatic' biochemically euthyroid patients. There is insufficient evidence to support the use of thyroid hormone to improve treatment response in depression and severe non-thyroidal illnesses.