liothyronine is a synthetic form of triiodothyronine (t3), a thyroid hormone used to treat hypothyroidism and myxedema coma. T3 is the metabolically active thyroid hormone, which causes feedback inhibition, and lowers elevated tsh levels. It increases metabolism in peripheral tissues and is indicated when there is an impaired conversion of t4 to t3 in peripheral tissues. It is also used as an augmentation strategy in treating major depressive disorder when used in combination with antidepressants.[1] it is marketed as the sodium salt under the brand