Cytomel (liothyronine sodium) Tablets contain liothyronine (L-triiodothyronine or L T3), a synthetic form of a natural thyroid hormone, and is available as the sodium salt. Twenty-five mcg of liothyronine is equivalent to approximately 1 grain of desiccated thyroid or thyroglobulin and 0.1 mg of L-thyroxine