The sodium salt form of liothyronine, a synthetic form of the levorotatory isomer of the naturally occurring thyroid hormone triiodothyronine (T3). Liothyronine sodium binds to nuclear thyroid receptors which then bind to thyroid hormone response elements of target genes. As a result, liothyronine sodium induces gene expression that is required for normal growth and development. Liothyronine sodium is more potent and has a more rapid action than thyroxine (T4). or A drug that is used to treat certain thyroid (a gland located near the voice box) conditions. It is also being studied in the treatment of thyroid cancer. Liothyronine sodium is made in the laboratory and is a form of the thyroid hormone triiodthyronine (T3). Also called Cytomel and Triostat.