Cytomel 

Cytomel is made in the laboratory and is a form of the natural thyroid hormone triiodothyronine. It is given when the thyroid gland is not producing enough of this hormone on its own, to treat hypothyroidism (low thyroid gland hormone).
It is also given as part of medical tests for thyroid gland disorders. Likewise, it is also used in conjunction with surgery and radioactive iodine therapy in people with thyroid cancer.