What is liothyronine? Liothyronine Sodium 25 mcg table is a synthetic form of a hormone that the thyroid normally produces to regulate energy and metabolism. It is given when the thyroid does not produce enough of this hormone. Liothyronine treats hypothyroidism (low thyroid hormone levels). It is also given as part of medical tests for thyroid disorders. Liothyronine is also used in...