Thyroid hormone drugs are natural or synthetic preparations containing Tetraiodothyronine (T4, levothyroxine) Sodium or Triiodothyronine (T3, liothyronine) Sodium or both. T4 and T3 are produced in the human thyroid gland by the iodination and coupling of the amino acid tyrosine. T4 contains four iodine atoms and is formed by the coupling of two molecules of Diiodotyrosine (DIT). T3 contains three atoms of iodine and is formed by the coupling of one molecule of DIT with one molecule of Monoiodotyrosine (MIT). Both hormones are stored in the thyroid colloid as thyroglobulin. Thyroid hormone preparations belong to two categories: natural hormonal preparations derived from animal thyroid, and synthetic preparations.
The thyroid hormone, Thyroxine (T4) is a tyrosine-based hormone which is produced by the thyroid gland. Synthetic versions of this hormone are used to make up for a lack of naturally produced Thyroxine and increase the rate of metabolism. Artificially made thyroid hormone improves the symptoms of hypothyroidism (underactive thyroid) and speeds the rate of metabolism in those who suffer from the disease. Thyroid hormones may also be used to treat goiter (enlarged thyroid gland) and certain types of thyroid cancer.