L-thyroxine is the major hormone derived from the thyroid gland. It is synthesized via the iodination of tyrosines (monoiodotyrosine) and the coupling of iodotyrosines(diiodotyrosine) in the thyroglobulin. Thyroxine is released from thyroglobulin by proteolysis and secreted into the blood. Thyroxine is peripherally deiodinated to form triiodothyronine that exerts a broad spectrum of stimulatory effects on cell metabolism. It is mainly used for the treatment of hypothyroidism, goiter, chronic lymphocytic thyroiditis, myxedema coma, and stupor[1].