Levothyroxine sodium is a synthetic crystalline levothyroxine sodium (L-thyroxine). L-thyroxine is the principal hormone secreted by the normal thyroid gland. Chemically, L-thyroxine is designated as L-tyrosine, O- (4-hydroxy-3, 5-diiodophenyl) - 3,5-diiodo -, monosodium salt, hydrate. It is used in replacement or supplemental therapy in patients o...