Thyroxine (T4) (T4)

Levothyroxine is the synthetic levo-isomer form of thyroxine (T4), a principal hormone produced by the thyroid gland. It functions as a prohormone for triiodothyronine (T3), its more active metabolite, and is essential for normal metabolism, growth, and neurological development. Levothyroxine is used primarily as a replacement therapy in hypothyroidism (both congenital and acquired), as well as for thyrotropin suppression in certain thyroid cancers. It does not act as a receptor, enzyme, or transporter, but replaces natural hormone and exerts effects via conversion to T3 and activation of nuclear thyroid hormone receptors. It is one of the most prescribed medications worldwide, though inappropriate use and over-replacement can pose significant health risks[1][2][3][4][5][6].

Other names

LevothyroxineL-thyroxineT43,3',5,5'-Tetraiodyl-L-thyronineL-thyroxine sodium saltLT4

Thyroxine (T4) is a prohormone that is converted to triiodothyronine (T3), the active form. T3 binds to nuclear thyroid hormone receptors to regulate gene transcription and protein synthesis, leading to increased metabolic rate, oxygen consumption, and energy use[1][3][5].