The physiological actions of thyroid hormones are developed predominantly by T3, nearly all of which (close to 80%) is derived from T4 by deiodination in peripheral tissues. Synthetic T4 is similar in chemical construction to your T4 generated within the human thyroid gland. Levothyroxine sodium has the molecular formula C15H10I4NNaO4· https://colettev085llg1.wikififfi.com/user