The physiological actions of thyroid hormones are produced predominantly by T3, the vast majority of which (approximately 80%) is derived from T4 by deiodination in peripheral tissues. Synthetic T4 is identical in chemical composition into the T4 generated inside the human thyroid gland. Levothyroxine sodium has the molecular formulation C15H10I4NNaO4 https://lanerodpe.tinyblogging.com/the-smart-trick-of-200mg-ml-testosterone-that-no-one-is-discussing-83439311