Levothyroxine is a synthetic form of thyroxine (T4), an endogenous hormone secreted by the
thyroid gland, which is converted to its active metabolite, L-triiodothyronine (T3). T4 and T3
bind to thyroid receptor proteins in the cell nucleus and cause metabolic effects through the
control of DNA transcription and protein synthesis. Like it's naturally secreted counterpart,
levothyroxine is a chiral compound in the L-form.