Question: what is the difference between l-thyroxine and synthroid?
Answer: What is Synthroid (levothyroxine)? Synthetic thyroxine (T4) comes as brand-name Synthroid or generic levothyroxine. T4 is what is known as a “prohormone”; it's made by the thyroid gland and gets converted to the active hormone, T3, in other body tissues.