"Levothyroxine is a naturally occurring hormone important for normal energy and metabolism. Synthroid is the number one prescribed treatment for thyroid disease, in conditions where the thyroid gland. Synthroid is to be used only by the patient for whom it is prescribed. Synthroid is the number one prescribed treatment for thyroid disease, in conditions where the thyroid gland does not produce enough of thyroid hormone on its own, Synthroid is taken to replace the body's thyroid hormone."