Synthroid is a replacement for a hormone normally produced by your thyroid gland to regulate the body’s energy and metabolism. Levothyroxine is given when the thyroid does not produce enough of this hormone on its own.
Synthroid treats hypothyroidism (low thyroid hormone). Synthroid is also used to treat or prevent goiter (enlarged thyroid gland), which can be caused by hormone imbalances, radiation treatment, surgery, or cancer. Synthroid may also be used for purposes not listed in this medication guide.