Synthroid is used for treating low thyroid hormone levels and certain types of goiters.

Levothroid (levothyroxine sodium) is a replacement for a hormone that is normally produced by your thyroid gland to regulate the body’s energy and metabolism used to treat hypothyroidism (low thyroid hormone). Levothroid is also used to treat or prevent goiter (enlarged thyroid gland), which can be caused by hormone imbalances, radiation treatment, surgery, or cancer.