Synthroid is a thyroid medicine that replaces a hormone normally produced by your thyroid gland to regulate the body's energy and metabolism. Synthroid is a prescription medicine used to treat hypothyroidism (low thyroid hormone). Levothyroxine is used to treat low thyroid activity and to treat or suppress different types of goiters. Learn about side effects, interactions and indications. Levothyroxine, also known as L-thyroxine, is a synthetic form of the thyroid hormone thyroxine (T 4). [4][7] It is used to treat thyroid hormone deficiency (hypothyroidism), including a severe form known as myxedema coma. [4] SYNTHROID® (levothyroxine sodium) tablets, for oral use is a prescription, man-made thyroid hormone that is used to treat a condition called hypothyroidism in adults and children, including infants. Overview: Levothyroxine is used as a replacement hormone therapy for people with low thyroid hormone levels, among other uses. Levothyroxine interacts with many medicines and health conditions. Levothyroxine is used to treat hypothyroidism, a condition where the thyroid gland does not produce enough thyroid hormone. This medicine is also used to help decrease the size of enlarged thyroid glands (also called a goiter). Medications such as anti-hypertensives, diabetic medications, and seizure medications are all included in this list. If at all possible it may be worth a look at your medication list to determine if you can consolidate medications or even change medications to see if it improves thyroid function. Learn about Synthroid (levothyroxine) usage and dosing. Read the latest news and reviews about the drug as well as potential side effects and popular alternatives. Synthroid (levothyroxine) is a brand-name prescription drug that’s used to treat hypothyroidism and suppress TSH. Learn about side effects, dosage, and more. Synthroid is a prescription medicine used to treat the symptoms of hypothyroidism and an enlarged thyroid gland (goiter). Learn about dosage, side effects, drug interactions, warnings, and more.