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. 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). Levoxyl and Synthroid are brand names for the drug levothyroxine. Both medications contain the same active ingredient, levothyroxine, but they contain different inactive ingredients. 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]. It may also be used to treat and prevent certain types of thyroid tumors. [4]. It is not indicated for weight loss. [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. 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). Synthroid (levothyroxine) is a thyroid hormone used to treat low thyroid hormone levels (hypothyroidism) in both children and adults. It's also used to treat a certain type of thyroid cancer. Find patient medical information for Levothyroxine (Levoxyl, Synthroid, Tirosint,and others) on WebMD including its uses, side effects and safety, interactions, pictures, warnings, and user. Take Synthroid once a day, every day, at the same time before breakfast. Only take Synthroid with water and on an empty stomach. Wait 30 minutes to 1 hour before eating or drinking anything other than water. Keep this cheat sheet handy for fast facts about Synthroid and how to take it the right way. Synthroid is an inactive T4 that requires conversion to active T3 in your tissues. If you have inflammation, gut issues, genetics that limit conversion enzymes, or endocrine-disrupting chemical exposure, this conversion fails and you remain hypothyroid despite normal labs.