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. 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. 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. 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. Levoxyl and Synthroid are brand names for the drug levothyroxine. Both medications contain the same active ingredient, levothyroxine, but they contain different inactive ingredients. Synthroid (levothyroxine) is a brand-name prescription drug that’s used to treat hypothyroidism and suppress TSH. Learn about side effects, dosage, 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). 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). 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. 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.