Levothyroxine, a thyroid hormone, is used to treat hypothyroidism, a condition where the thyroid gland does not produce enough thyroid hormone.Levothyroxine is also used to treat congenital hypothyroidism (cretinism) and goiter (enlarged thyroid gland). Synthroid (levothyroxine) treats hypothyroidism (low thyroid hormone) and different types of goiters (enlarged thyroid gland). Includes Synthroid side effects, interactions and indications. Along with its needed effects, levothyroxine (the active ingredient contained in Synthroid) may cause some unwanted effects. Although not all of these side effects may occur, if they do occur they may need medical attention. Synthroid (levothyroxine sodium) and Tirosint (levothyroxine sodium) are synthetic compounds identical to T4 (levothyroxine) produced by the human thyroid gland used to treat hypothyroidism due to many causes (for example: thyroid removal, thyroid atrophy, functional T4 deficiency, radiation treatment of the thyroid, and other causes). Levothyroxine is a synthetic thyroid hormone used to treat hypothyroidism, a condition in which the thyroid gland doesn't produce enough thyroid hormone. Learn about Synthroid (Levothyroxine Sodium) may treat, uses, dosage, side effects, drug interactions, warnings, patient labeling, reviews, and related medications. Synthroid is a medication used in the treatment of thyroid gland pathology. It effectively restores thyroid function, normalizing patient condition and improving their quality of their life. Side Effects. See also Precautions section. Hair loss may occur during the first few months of treatment. This effect is usually temporary as your body adjusts to this medication. Armour Thyroid is a natural desiccated thyroid extract for treating hypothyroidism. Used for over a century, this type of thyroid medication can cause some serious side effects, such as lack of. For adult hypothyroidism, levothyroxine is started at 12.5-125 mcg/day administered orally. Starting doses and dose changes may differ with individual patients based upon age, the presence of cardiovascular disease, the development of tolerance (reduced effectiveness with continued use), side effects to the medication, and blood levels of.