Synthroid is a brand name for levothyroxine sodium. Synthroid should be used only by the patient for whom it is prescribed. While taking Synthroid, you need to take Synthroid because of a thyroid hormone deficiency, Synthroid can also be used to treat the enlargement of the thyroid glands. Synthroid is to be used only when clearly needed during pregnancy. Synthroid is a naturally occurring hormone produced by the thyroid glands. Side effects for this reason the correct dose of Synthroid is difficult to find. A brand name for levothyroxine sodium. Most of these problems disappeared when levothyroxine tablets were taken with water. Synthroid is the most commonly prescribed of all the thyroid supplements.