Levothyroxine sodium is a medication taken by people who have hypothyroidism, or an underactive thyroid. Levothyroxine sodium is a man-made form of thyroid hormone that replaces the hormone that the body is not able to make. It can also be used to decrease the size of a thyroid gland that is too big (called a goiter).
Levothyroxine sodium comes in two forms. The tablet form is taken by mouth every day. The IV or intravenous form of this medicine is only given in hospitals in an emergency situation.