Levothyroxine (INN, USAN) or L-thyroxine is a synthetic thyroid hormone that is chemically identical to thyroxine (T4), which is naturally secreted by the follicular cells of the thyroid gland. It is used to treat thyroid hormone deficiency, and occasionally to prevent the recurrence of thyroid cancer. Like its naturally secreted counterpart, levothyroxine is a chiral compound in the L-form. The related drug dextrothyroxine (D-thyroxine) was used in the past as a treatment for hypercholesterolemia (elevated
cholesterol levels) but was withdrawn due to cardiac side effects. It is on the World Health Organization's List of Essential Medicines, a list of the most important medication needed in a basic health system.

Levothyroxine (INN, USAN) or L-thyroxine is a synthetic thyroid hormone that is chemically identical to thyroxine (T4), which is naturally secreted by the follicular cells of the thyroid gland. It is used to treat thyroid hormone deficiency, and occasionally to prevent the recurrence of thyroid cancer. Like its naturally secreted counterpart, levothyroxine is a chiral compound in the L-form. The related drug dextrothyroxine (D-thyroxine) was used in the past as a treatment for hypercholesterolemia (elevated
cholesterol levels) but was withdrawn due to cardiac side effects.

Levothyroxine is typically used to treat hypothyroidism, and is the treatment of choice for patients with hypothyroidism, who often require lifelong thyroid hormone therapy. It may also be used to treat goiter via its ability to lower thyroid-stimulating hormone (TSH), a hormone that is considered goiter-inducing. Levothyroxine is also used as interventional therapy in patients with nodular thyroid disease or thyroid cancer to suppress thyroid-stimulating hormone (TSH) secretion.

Levothyroxine is typically used to treat hypothyroidism,and is the treatment of choice for patients with hypothyroidism, who often require lifelong thyroid hormone therapy.It may also be used to treat goiter via its ability to lower thyroid-stimulating hormone (TSH), a hormone that is considered goiter-inducing.Levothyroxine is also used as interventional therapy in patients with nodular thyroid disease or thyroid cancer to suppress thyroid-stimulating hormone (TSH) secretion.