Health A-Z

Medical Content Created by the Faculty of the
Harvard Medical School

Hyperthyroidism

What Is It?

Hyperthyroidism means having abnormally high levels of thyroid hormones. Thyroid hormones, which are made by the thyroid gland in the lower front of the neck, regulate the body's energy. When levels of thyroid hormones are unusually high, the body burns energy faster and many vital functions speed up.

In most cases, hyperthyroidism is caused by the thyroid gland producing too much thyroid hormone. The three most common reasons for this are:

• Graves' disease, an immune-system disorder that causes the thyroid to release too much thyroid hormone. Graves' disease typically affects young women between ages 20 and 40, although about 12% of patients are men. Because Graves' disease is an inherited disorder related to genetic factors, thyroid disease tends to affect several people in the same family.

• A benign (noncancerous) thyroid tumor that secrets increased amounts of thyroid hormones in an uncontrolled manner

• Toxic multinodular goiter, a condition in which the thyroid gland is enlarged with many benign (noncancerous) thyroid tumors that secrete increased amounts of thyroid hormone

Very rarely, hyperthyroidism may be caused by the pituitary gland making too much thyroid-stimulating hormone (TSH), which causes the thyroid gland to produce too much thyroid hormone.

Certain types of thyroid inflammation, in the postpartum period or after viral infections, can cause short-term hyperthyroidism.

In rare situations, excess thyroid hormone can come from a source outside the thyroid, including struma ovarii, an abnormal tissue growth in the ovary that secretes thyroid hormone. Symptoms of hyperthyroidism also can be caused by taking thyroid supplements when they aren't needed.