Endocrine System Home > Hyperthyroidism Causes

In the United States, Graves' disease is the most common cause of hyperthyroidism. However, there are a number of other reasons why a person might develop an overactive thyroid. Some of these -- such as thyroiditis or thyroid nodules -- occur within the thyroid gland, while others -- such as taking too much synthetic thyroid hormone -- occur in other places within the body.

What Causes Hyperthyroidism?

A number of different conditions can cause hyperthyroidism. Some of these can occur within the thyroid gland itself, including:
Other hyperthyroidism causes can be found outside the thyroid gland. They include:
  • Consuming too much iodine (iodine-induced hyperthyroidism)
  • Taking too much synthetic thyroid hormone
  • A pituitary adenoma.

Causes of Hyperthyroidism Within the Thyroid

Several possible causes of an overactive thyroid that occur within the thyroid gland itself are explained in the following sections.
Graves' Disease
Graves' disease is the most common cause of hyperthyroidism in the United States. This is a type of autoimmune disease, which means the body's immune system attacks its own healthy cells and tissues for some unknown reason.
In Graves' disease, the immune system makes an antibody called thyroid-stimulating immunoglobulin (TSI), which mimics thyroid-stimulating hormone (TSH) and causes the thyroid to make more thyroid hormone than the body needs.
Graves' disease affects 2 percent of all women at some point in their lives. It tends to affect women between the ages of 20 and 40, although it does occur in infants, children, and the elderly of both sexes.
Graves' disease is also known as toxic diffuse goiter.
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Last reviewed by: Arthur Schoenstadt, MD
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