In hyperthyroidism, the thyroid gland overproduces thyroid hormones. These hormones regulate the body’s metabolism (the chemical reactions that keep the body functioning), and excessive amounts cause body processes to speed up.
Hyperthyroidism is most commonly caused by Graves’ disease, an autoimmune disorder in which the immune system attacks the thyroid, stimulating it to produce more hormones. Other causes include benign tumors called thyroid nodules and the side effects of certain medications.
Symptoms tend to develop slowly and include weight loss, rapid heartbeat, restlessness, anxiety, insomnia, twitching or trembling, increased sweating, and, in severe cases, enlargement of the thyroid (goiter).
In Graves’ disease, the eyes may also bulge out. Untreated, hyperthyroidism may lead to complications such as heart problems and osteoporosis (thinning of the bones).
Treatment may be with medication, radioactive iodine to destroy excess thyroid tissue, or surgery to remove part of the thyroid gland.