Hyperthyroidism, the result of an overactive thyroid, more commonly affects women between the ages of 20 and 40, but men can also develop this condition. The symptoms of this thyroid condition can be frightening.

Symptoms can include

  • Muscle weakness
  • Trembling hands
  • Rapid heartbeat
  • Fatigue
  • Weight loss
  • Diarrhea or frequent bowel movements
  • Irritability and anxiety
  • Vision problems (irritated eyes or difficulty seeing)
  • Menstrual irregularities
  • Intolerance to heat and increased sweating
  • Infertility

Causes of Hyperthyroidism

Graves' disease is the most common cause of hyperthyroidism. It occurs when the immune system produces antibodies that attack the thyroid gland, making it produce too much thyroid hormone. This condition happens often in people with a family history of thyroid disease. In some people with Graves' disease, one of the noticeable symptoms may be swelling behind the eyes, causing discomfort or increased tearing, or causing the eyes to bulge.

Other causes of hyperthyroidism include the following:

  • Thyroid nodules.
  • Taking too much thyroid hormone medication to treat other conditions.
  • Subacute thyroiditis. This painful inflammation of the thyroid is usually caused by a virus. When the infection leaves, the condition improves.
  • Lymphocytic thyroiditis and postpartum thyroiditis. These related autoimmune disorders cause a temporary painless inflammation of the gland. Thyroiditis leads to leakage of thyroid hormone from the inflamed gland, raising hormone levels in the bloodstream.


Antithyroid Drugs: These drugs decrease the amount of hormone the thyroid gland makes. For most people, the preferred drug is methimazole (tapazole) because of its safety record. Another drug, propylthiouracil (PTU), may be preferred for people who are allergic to or intolerant of methimazole and for pregnant women in their first trimester of pregnancy.

Antithyroid drugs may have to be taken for an extended period—even one to two years or longer. The thyroid condition may go away, but there could be a relapse, (return of hyperthyroidism). Therapy with antithyroid drugs is typically thought of as either short term or long term. Short-term therapy is used to make the thyroid blood tests normal before a decision is reached about a more permanent treatment. Long-term therapy is sometimes used to try to make the disease go into remission even after the antithyroid drug is stopped.

Beta-blockers: Beta-blocker drugs, such as atenolol or propranolol, do not block the production of thyroid hormone. Instead, they control many troubling symptoms of hyperthyroidism, especially rapid heart rate, trembling, anxiety, and the high amount of heat the body produces.

Radioactive iodine: The thyroid gland normally collects iodine out of the bloodstream to make thyroid hormone. Radioactive iodine treatment involves taking a radioactive form of iodine that causes the permanent destruction of the thyroid. The response to treatment can take from 6 to 18 weeks. Because the radioiodine often destroys some of the normal function of the thyroid gland, people who have this therapy will likely need to take thyroid hormone for the rest of their lives to replace their hormone levels.

Surgery: Removal of the thyroid gland (thyroidectomy) is another permanent solution, but is often the least preferred option. This procedure must be performed by a highly skilled and experienced thyroid surgeon because of the risk of damage to nerves around the larynx (voice box) and to the nearby parathyroid glands, which control calcium metabolism in the body. Surgery is recommended when there is a large goiter (enlarged thyroid gland) that makes breathing difficult or when antithyroid drugs are not working, or when there are reasons not to take radioactive iodine. It may also be used in people who also have thyroid nodules, especially when the nodules may be cancerous.  

After both radioactive iodine and surgery treatments, the patient will need to be monitored regularly for adequate thyroid hormone levels in the blood. After surgery, most people no longer produce enough thyroid hormone, so they must take a daily supplement of synthetic thyroid hormone.

If left untreated, hyperthyroidism can lead to other health problems including congestive heart failure, abnormal heartbeat, and loss of bone mineral (osteoporosis).


Leonard Wartofsky, MD, MACP
Washington Hospital Center
Georgetown University School of Medicine

Bryan Haugen, MD
University of Colorado Denver School of Medicine

Last Review: May 2013