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Last Updated: Mar 1, 2019


Hyperthyroidism occurs when the thyroid gland malfunctions and produces too much thyroid hormone. This condition is also known as overactive thyroid or thyrotoxicosis. An abnormal enlargement of the thyroid (goiter) develops in certain forms of hyperthyroidism.

thyroid gland

The thyroid gland is located in the anterior area of the neck and uses iodine atoms to produce two hormones, triiodothyronine (T3) and thyroxine (T4). T4 is produced and then converted to T3, the more active form of thyroid hormone. When these hormones are released in the blood, they affect numerous body functions, including metabolism, body temperature, body weight, heart rate, breathing, nervous system function, and muscle function. When a disorder makes the thyroid produce too much hormone, the body’s metabolism becomes abnormally accelerated.

Hyperthyroidism occurs in approximately 1% of the United States population. Most patients respond well to proper treatment although some experience potentially serious complications.

Causes and Risk Factors

Normally, an area of the brain called the hypothalamus signals the pituitary gland to produce thyroid-stimulating hormone (TSH) - a substance that regulates and maintains normal levels of thyroid hormones. When thyroid hormone levels are low, the pituitary releases TSH, which stimulates the thyroid to produce more T4. Conversely, when thyroid hormone levels are high, the pituitary decreases TSH and less T4 is produced. Certain diseases disrupt this system and cause the thyroid to produce excessive levels of T4 on its own. The most common causes of hyperthyroidism are Graves’ disease, toxic adenoma, toxic multinodular goiter, and thyroiditis.


hypothalamus and pituitary gland in brain cross section

The most common symptoms of hyperthyroidism include:


Complications that may arise as a consequence of hyperthyroidism include:


The symptoms of hyperthyroidism may resemble other disorders, making the disease difficult to diagnose on the basis of symptoms alone. Additionally, symptoms are often diminished or absent in elderly patients.

Patients with hyperthyroidism may display a tremor, overactive reflexes, eye changes, and warm, sweaty skin. An enlarged thyroid is not always present.

Blood tests detect high levels of thyroid hormones T3 and T4 and a low level of TSH. Other blood tests detect the specific anti-thyroid antibody present in patients with Graves’ disease. You can even order a home thyroid test online, which allows you to collect and mail a small sample of your blood for quick lab results (but remember to share these with your healthcare provider afterward).

An ultrasound creates images of the thyroid to check for abnormal growths. A thyroid radioiodine uptake test is a type of scan that helps determine the underlying cause of the disease.


There are no known methods to prevent naturally occurring forms of hyperthyroidism. However, patients who use thyroid medication should have their thyroid hormone levels checked at least once a year to avoid hyperthyroidism caused by taking too much medication.


Additional Resources

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Tina Shahian, PhD

Tina is a writer for Innerbody Research, where she has written a large body of informative guides about health conditions.


A communication specialist in life science and biotech subjects, Tina’s successful career is rooted in her ability to convey complex scientific topics to diverse audiences. Tina earned her PhD in Biochemistry from the University of California, San Francisco and her BS degree in Cell Biology from U.C. Davis. Tina Shahian’s Linkedin profile.


In her spare time, Tina enjoys drawing science-related cartoons.