Printer Friendly VersionEmail A FriendAdd ThisIncrease Text SizeDecrease Text Size




Hyperthyroidism is a condition in which the thyroid gland makes too much thyroid hormone. The condition is often referred to as an "overactive thyroid."

Alternative Names

Overactive thyroid


The thyroid gland is an important organ of the endocrine system. It is located in the front of the neck just below the voice box. The gland produces the hormones thyroxine (T4) and triiodothyronine (T3), which control the way every cell in the body uses energy. This process is called yourmetabolism.

Hyperthyroidism occurs when the thyroid releases too much of its hormones over a short (acute) or long (chronic) period of time. Many diseases and conditions can cause this problem, including:

  • Getting too much iodine
  • Graves disease (accounts for most cases of hyperthyroidism)
  • Inflammation (thyroiditis) of the thyroid due to viral infections or other causes
  • Noncancerous growths of the thyroid gland or pituitary gland
  • Taking large amounts of thyroid hormone
  • Tumors of the testes or ovaries

Related topics:


Other symptoms that can occur with this disease:

Signs and tests

Physical examination may reveal thyroid enlargement, tremor, hyperactive reflexes, or an increased heart rate. Systolic blood pressure (the first number in a blood pressure reading) may be high.

Subclinical hyperthyroidism is a mild form of hyperthyroidism that is diagnosed by abnormal blood levels of thyroid hormones, often in the absence of any symptoms.

Blood tests are also done to measure levels of thyroid hormones.

  • TSH (thyroid stimulating hormone) level is usually low
  • T3 and free T4 levels are usually high

This disease may also affect the results of the following tests:

Support Groups

Expectations (prognosis)

Hyperthyroidism is generally treatable and only rarely is life threatening. Some of its causes may go away without treatment.

Hyperthyroidism caused by Graves disease usually gets worse over time. It has many complications, some of which are severe and affect quality of life.

Calling your health care provider

Call your health care provider if you have symptoms that could be caused by too much thyroid hormone production. Go to an emergency room or call the local emergency number (such as 911), if you have:

  • Change in consciousness
  • Dizziness
  • Rapid, irregular heartbeat

Call your health care provider if you are being treated for hyperthyroidism and you develop symptoms of underactive thyroid, including:

  • Depression
  • Mental and physical sluggishness
  • Weight gain

Thyroid crisis (storm), also called thyrotoxicosis, is a sudden worsening of hyperthyroidism symptoms that may occur with infection or stress. Fever, decreased mental alertness, and abdominal pain may occur. Immediate hospitalization is needed.

Other complications related to hyperthyroidism include:

  • Heart-related complications including:
  • Increased risk for osteoporosis, if hyperthyroidism is present for a long time
  • Surgery-related complications, including:
    • Scarring of the neck
    • Hoarseness due to nerve damage to the voice box
    • Low calcium level due to damage to the parathyroid glands (located near the thyroid gland)
  • Treatments for hypothyroidism, such as radioactive iodine, surgery, and medications to replace thyroid hormones can have complications.


How the condition is treated depends on the cause and the severity of symptoms. Hyperthyroidism is usually treated with one or more of the following:

  • Antithyroid medications
  • Radioactive iodine (which destroys the thyroid and stops the excess production of hormones)
  • Surgery to remove the thyroid

If the thyroid must be removed with surgery or destroyed with radiation, you must take thyroid hormone replacement pills for the rest of your life.

Beta-blockers such as propranolol are used to treat some of the symptoms, including rapid heart rate, sweating, and anxiety until the hyperthyroidism can be controlled.


There are no known ways to prevent hyperthyroidism.


AACE Thyroid Task Force. American Association of Clinical Endocrinologists medical guidelines for clinical practice for the evaluation and treatment of hyperthyroidism and hypothyroidism. Endocr Pract. 2002;8(6).

Davies TF, Larsen PR. Thyrotoxicosis. In: Kronenberg HM, Melmed S, Polonsky KS, Larsen PR, eds. Williams Textbook of Endocrinology. 11th ed. Philadelphia, Pa: Saunders Elsevier; 2008:chap 11.

Ladenson P, Kim M. Thyroid. In: Goldman L, Ausiello D, eds. Cecil Medicine. 23rd ed. Philadelphia, Pa: Saunders Elsevier; 2007:chap 244.

Review Date: 4/19/2010
Reviewed By: Ari S. Eckman, MD, Division of Endocrinology and Metabolism, Johns Hopkins School of Medicine, Baltimore, MD. Review provided by VeriMed Healthcare Network. Also reviewed by David Zieve, MD, MHA, Medical Director, A.D.A.M., Inc.
A.D.A.M., Inc. is accredited by URAC, also known as the American Accreditation HealthCare Commission ( URAC's accreditation program is an independent audit to verify that A.D.A.M. follows rigorous standards of quality and accountability. A.D.A.M. is among the first to achieve this important distinction for online health information and services. Learn more about A.D.A.M.'s editorial policy, editorial process and privacy policy. A.D.A.M. is also a founding member of Hi-Ethics and subscribes to the principles of the Health on the Net Foundation (
The information provided herein should not be used during any medical emergency or for the diagnosis or treatment of any medical condition. A licensed medical professional should be consulted for diagnosis and treatment of any and all medical conditions. Call 911 for all medical emergencies. Links to other sites are provided for information only -- they do not constitute endorsements of those other sites. © 1997- 2009 A.D.A.M., Inc. Any duplication or distribution of the information contained herein is strictly prohibited.

Home Page
Why Choose Us
Website Terms of Use

Visitor & Patient Info
Patient Portal
We Speak Your Language
Patient Privacy
Contact Us

Find a Physician
Medical Services
Maimonides In the News
Directions & Parking

Medical Education
Career Opportunities
Nurses & Physicians
Staff Intranet Access
Maimonides Medical Center    |    4802 Tenth Avenue    |    Brooklyn, NY 11219    |    718.283.6000    |