Alternative names
Thyrotoxicosis; Overactive thyroid

Hyperthyroidism is an imbalance of metabolism caused by overproduction of thyroid hormone.

Causes, incidence, and risk factors

The thyroid gland is located in the neck. It produces several hormones which control the way that every cell in the body uses energy (metabolism). The thyroid is part of the endocrine system.

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

  • Graves’ disease  
  • Non-cancerous growths of the thyroid gland or pituitary gland  
  • Tumors of the testes or ovaries  
  • Inflammation (irritation and swelling) of the thyroid due to viral infections or other causes  
  • Ingestion of excessive amounts of thyroid hormone  
  • Ingestion of excessive iodine

Graves’ disease accounts for 85% of all cases of hyperthyroidism.

Related topics:

  • Painless (silent) thyroiditis  
  • Factitious hyperthyroidism  
  • Hypothyroidism  
  • Graves’ disease


  • Weight loss  
  • Increased appetite  
  • Nervousness  
  • Restlessness  
  • Heat intolerance  
  • Increased sweating  
  • Fatigue  
  • Frequent bowel movements  
  • Menstrual irregularities in women  
  • Goiter (visibly enlarged thyroid) may be present

Additional symptoms that may be associated with this disease:

  • Weakness  
  • Sleeping difficulty  
  • Clammy skin  
  • Skin blushing or flushing  
  • Bounding pulse  
  • Nausea and vomiting  
  • Lack of menstruation  
  • Itching - overall  
  • Heartbeat sensations  
  • Hand tremor  
  • Hair loss  
  • Diarrhea  
  • Breast development in men  
  • High blood pressure  
  • Protruding eyes (exophthalmos)

Signs and tests
Vital signs (temperature, pulse, rate of breathing, blood pressure) show increased heart rate. Systolic blood pressure may be elevated. Physical examination may reveal thyroid enlargement or goiter.

Laboratory tests that evaluate thyroid function:

  • Serum TSH is usually decreased  
  • T3 and free T4 are usually elevated

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

  • Vitamin B-12  
  • TSI  
  • Triglycerides  
  • RT3U  
  • Radioactive iodine uptake  
  • Glucose test  
  • Cholesterol test  
  • Antithyroglobulin antibody


Treatment varies depending on the cause of the condition and the severity of symptoms. Hyperthyroidism is usually treated with antithyroid medications, radioactive iodine (which destroys the thyroid and thus stops the excess production of hormones), or surgery to remove the thyroid.

If the thyroid must be removed with radiation or surgery, replacement thyroid hormones must be taken for the rest of the person’s life.

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

Expectations (prognosis)

Hyperthyroidism caused by Graves’ disease is usually progressive and has many associated complications, some of which are severe and affect quality of life.

These include complications caused by use of radioactive iodine, surgery, and medications to replace thyroid hormones. However, hyperthyroidism is generally treatable and rarely fatal.


  • Cardiac complications include rapid heart rate, congestive heart failure, and Atrial Fibrillation.  
  • Thyroid crisis or “storm” is an acute worsening of the symptoms of hyperthyroidism that may occur with infection or stress. Fever, decreased mental alertness, and abdominal pain may occur, and immediate hospitalization is indicated.  
  • Hyperthyroidism increases the risk for osteoporosis.  
  • There may be complications related to surgery, including visible scarring of the neck, hoarseness due to nerve damage to the voicebox, and a low calcium level because of damage to the parathyroid glands.  
  • Complications may be related to replacement of thyroid hormones. If too little hormone is given, symptoms of under-active thyroid can occur including fatigue, increased cholesterol levels, mild weight gain, depression, and slowing of mental and physical activity.

Calling your health care provider

Call your health care provider if you have symptoms which could be caused by excessive thyroid hormone production. If the symptoms are associated with a rapid, irregular heartbeat, dizziness, or change in consciousness, go to the emergency room or call the local emergency number (such as 911).

Call your health care provider if treatment for hyperthroidism induces symptoms of under-active thyroid, including mental and physical sluggishness, weight gain, and depression.

There are no general prevention measures to prevent hyperthyroidism.

Johns Hopkins patient information

Last revised: December 4, 2012
by Amalia K. Gagarina, M.S., R.D.

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