Hyperthyroidism is a condition in which the thyroid gland is overactive, and makes too much thyroid hormone (called thyroxine [T4 ] and triiodothyronine [T3 ]). Hormones are substances that affect and control many important functions in the body.

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

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
• Inflammation (irritation and swelling) of the thyroid due to viral infections or other causes
• Non-cancerous growths of the thyroid gland or pituitary gland
• Taking large amounts of thyroid hormone
• Tumors of the testes or ovaries

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

Related topics:

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

• Difficulty concentrating
• Fatigue
• Frequent bowel movements
• Goiter (visibly enlarged thyroid gland) or thyroid nodules
• Heat intolerance
• Increased appetite
• Increased sweating
• Irregular menstrual periods in women
• Nervousness
• Restlessness
• Weight loss (rarely, weight gain)

Other symptoms that can occur with this disease:

• Bounding pulse
• Breast development in men
• Clammy skin
• Diarrhea
• Hair loss
• Hand tremor
• Weakness
• High blood pressure
• Itching - overall
• Lack of menstrual periods in women
• Nausea and vomiting
• Protruding eyes (exophthalmos)
• Rapid, forceful, or irregular heartbeat (palpitations)
• Skin blushing or flushing
• Sleeping difficulty

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

Laboratory tests that evaluate thyroid function:

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

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

• Cholesterol test
• Glucose test
• Radioactive iodine uptake
• T3RU
• Triglycerides
• Vitamin B-12

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

• 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 radiation or surgery, 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.

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.

Treatments for hypothyroidism, such as radioactive iodine, surgery, and medications to replace thyroid hormones can have complications.

• Heart-related complications include rapid heart rate, congestive heart failure, and atrial fibrillation.
• Thyroid crisis or storm is an acute worsening of hyperthyroidism symptoms that may occur with infection or stress. Fever, decreased mental alertness, and abdominal pain may occur. Immediate hospitalization is needed.
• Hyperthyroidism increases the risk for osteoporosis.
• There may be complications related to surgery. These include scarring of the neck, hoarseness from nerve damage to the voice box, and a low calcium level from damage to the parathyroid glands (located near the thyroid gland).
• Complications may be due to thyroid hormone replacement. If too little hormone is given, symptoms of underactive thyroid can occur. These include fatigue, increased cholesterol levels, weight gain, depression, and slowing of mental and physical activity. If too much hormone is given, the symptoms of hyperthyroidism will come back.

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

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: Koronenberg HM, Shlomo M, Polonsky KS, Larsen PR, eds. Williams Textbook of Endocrinology. 11th ed. Philadelphia, Pa: Saunders Elsevier; 2008:chap 11.