Hyperthyroidism is a condition caused by an overactive thyroid gland. The gland makes too much T4 and T3 hormones. 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 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 (taking in through the mouth, such as in eating) of large 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

• 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)

Physical examination may reveal thyroid enlargement or goiter. Vital signs (temperature, pulse, rate of breathing, blood pressure) show 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 is usually low
• T3 and free T4 are usually high

• 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 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.

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 treatment such as use of radioactive iodine, surgery, and medications to replace thyroid hormones. However, hyperthyroidism is generally treatable and rarely fatal.

• Heart-related 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 needed.
• 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 voice box, 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. If too much hormone is given, the symptoms of hyperthyroidism will come back.

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 hyperthyroidism induces symptoms of under-active thyroid, including mental and physical sluggishness, weight gain, and depression.

There are no general prevention measures 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).