Hyperthyroidism occurs when the body has too much thyroid hormone which can be caused by an overactive thyroid that makes too much thyroid hormone or by release of thyroid hormone as the gland is destroyed.

An overactive thyroid is the most common cause of hyperthyroidism and can be caused by Graves' disease (also known as diffuse toxic goiter or when the whole thyroid is hyperactive), toxic multinodular goiter (when more than one nodule is hyperactive), or a toxic nodule (when just one nodule is hyperactive). Approximately 1 million patients in the United States have Graves' disease, the most common cause of hyperthyroidism. Other rare causes of hyperthyroidism include certain medications such as amiodarone (used for certain irregular heart rhythms), eating too much iodine, and rare diseases of the ovary or testicles that can cause the thyroid to be over-stimulated. 

Signs and Symptoms

Symptoms associated with hyperthyroidism include:

  • Nervousness and irritability
  • Increased resting heart rate
  • Heat intolerance and increased sweating
  • Tremor
  • Weight loss or alterations in appetite
  • Frequent bowel movements
  • Sudden paralysis
  • Thyroid enlargement (lump in the neck)
  • Thick redness on the front of legs (pretibial myxedema), which occurs with Graves' Disease
  • Thin, delicate skin and irregular fingernail and hair growth
  • Menstrual disturbance (decreased flow)
  • Impaired fertility
  • Mental disturbances
  • Sleep disturbances (including insomnia)

It is very important to keep in mind that the symptoms of hyperthyroidism are non-specific and can be found with a number of other diseases. While these symptoms MAY be found in patients with hyperthyroidism, the symptoms do not make the diagnosis. The diagnosis of hyperthyroidism is made with blood tests and careful evaluation by an experienced physician.


A patient's history and physical exam are important factors in making the diagnosis of hyperthyroidism. Some patients may have tachycardia (i.e. a rapid heart rate), arrhythmias (i.e. an irregular heart rate such as atrial fibrillation), tremors, thyroid bruit (i.e. a rushing sound in the thyroid when listened to with a stethoscope), a larger than normal thyroid, and eye abnormalities (dryness, bulging eyes, double vision). Blood tests are critical to confirming the diagnosis. Patients with hyperthyroidism will usually have a low TSH and a higher than normal T4 and/or T3 level. In fact, some patients may have no symptoms at all, but blood tests that make the diagnosis of hyperthyroidism.


Once the diagnosis is made, patients will have a RAI scan (i.e. radioactive iodine scan). In this test, patients are given a small dose of radioactive iodine that homes into the thyroid and reveals which areas of the thyroid are hyperactive or "hot." The RAI scan will determine if the hyperthyroidism is caused by an overactive thyroid (i.e. the thyroid will be hotter than normal) or destruction from thyroiditis (i.e. the thyroid will be colder than normal). If the thyroid is overactive, the RAI scan will determine if the whole gland is hyperactive as in Graves' disease or just certain areas as in toxic multinodular goiter, or if just one area is hyperactive as in a toxic nodule.


Hyperthyroidism may be treated with

  1. medications (anti-thyroid medications),
  2. radioactive iodine ablation (RAI ablation),
  3. removal of the thyroid gland (hemithyroidectomy or total thyroidectomy).

Ultimately, the choice of treatment depends on the cause of hyperthyroidism as well as a number of patient-related factors. Thyroiditis often does not require specific treatment because this type of hyperthyroidism usually gets better on its own within a few months. Patients with a toxic adenoma will either receive RAI ablation or removal of the half of the thyroid with the hyperactive thyroid. For patients with Graves' disease or toxic multinodular goiters, treatment usually starts with anti-thyroid medications such as Methimazole or Propylthiouracil (PTU). These medications are designed to stop the production and release of thyroid hormone. In some cases, patients may receive a medication that is designed to block the effect of thyroid hormone on the body such as a beta-blocker. However, only 30% of patients have long-term control of hyperthyroidism with medical therapy. Most patients go on to have a more definitive therapy such as RAI ablation or surgery. See RAI Ablation » | See Thyroid Surgery ».

Both treatments have equal success rates and complication rates. In the United States, many patients will have RAI ablation, however clear reasons to have a total thyroidectomy include: a large goiter, nodules that present a risk of thyroid cancer, pregnant patients, a desire to become pregnant within a year of treatment, ocular Graves' disease (i.e. the patient has eye symptoms caused by Graves' disease), a need to control the hyperthyroidism quickly (RAI ablation usually takes 3 to 6 months to work), iodine allergy, children younger than 15, and patient preference. The decision between which therapy is right for the patient should be made with an experienced thyroid specialist who can take into account all the different factors. Regardless of whether the patient has RAI ablation or surgery, the goal of both treatments is to make the patient hypothyroid (i.e. not make enough thyroid hormone). Low dose RAI ablation and partial thyroidectomy is no longer recommended because the chance of hyperthyroidism coming back (i.e. recurring) is high. Patients will require thyroid hormone replacement after appropriate definitive therapy. See RAI Scan ».