What is hyperthyroidism?

Hyperthyroidism is a disorder that develops when the thyroid, a butterfly-shaped gland in the front of the neck, makes more thyroid hormone than the body requires. The disease can also lead to the hypermetabolic condition known as thyrotoxicosis, which is used to describe the presence of too much thyroid hormone in the blood. Because thyroid hormones circulate through the body in the bloodstream, they affect almost every tissue and cell in the body. The disease speeds up many of the body’s functions.

What are the symptoms of hyperthyroidism?

Although signs of hyperthyroidism vary among individuals, some common symptoms of the disease include the following:

  • Nervousness or irritability
  • Fatigue or muscle weakness
  • Inability to tolerate heat
  • Difficulty sleeping
  • Rapid and irregular heartbeat
  • Hand tremors
  • Frequent bowel movements or diarrhea
  • Weight loss
  • Mood swings
  • An enlarged thyroid, called a goiter, that can produce swelling in the neck, which may interfere with normal breathing and swallowing

What causes hyperthyroidism?

Hyperthyroidism is most commonly caused by Graves’ disease, an autoimmune disorder that’s also known as toxic diffuse goiter. Graves’ disease develops when the immune system makes a substance called thyroid stimulating immunoglobin, or TSI, that latches onto thyroid cells and causes this gland to make too much thyroid hormone.

In addition, lumps called thyroid nodules, or adenomas, also cause hyperthyroidism when they become overactive and produce too much thyroid hormone. Thyroiditis, an inflammation of the thyroid gland, is another trigger for hyperthyroidism that causes stored supplies of thyroid hormone to seep into the blood, temporarily raising levels of this substance in the bloodstream.

Hyperthyroidism can also develop when people consume too much iodine in food, medications or in supplements containing seaweed. Excessive amounts of iodine can cause the thyroid to make too much thyroid hormone and trigger the disease.

In addition, people who take synthetic thyroid hormone to treat hypothyroidism, a condition that occurs when thyroid hormone levels are too low, may take too much of the drug and develop hyperthyroidism.

Who is at risk for hyperthyroidism? 

  • Women are 2 to 10 times more likely than men to develop hyperthyroidism. 
  • People who have a family history of thyroid disease.
  • If you have other health problems, such as type 1 diabetes, the hormonal disorder primary adrenal insufficiency and pernicious anemia, a condition caused by a vitamin B12 deficiency.
  • If you’re older than the age of 60. 
  • Those who eat large amounts of food containing iodine, such as kelp, or use medicines that contain iodine, such as amiodarone, a heart medicine.
  • Women who were pregnant within the past 6 months.

How is hyperthyroidism diagnosed?

In general, when doctors suspect hyperthyroidism, to confirm the disease, they take a patient’s medical history and conduct a thorough physical exam. In addition, doctors would order blood tests to check for the presence of specific hormones, antibodies and levels of iodine in the bloodstream, as well as how and where in the thyroid iodine is being distributed.

How is hyperthyroidism treated?

The first step in treating hyperthyroidism is finding the right specialist to administer therapy. The goal of treatment for hyperthyroidism involves bringing thyroid hormone to normal levels using medications, radioiodine therapy or thyroid surgery. But because no single treatment works for everyone, doctors consider a number of variables, such as the age of a patient, allergic reactions to or side effects of the meds, and the presence of other conditions or illnesses. In addition, treatment also depends on the cause and severity of a patient’s hyperthyroidism.

Medications most commonly used for treating hyperthyroidism include beta-blockers to reduce symptoms of the diseases and antithyroid drugs, such as methimazole (Tapazole, Northyx), to adjust the levels of thyroid hormones.

Radioiodine therapy is another effective way doctors treat the disease. Patients take an oral dose of radioactive iodine-131 that affects only the thyroid gland. The radioactive iodine destroys part of the thyroid gland so the remaining part of the thyroid functions normally.

Surgery is the least common treatment for hyperthyroidism. But when surgeons choose to operate, they remove part or most of the thyroid gland to bring thyroid hormone levels back to normal. If for any reason, doctors completely remove the thyroid gland, then patients are placed on lifelong hormone medication so the body can function normally.

Last Reviewed: February 25, 2019