Patient education: Hyperthyroidism (overactive thyroid) (Beyond the Basics)

HYPERTHYROIDISM OVERVIEW — Hyperthyroidism is the medical term for an overactive thyroid (the prefix "hyper" means excessive). In people with hyperthyroidism, the thyroid gland produces too much thyroid hormone. When this occurs, the body's metabolism is increased, which can cause a variety of symptoms.

This topic discusses the symptoms, diagnostic tests, and treatment options for hyperthyroidism. Hypothyroidism (a different condition in which the thyroid gland produces too little thyroid hormone) is discussed in a separate topic. (See "Patient education: Hypothyroidism (underactive thyroid) (Beyond the Basics)".)

WHAT IS THE THYROID? — The thyroid is a butterfly-shaped gland in the middle of the neck, located below the larynx (voice box) and above the clavicles (collarbones) (figure 1). The thyroid produces two hormones, triiodothyronine (T3) and thyroxine (T4), that regulate how the body uses and stores energy (also known as the body's metabolism).

The thyroid is controlled by a gland just below the brain, known as the pituitary. The pituitary produces thyroid-stimulating hormone (TSH), which in turn causes the thyroid gland to make T3 and T4. When the levels of T4 and T3 levels in the body are low, production of TSH increases in order to bring the levels up; when levels are high, TSH decreases.

HYPERTHYROIDISM CAUSES

Graves' disease — Graves' disease is the most common cause of hyperthyroidism. It is not clear why Graves' disease develops in most people, although it is more common in certain families.

In people with Graves' disease, the immune system produces an antibody that behaves like TSH in that it stimulates the thyroid gland to produce too much thyroid hormone. This is most common in women between the ages of 20 and 40 years but can occur at any age in men or women. The thyroid gland enlarges (called a goiter) (figure 2) and makes excessive amounts of thyroid hormone, causing symptoms of hyperthyroidism. (See 'Hyperthyroidism symptoms' below.)

Some people develop eye problems (called Graves' ophthalmopathy, orbitopathy, or simply thyroid eye disease); this causes dry, irritated, or red eyes and, in severe cases, may cause double vision. Other people develop swelling behind or around the eyes that causes the eyes to bulge out or inflammation of muscle in the eyelids that can cause excessive lid swelling or opening (figure 2). The more severe manifestations of Graves' eye disease are uncommon, except in people who smoke. In its most severe form, people with thyroid eye disease can develop inflammation of the optic nerves, which can result in loss of vision.

Other causes

●One or more thyroid nodules (small growths or lumps in the thyroid gland) can produce too much thyroid hormone. The nodule is then called a hot nodule, toxic nodule, or, when there is more than one, a toxic nodular goiter. (See "Patient education: Thyroid nodules (Beyond the Basics)".)

●Painless ("silent or lymphocytic") thyroiditis and postpartum thyroiditis are disorders in which the thyroid becomes temporarily inflamed and releases thyroid hormone stores into the bloodstream, causing hyperthyroidism.

Postpartum thyroiditis can occur several months after delivery. The hyperthyroid symptoms may last for several months, often followed by several months of hypothyroid symptoms, such as fatigue, muscle cramps, bloating, and weight gain.

●Subacute (granulomatous) thyroiditis is thought to be caused by a virus. It causes a painful, tender, enlarged thyroid gland. The thyroid becomes inflamed and releases thyroid hormone into the blood stream; the hyperthyroidism resolves when the viral infection improves and may also be followed by several months of hypothyroid symptoms. Coronavirus disease 2019 (COVID-19) has been associated with subacute thyroiditis.

●Taking too much thyroid hormone medication for hypothyroidism increases blood levels into the range seen in people with hyperthyroidism.

HYPERTHYROIDISM SYMPTOMS — Most people with hyperthyroidism have symptoms, including one or more of the following:

●Anxiety, irritability, trouble sleeping

●Weakness (in particular of the upper arms and thighs, making it difficult to lift heavy items or climb stairs or get up from a chair)

●Tremors (of the hands)

●Perspiring more than normal, difficulty tolerating hot weather

●Rapid, forceful, or irregular heartbeats

●Fatigue

●Weight loss in spite of a normal or increased appetite

●Frequent bowel movements

In addition, some women have irregular menstrual periods or stop having their periods altogether. This can be associated with infertility. Men may develop enlarged or tender breasts or erectile dysfunction, which resolves when hyperthyroidism is treated.

HYPERTHYROIDISM DIAGNOSIS — Hyperthyroidism can be diagnosed with blood tests that measure the amount of thyroid hormone and thyroid-stimulating hormone (TSH). Typically, the thyroid hormone level is high, and the TSH level is low. A thyroid scan or a blood test for the antibody that causes Graves' disease may also be recommended to help determine whether hyperthyroidism is caused by Graves' disease, toxic nodular goiter, or thyroiditis.

HYPERTHYROIDISM TREATMENT — Hyperthyroidism can be treated using medicine, radioiodine, or surgery. Many factors, such as your age and the severity and type of hyperthyroidism, as well as your preferences, are important in determining which treatment is best.

Medications — The two main types of medicines used to treat hyperthyroidism are antithyroid drugs and beta blockers.

Antithyroid drugs — Antithyroid drugs, such as methimazole (brand name: Tapazole) and propylthiouracil, work by decreasing how much thyroid hormone the body makes. Both are very effective, but methimazole is preferred because of a greater risk of serious side effects with propylthiouracil. Carbimazole is similar to methimazole and is used in many countries but not in the United States.

Because methimazole can be associated with serious birth defects if taken during pregnancy, propylthiouracil is the preferred drug during the first trimester; while propylthiouracil can also be associated with birth defects, they are less severe. For hyperthyroidism presenting after the first trimester, methimazole is preferred. (See "Patient education: Antithyroid drugs (Beyond the Basics)".)

If your health care provider prescribes an antithyroid drug, they will talk to you about how to take it and the possible side effects. (See "Patient education: Antithyroid drugs (Beyond the Basics)".)

Beta blockers — Beta blockers, such as atenolol or propranolol, are often started as soon as the diagnosis of hyperthyroidism is made. While beta blockers do not reduce thyroid hormone production, they can control many of the bothersome symptoms, such as rapid heart rate, tremors, anxiety, and heat intolerance. Once the hyperthyroidism is under control (with antithyroid drugs, surgery, or radioiodine), the beta blocker is stopped.

Radioiodine — Destroying the thyroid with radioiodine, called ablation, is a permanent way to treat hyperthyroidism. The amount of radiation used is small and does not cause cancer, infertility, or birth defects.

Radioiodine is given in liquid or capsule form, and it works by destroying much of the thyroid tissue. This takes approximately 6 to 18 weeks. People with severe symptoms, older adults, and people with heart problems should first be treated with an antithyroid drug to control symptoms. Most people who take radioiodine develop hypothyroidism and will need to take thyroid hormone supplements for the rest of their lives. (See "Patient education: Hypothyroidism (underactive thyroid) (Beyond the Basics)".)

As with most treatments, there are some risks with radioiodine:

●Sometimes, after apparently successful treatment, the condition returns, and further treatment is needed.

●Approximately 14 percent of people who use radioiodine treatment require a second dose. These people usually have severe hyperthyroidism or a very large goiter.

●Twice as many patients who receive radioiodine experience worsening of their eye disease compared with patients who have surgery.

People who are treated with radioiodine should avoid close physical contact, especially with young children and pregnant people, for five to seven days after treatment because of the possibility of exposing them to low doses of radiation. This can be difficult for parents of young children.

You will need to see your health care provider on a regular basis after treatment to have your thyroid hormone levels checked and monitor for hypothyroidism or recurrent hyperthyroidism.

Surgery — Although surgical removal of the thyroid is a permanent cure for hyperthyroidism, it is used far less often than antithyroid drugs because of the risks (and expense) associated with thyroid surgery. The risks include damage to the nerves to the voice box and damage to the parathyroid glands, which regulate the body's calcium balance.

However, surgery is recommended when:

●A large goiter blocks the airways, making it difficult to breathe

●You cannot tolerate antithyroid drugs and you do not want to use radioiodine

●There is a nodule in the thyroid gland that could be cancer

●You have active Graves' eye disease

●In people desiring pregnancy who want definitive treatment before conceiving

The follow-up after surgery includes regular appointments to test your thyroid hormone levels and monitor for signs of hypo- and hyperthyroidism. Almost everyone develops hypothyroidism after surgery and requires treatment with thyroid hormone. (See "Patient education: Hypothyroidism (underactive thyroid) (Beyond the Basics)".)

PREGNANCY AND HYPERTHYROIDISM — If you take antithyroid drugs and are considering future pregnancy, you should discuss your treatment with your health care provider before trying to get pregnant. There are risks to the mother and developing baby if hyperthyroidism is not well controlled; these risks can be avoided or minimized with frequent monitoring and medication adjustment throughout the pregnancy.

People who are pregnant or breastfeeding should not be treated with radioiodine. Having radioiodine treatment or surgery before becoming pregnant usually eliminates the need for antithyroid drugs and any possible associated risks. A person should wait at least six months after radioiodine treatment before trying to become pregnant.

WHERE TO GET MORE INFORMATION — Your health care provider is the best source of information for questions and concerns related to your medical problem.

This article will be updated as needed on our website (www.uptodate.com/patients). Related topics for patients, as well as selected articles written for health care professionals, are also available. Some of the most relevant are listed below.

Patient level information — UpToDate offers two types of patient education materials.

The Basics — The Basics patient education pieces answer the four or five key questions a patient might have about a given condition. These articles are best for patients who want a general overview and who prefer short, easy-to-read materials.

Patient education: Hyperthyroidism (overactive thyroid) (The Basics)
Patient education: Thyroid nodules (The Basics)
Patient education: Congenital hypothyroidism (The Basics)
Patient education: Nodular goiter (The Basics)
Patient education: Pituitary adenoma (The Basics)
Patient education: Periodic paralysis syndrome (The Basics)
Patient education: Thyroiditis after pregnancy (The Basics)
Patient education: Hyperthyroidism (overactive thyroid) and pregnancy (The Basics)
Patient education: Thyroiditis (The Basics)

Beyond the Basics — Beyond the Basics patient education pieces are longer, more sophisticated, and more detailed. These articles are best for patients who want in-depth information and are comfortable with some medical jargon.

Patient education: Hypothyroidism (underactive thyroid) (Beyond the Basics)
Patient education: Thyroid nodules (Beyond the Basics)
Patient education: Antithyroid drugs (Beyond the Basics)

Professional level information — Professional level articles are designed to keep doctors and other health professionals up-to-date on the latest medical findings. These articles are thorough, long, and complex, and they contain multiple references to the research on which they are based. Professional level articles are best for people who are comfortable with a lot of medical terminology and who want to read the same materials their doctors are reading.

Amiodarone and thyroid dysfunction
Beta blockers in the treatment of hyperthyroidism
Bone disease with hyperthyroidism and thyroid hormone therapy
Cardiovascular effects of hyperthyroidism
Hyperthyroidism during pregnancy: Clinical manifestations, diagnosis, and causes
Clinical manifestations and diagnosis of Graves disease in children and adolescents
Hyperthyroidism during pregnancy: Treatment
Diagnosis of hyperthyroidism
Disorders that cause hyperthyroidism
Evaluation and management of neonatal Graves disease
Exogenous hyperthyroidism
Iodinated radiocontrast agents in the treatment of hyperthyroidism
Iodine in the treatment of hyperthyroidism
Neurologic manifestations of hyperthyroidism and Graves' disease
Overview of the clinical manifestations of hyperthyroidism in adults
Radioiodine in the treatment of hyperthyroidism
Subclinical hyperthyroidism in nonpregnant adults
Surgical management of hyperthyroidism
Thionamides in the treatment of Graves' disease
Graves' hyperthyroidism in nonpregnant adults: Overview of treatment

The following organizations also provide reliable health information.

●National Library of Medicine

(www.nlm.nih.gov/medlineplus/healthtopics.html)

●The American Thyroid Association

(www.thyroid.org)

●Thyroid Foundation of Canada

(www.thyroid.ca)

●Hormone Health Network

(www.hormone.org, available in English and Spanish)

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