Medically reviewed by Dr. C.H. Weaver M.D. updated 2/2021

The thyroid is a small gland that is located in the front of the neck below the larynx, or voice box. Along with the pituitary, adrenal, and other glands, the thyroid is part of the endocrine system, which produces, stores, and releases hormones into the blood stream to control various functions of the body’s cells. The production of thyroid hormones is regulated by thyroid-stimulating hormone (TSH), which is made by the pituitary gland. The thyroid hormones are known as triiodothyronine (T3) and thyroxine (T4).

What Is the Function of the Thyroid?

The thyroid produces hormones that regulate the body’s metabolism—the way the body uses energy. In addition to their effects on metabolism, thyroid hormones also affect brain development, breathing, heart and nervous system functions, body temperature, muscles strength, skin dryness, menstrual cycles, weight, and cholesterol levels.

Thyroid disorders may cause the thyroid to produce too much thyroid hormone (hyperthyroidism) or too little thyroid hormone (hypothyroidism) or to develop benign or cancerous nodules. Fortunately, recognition and treatment of these problems can improve both health and quality of life.

Hyperthyroidism

Hyperthyroidism is a disorder that occurs when the thyroid makes more thyroid hormone than the body needs. According to the National Institutes of Health (NIH), hyperthyroidism affects about 1 percent of the U.S. population and women are five to 10 times more likely to develop the disorder than men.

Factors that may increase chances of developing hyperthyroidism include a personal or family history of thyroid problems, certain medical conditions (pernicious anemia, type 1 diabetes, or adrenal insufficiency), a diet high in iodine, use of iodine-containing medications, age older than 60 years, and pregnancy or birth within the past six months.

Causes of hyperthyroidism include:

  • Graves disease—an autoimmune disease where an antibody causes overproduction of thyroid hormone
  • One or more thyroid nodules—lumps that can become overactive and produce too much thyroid hormone
  • Thyroiditis—inflammation of the thyroid gland, which causes stored thyroid hormone to leak and raise hormone levels in the blood
  • Ingesting too much iodine—through medications, including some used to treat heart conditions, and certain supplements
  • Overmedicating with synthetic thyroid hormone for treatment of underactive thyroid

Symptoms of hyperthyroidism include:

  • Nervousness or irritability
  • Fatigue or muscle weakness
  • Trouble sleeping
  • Heat intolerance
  • Hand tremors
  • Rapid and irregular heartbeat
  • Frequent bowel movements or diarrhea
  • Weight loss
  • Mood swings
  • Goiter (an enlarged thyroid that may cause your neck to look swollen)

Diagnosing Hyperthyroidism

To diagnose hyperthyroidism, a doctor will discuss a patient’s symptoms and perform a physical examination. If he or she finds reason to suspect hyperthyroidism, several tests may be used to confirm a diagnosis. Tests are also used to help determine the cause of the condition.

Tests for diagnosing hyperthyroidism include:

Thyroid-stimulating Hormone (TSH) Test - This test detects small amounts of TSH in the blood to measure thyroid activity. When there is too much thyroid hormone in the blood, the pituitary gland stops producing TSH. In general, a TSH level reading below normal indicates hyperthyroidism and a reading above normal indicates hypothyroidism.

T3 and T4 Test - If you have hyperthyroidism, this test will show that levels of T3 and/or T4 are higher than normal.

Radioactive Iodine Uptake Test - A measurement of the amount of iodine your thyroid collects from the bloodstream, this test will help show what is causing hyperthyroidism. Different levels of iodine uptake indicate different conditions.

Thyroid Scan -This scan shows how and where iodine is distributed in your thyroid to help diagnose the cause of hyperthyroidism.

Treating Hyperthyroidism

Doctors consider the cause of hyperthyroidism and how severe it is when choosing treatment. Other factors like a patient’s age, possible allergies to and side effects of medications, pregnancy, and heart disease are also considered. The goal of treatment of hyperthyroidism is to bring thyroid hormone levels to a normal range. Doing so is intended to prevent long-term complications and relieve symptoms.

Beta blockers may be prescribed to help control symptoms of hyperthyroidism until other medications begin working. Though beta blockers do not stop thyroid hormone production, they do block the effects of thyroid hormone on the body, which can help control symptoms like tremors, rapid heartbeat, and nervousness.

Antithyroid drugs, such as methimazole and propylthiouracil, block the way the thyroid gland uses iodine to make thyroid hormone. When antithyroid drugs are used, it may take several weeks or months before thyroid hormone levels reach a normal range. Potential side effects include allergic reactions (rashes and itching), a decreased white blood cell count (which lowers resistance to infection), and, rarely, liver failure. Pregnant women should not take methimazole and should be monitored if they are taking propylthiouracil. Both drugs should only be taken in small doses among women who are breastfeeding.

In radioiodine therapy, patients are administered iodine-131, which the thyroid gland collects in the same way that it regularly collects iodine in order to make thyroid hormone. The radioactive iodine, however, will gradually destroy the cells that make the thyroid gland; it will not affect other tissues in the body. Most patients who undergo radioiodine therapy will develop hypothyroidism; this, however, is considered an acceptable outcome, as hypothyroidism is easier to treat and has fewer long-term complications than hyperthyroidism. This treatment is not used in pregnant women or women who are breast feeding.

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Thyroid surgery is the least-used treatment for hyperthyroidism. It involves surgical removal of all or most of the thyroid gland. Removal of part of the thyroid may cause thyroid hormone levels to return to normal. Some patients, however, may develop hypothyroidism; these patients will need to take synthetic thyroid hormone, as will patients who have their entire thyroid removed (in this case, they will use thyroid hormone replacement for life). Thyroid surgery may be a treatment option for pregnant women who cannot tolerate antithyroid drugs, people with very large goiters, or people who have cancerous thyroid nodules. There are risks associated with thyroid surgery (damage to the parathyroid gland or laryngeal nerve, for example); more-experienced surgeons have a low rate of permanent complications.

Hypothyroidism

Hypothyroidism is a disorder where the thyroid gland doesn’t produce as much thyroid hormone as the body needs. According to the NIH, hypothyroidism affects about 5 percent of the U.S. population and women are more likely to develop it than men. The disease more commonly affects people over age 60.

Factors that may increase your chance of developing hypothyroidism include a personal or family history of thyroid disorders; another autoimmune disease (including Sjögren’s syndrome, pernicious anemia, type 1 diabetes, rheumatoid arthritis, or lupus); Turner syndrome (a genetic disorder that affects girls and women); or age older than 60 years. As well, women who have been pregnant or delivered a baby within the past six months and individuals who have received radiation to the thyroid or to the neck or chest may be at higher risk.

Causes of hypothyroidism include:

  • Hashimoto’s disease (also called chronic lymphocytic thyroiditis)—an autoimmune disorder where antibodies attack cells in the thyroid and interfere with their ability to make thyroid hormone
  • Thyroiditis—inflammation of the thyroid gland which causes stored thyroid hormone to leak and raise hormone levels in the blood
  • Congenital hypothyroidism—hypothyroidism that is present at birth
  • Surgical removal of part or all of the thyroid gland—may be performed for treatment of hyperthyroidism, a large goiter, thyroid nodules, or thyroid cancer
  • Radiation treatment of the thyroid—destruction of cells of the thyroid to treat hyperthyroidism; radiation to head and neck for conditions such as Hodgkin’s and other lymphomas and cancers of the head and neck can also damage the thyroid
  • Some medications

Symptoms of hypothyroidism include:

  • Fatigue
  • Weight gain
  • Puffy face
  • Cold intolerance
  • Joint and muscle pain
  • Constipation
  • Dry, thinning hair
  • Decreased sweating
  • Heavy or irregular menstrual periods and impaired fertility
  • Depression
  • Slowed heart rate

People with high cholesterol should also be tested for hypothyroidism, as this thyroid disorder can contribute to high blood cholesterol.

Diagnosing Hypothyroidism

To diagnose hypothyroidism, a doctor will likely discuss a patient’s symptoms and perform a physical examination. If he or she finds reason to suspect hypothyroidism, several tests may be used to confirm a diagnosis. Tests may also help determine the cause of the condition.

Tests for diagnosing hypothyroidism include:

Thyroid-stimulating Hormone (TSH) Test - This test detects small amounts of TSH in the blood to measure thyroid activity. When there is too much thyroid hormone in the blood, the pituitary gland stops producing TSH. In general, a TSH level reading below normal indicates hyperthyroidism and a reading above normal indicates hypothyroidism.

T4 Test - This test measures the amount of thyroid hormone circulating in the blood. In hypothyroidism, the level of T4 in the blood is below normal.

The Thyroid Autoantibody Test - The presence of thyroid autoantibodies suggests that Hashimoto’s disease is the cause of hypothyroidism (other causes are not associated with autoantibodies).

Treating Hypothyroidism

People with hypothyroidism are treated with synthetic thyroxine, a substance that is identical to the T4 made by the thyroid. Dosage will depend on the patient’s age and weight, severity of hypothyroidism, the presence of other health problems, and whether they are taking other medications that might interfere with how well the body uses thyroid hormone.

Pregnancy and Hypothyroidism

Uncontrolled hypothyroidism can increase the chance of certain complications among pregnant women. These include miscarriage, preterm delivery, and preeclampsia (a potentially serious complication that increases blood pressure). As well, untreated hypothyroidism can affect the baby’s growth and brain development. It’s important that pregnant women with hypothyroidism discuss the condition with their doctor—medications that are safe to take during pregnancy can help control hypothyroidism and prevent these complications.

Additional Reading on Thyroid Disease's

Key questions and considerations for patients By Julie Ann Sosa, MD, MA, FACS Professor of Surgery and Medicine, Duke University

Thyroid cancer happens when cells in the thyroid grow out of control. There are two main types of cells in the thyroid: follicular cells and C cells. Follicular cells use iodine from the blood that makes hormones which help regulate metabolism. C cells make calcitonin, a hormone that helps control how the body uses calcium. Less common cells in the thyroid are lymphocytes (immune system cells) and stromal cells.

Different cancers develop from each kind of cell, with each having a different level of disease and treatment. The three main types of malignant thyroid cancer are differentiated (including papillary, follicular, and Hṻrthle cell), medullary, and anaplastic (rare). In 2020, the ACS estimates ~ 65,000 individuals in the US will be diagnosed with thyroid cancer and 1,980 individuals will die from their cancer. Although the death rate has remained steady for thyroid cancer for many years, the chances of being diagnosed has tripled in the last 3 decades. This could be due to the use of thyroid ultrasound, which can detect small nodules.

Most thyroid cancers are found when a patient or a doctor feels a small or large lump in the neck. People with a family history of medullary thyroid cancer (MTC), with or without type 3 multiple endocrine neoplasia (MEN 2), might have a high risk for this type of cancer and may wish to undergo genetic testing.ncer in the CancerConnect private online thyroid cancer support group here.