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Hypothyroidism (Underactive Thyroid)

What is hypothyroidism?

Hypothyroidism, also called underactive thyroid, is when the thyroid gland doesn’t make enough thyroid hormones to meet your body’s needs. The thyroid is a small, butterfly-shaped gland in the front of your neck. Thyroid hormones control the way the body uses energy, so they affect nearly every organ in your body, even the way your heart beats. Without enough thyroid hormones, many of your body’s functions slow down.

Illustration of the thyroid and its location in the neck.
The thyroid is a small gland in your neck that makes thyroid

How common is hypothyroidism?

About 4.6 percent of the U.S. population ages 12 and older has hypothyroidism, although most cases are mild.1 That’s almost 5 people out of 100.

Who is more likely to develop hypothyroidism?

Women are much more likely than men to develop hypothyroidism. The disease is also more common among people older than age 60.1

You are more likely to have hypothyroidism if you

Is hypothyroidism during pregnancy a problem?

Hypothyroidism that isn’t treated can affect both the mother and the baby. However, thyroid medicines can help prevent problems and are safe to take during pregnancy. Learn more about causes, diagnosis, and treatment of hypothyroidism during pregnancy.

What other health problems could I have because of hypothyroidism?

Hypothyroidism can contribute to high cholesterol, so people with high cholesterol should be tested for hypothyroidism. Rarely, severe, untreated hypothyroidism may lead to myxedema coma, an extreme form of hypothyroidism in which the body’s functions slow to the point that it becomes life threatening. Myxedema coma requires immediate medical treatment.

What are the symptoms of hypothyroidism?

Hypothyroidism has many symptoms that can vary from person to person. Some common symptoms of hypothyroidism include

  • fatigue
  • weight gain
  • a puffy face
  • trouble tolerating cold
  • joint and muscle pain
  • constipation
  • dry skin
  • dry, thinning hair
  • decreased sweating
  • heavy or irregular menstrual periods
  • fertility problems
  • depression
  • slowed heart rate
  • goiter

Because hypothyroidism develops slowly, many people don’t notice symptoms of the disease for months or even years.

Many of these symptoms, especially fatigue and weight gain, are common and don’t always mean that someone has a thyroid problem.

What causes hypothyroidism?

Hypothyroidism has several causes, including

  • Hashimoto’s disease
  • thyroiditis, or inflammation of the thyroid
  • congenital hypothyroidism, or hypothyroidism that is present at birth
  • surgical removal of part or all of the thyroid
  • radiation treatment of the thyroid
  • some medicines

Less often, hypothyroidism is caused by too much or too little iodine in the diet or by pituitary disease.

Hashimoto’s Disease

Hashimoto’s disease is the most common cause of hypothyroidism. Hashimoto’s disease is an autoimmune disorder. With this disease, your immune system attacks the thyroid. The thyroid becomes inflamed and can’t make enough thyroid hormones.


Thyroiditis is inflammation of your thyroid that causes stored thyroid hormone to leak out of your thyroid gland. At first, the leakage increases hormone levels in the blood, leading to hyperthyroidism, a condition in which thyroid hormone levels are too high. The hyperthyroidism may last for up to 3 months, after which your thyroid may become underactive. The resulting hypothyroidism usually lasts 12 to 18 months, but sometimes is permanent.

Several types of thyroiditis can cause hyperthyroidism and then cause hypothyroidism:

  • Subacute thyroiditis. This condition involves a painfully inflamed and enlarged thyroid. Experts are not sure what causes subacute thyroiditis, but it may be related to an infection caused by a virus or bacteria.
  • Postpartum thyroiditis. This type of thyroiditis develops after a woman gives birth.
  • Silent thyroiditis. This type of thyroiditis is called “silent” because it is painless, even though your thyroid may be enlarged. Experts think silent thyroiditis is probably an autoimmune condition.

Congenital hypothyroidism

Some babies are born with a thyroid that is not fully developed or does not function properly. If untreated, congenital hypothyroidism can lead to intellectual disability and growth failure—when a baby doesn’t grow as expected. Early treatment can prevent these problems, which is why most newborns in the United States are tested for hypothyroidism.

Surgical removal of part or all of the thyroid

When surgeons remove part of the thyroid, the remaining part may produce normal amounts of thyroid hormone, but some people who have this surgery develop hypothyroidism. Removal of the entire thyroid always results in hypothyroidism.

Surgeons may remove part or all of the thyroid as a treatment for

  • hyperthyroidism
  • a large goiter
  • thyroid nodules, which are noncancerous tumors or lumps in the thyroid that can produce too much thyroid hormone
  • thyroid cancer

Radiation treatment of the thyroid

Radioactive iodine, a common treatment for hyperthyroidism, gradually destroys the cells of the thyroid. Most people who receive radioactive iodine treatment eventually develop hypothyroidism. Doctors treat people with head or neck cancers with radiation, which can also damage the thyroid.


Some medicines can interfere with thyroid hormone production and lead to hypothyroidism, including

  • amiodarone, a heart medicine
  • interferon alpha, a cancer medicine
  • lithium, a bipolar disorder medicine
  • interleukin-2, a kidney cancer medicine

How do doctors diagnose hypothyroidism?

Your doctor will take a medical history and do a physical exam, but also will need to do some tests to confirm a diagnosis of hypothyroidism. Many symptoms of hypothyroidism are the same as those of other diseases, so doctors usually can’t diagnose hyperthyroidism based on symptoms alone.

Because hypothyroidism can cause fertility problems, women who have trouble getting pregnant often get tested for thyroid problems.

Your doctor may use several blood tests to confirm a diagnosis of hypothyroidism and find its cause. Learn more about thyroid tests and what the results mean.

How is hypothyroidism treated?

Hypothyroidism is treated by replacing the hormone that your own thyroid can no longer make. You will take levothyroxine, a thyroid hormone medicine that is identical to a hormone the thyroid normally makes. Your doctor may recommend taking the medicine in the morning before eating.

Your doctor will give you a blood test about 6 to 8 weeks after you begin taking thyroid hormone and adjust your dose if needed. Each time your dose is adjusted, you’ll have another blood test. Once you’ve reached a dose that’s working for you, your health care provider will probably repeat the blood test in 6 months and then once a year.

Your hypothyroidism most likely can be completely controlled with thyroid hormone medicine, as long as you take the recommended dose as instructed. Never stop taking your medicine without talking with your health care provider first.

What should I eat or avoid eating if I have hypothyroidism?

The thyroid uses iodine to make thyroid hormones. However, people with Hashimoto’s disease or other types of autoimmune thyroid disorders may be sensitive to harmful side effects from iodine. Eating foods that have large amounts of iodine—such as kelp, dulse, or other kinds of seaweed—may cause or worsen hypothyroidism. Taking iodine supplements can have the same effect.

Talk with members of your health care team about what foods you should limit or avoid, and let them know if you take iodine supplements. Also, share information about any cough syrups that you take because they may contain iodine.

Women need more iodine when they are pregnant because the baby gets iodine from the mother’s diet. If you are pregnant, talk with your health care provider about how much iodine you need.

1Garber JR, Cobin RH, Garib H, et al. Clinical Practice Guidelines for Hypothyroidism in Adults: Cosponsored by the American Association of Clinical Endocrinologists and the American Thyroid Association. Endocrine Practice. 2012;18(6): 988–1028.

This content is provided as a service of the National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK), part of the National Institutes of Health. The NIDDK translates and disseminates research findings through its clearinghouses and education programs to increase knowledge and understanding about health and disease among patients, health professionals, and the public. Content produced by the NIDDK is carefully reviewed by NIDDK scientists and other experts.

The NIDDK would like to thank:
Leonard Wartofsky, M.D., M.A.C.P., Washington Hospital Center and Georgetown University Hospital

This information is not copyrighted. The NIDDK encourages people to share this content freely.

July 2016