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Condition Basics

What is hypothyroidism?

Hypothyroidism means that the thyroid gland doesn't make enough thyroid hormone. This hormone controls the way your body uses energy. The thyroid is a butterfly-shaped gland in the front of your neck.

Having a low level of thyroid hormone affects your whole body. It can make you feel tired and weak. If it isn't treated, it can raise your cholesterol levels. During pregnancy, untreated hypothyroidism can harm your baby. But low thyroid levels can be treated with medicine that can help you feel like yourself again.

People of any age can get hypothyroidism, but older adults are more likely to get it. Women age 60 and older have the highest risk. You are more likely to get the disease if it runs in your family.

What causes it?

In the United States, the most common cause of hypothyroidism is Hashimoto's thyroiditis. It causes the body's immune system to attack thyroid tissue. As a result, the gland can't make enough thyroid hormone. Worldwide, iodine deficiency is the number one cause of hypothyroidism.

What are the symptoms?

If you have low thyroid levels, you may feel tired, weak, or depressed. Other symptoms include dry skin, brittle nails, not being able to stand the cold, constipation, memory problems, and heavy or irregular menstrual periods. Symptoms occur slowly over time. You might not notice them or might mistake them for normal aging.

How is it diagnosed?

To diagnose hypothyroidism, your doctor will first ask you about your past health problems and do a physical exam. If your doctor thinks you have the condition, a simple blood test can show if your thyroid hormone level is too low.

How is hypothyroidism treated?

Hypothyroidism is treated with thyroid pills. Your symptoms will probably go away within a few months. But you will likely need to keep taking the pills. You will also need regular follow-up visits to make sure you have the right dose. If your condition is mild, you may not need treatment right away.


In the United States, the most common cause is Hashimoto's thyroiditis.

Worldwide, iodine deficiency is the number one cause of low thyroid levels.

Other common causes include:

  • Thyroid surgery.
  • Radioactive iodine therapy.
  • External beam radiation. This is used to treat some cancers, such as Hodgkin lymphoma.

Less common causes

Less common causes include:

  • Infections.
  • Some medicines, such as lithium.
  • Disorders of the pituitary gland or the hypothalamus.
  • Consuming too much iodine.
  • Being born with a thyroid gland that doesn't work right. (This is called congenital hypothyroidism.)

Learn more

What Increases Your Risk

Many things may increase your risk for hypothyroidism. These include:

Age and being female.

Older adults are more likely to develop hypothyroidism than younger people. And women are more likely than men to develop thyroid disease.

Family history.

Hypothyroidism tends to run in families.

Previous thyroid problems.

Thyroid disease, an enlarged thyroid (goiter), and surgery or radiation therapy to treat thyroid problems increase the likelihood of having hypothyroidism in the future.

Some lifelong conditions.

Type 1 diabetes, vitiligo (an autoimmune disease that causes patches of light skin), pernicious anemia, and leukotrichia (premature gray hair) are seen more often in people who have hypothyroidism.

Iodine deficiency.

This is rare in the United States but common in areas where iodine is not added to salt, food, and water.


Some medicines can interfere with normal thyroid function, particularly lithium or amiodarone.


Low thyroid levels can cause many different symptoms, including:

  • Feeling tired, weak, or depressed.
  • Dry skin and brittle nails.
  • Not being able to stand the cold.
  • Constipation.
  • Memory problems or trouble thinking clearly.
  • Heavy or irregular menstrual periods.

Symptoms occur slowly over time. At first you might not notice them, or you might mistake them for normal aging.

Symptoms in infants, children, teens, and pregnant women

Although rare, hypothyroidism can occur in infants, children, and teens. In infants, symptoms include a poor appetite and choking on food. Symptoms may also include dry, scaly skin. In children and teens, symptoms include behavior problems and changes in school performance. Children and teens may gain weight but have a slowed growth rate. Teens may have delayed puberty and look much younger than their age.

Symptoms of hypothyroidism during and after pregnancy include fatigue, weight loss, dizziness, depression, and memory and concentration problems.

What Happens

Hypothyroidism caused by Hashimoto's thyroiditis sometimes goes away on its own. More often it causes gradual loss of thyroid function. Symptoms may develop slowly and be mild. But symptoms usually grow worse, and health problems may develop over time.

If untreated, hypothyroidism may lead to myxedema. This condition causes swelling of tissues, increased fluid around the heart and lungs, slowed muscle reflexes, and a slowed ability to think. In rare cases, it can cause a coma which can be life-threatening.

People with mild (subclinical) hypothyroidism have only slightly abnormal thyroid blood test results and often do not have obvious symptoms or health problems. Some people who have mild hypothyroidism regain normal thyroid function.

If your thyroid gland has been removed during surgery, hypothyroidism will occur within a few weeks. If you have been treated with radioactive iodine therapy, hypothyroidism may develop within a year. In these cases, thyroid function typically doesn't return.

Hypothyroidism in infants and children

Although rare, hypothyroidism can occur in infants and children. If hypothyroidism is treated within the first month of life, a child will grow and develop normally. Untreated hypothyroidism in infants can cause brain damage, leading to intellectual disability and developmental delays. In the United States, all children are tested for hypothyroidism at birth.

Intellectual disability usually does not occur if hypothyroidism develops after age 3. But untreated childhood hypothyroidism typically delays physical growth and sexual development, including the onset of puberty. Children may gain weight yet have a slowed growth rate.

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When to Call a Doctor

Call 911 or other emergency services immediately if you or a person you know has hypothyroidism and has signs of myxedema coma, such as:

  • Mental deterioration, such as apathy, confusion, or psychosis.
  • Extreme weakness and fatigue that progress to loss of consciousness (coma).
  • Severe trouble breathing, slow heart rate (less than 60 beats per minute), or low body temperature [95°F (35°C) or below].

See your doctor if you have any symptoms that don't go away, including:

  • Depression.
  • Feeling tired, sluggish, or weak.
  • Memory problems or trouble concentrating.
  • An inability to tolerate cold.
  • Dry skin, brittle nails, or a yellowish tint to the skin.
  • Constipation.
  • Heavy or irregular menstrual periods that may last longer than 5 to 7 days.

If you have one or two of the above symptoms that have not changed or have changed very little over a long period of time, it's less likely that the symptoms are caused by hypothyroidism. Consult your doctor.

Talk to a doctor if you are pregnant and have some of the above symptoms. Also talk to a doctor if you have hypothyroidism and are pregnant or are trying to become pregnant. Your dose of thyroid hormone medicine may need to be changed.

Watchful waiting

Watchful waiting is a wait-and-see approach. It's not a good choice for hypothyroidism that is causing symptoms. Treatment should start as soon as the condition is diagnosed.

Watchful waiting may be okay for certain adults with mild (subclinical) hypothyroidism whose blood tests show only small changes. Talk to your doctor about treatment, its cost, and possible risks and benefits. Watch for any signs that your hypothyroidism is getting worse. Doctors often want people to have yearly thyroid function blood tests to check to see if thyroid hormone production is normal.

Exams and Tests

To diagnose hypothyroidism, your doctor will first ask you about your past health problems and do a physical exam. If your doctor thinks you have the condition, a simple blood test can show if your thyroid hormone level is too low. The blood tests used most often are:

  • Thyroid-stimulating hormone (TSH) test.
  • Thyroxine (T4) measurement.

If the results of the above tests aren't normal, you may have antithyroid antibody tests. These tests can tell if you have the autoimmune disease Hashimoto's thyroiditis. When you have this disease, your body's defense system attacks the thyroid gland.

Because hypothyroidism may cause problems with thinking and learning, every state in the U.S. tests newborns for the condition. If your baby wasn't born in a hospital or if you think your baby may not have been tested, talk to your doctor.

Screening for hypothyroidism

Expert groups differ in their recommendations for screening for hypothyroidism. For example:

  • The American Thyroid Association and the American Association of Clinical Endocrinologists recommend that testing be considered for those older than age 60.footnote 1
  • The U.S. Preventive Services Task Force makes no recommendation for or against screening for people who do not have symptoms of thyroid problems. The USPSTF states that there is not enough evidence to support screening.footnote 2

Talk to your doctor about whether testing is right for you.

Learn more


Treatment Overview

Thyroid hormone medicine is the only way to treat hypothyroidism. Your doctor will treat your low thyroid level with the thyroid pills levothyroxine. Usually, thyroid hormone medicine:

  • Reduces or gets rid of symptoms of hypothyroidism. Symptoms often improve within the first week after you begin therapy. All symptoms often go away within a few months.
  • May reduce the risk of slowed physical growth, intellectual disability, and problems with behavior in infants and children.

After you start treatment, you'll have regular visits with your doctor to see if you have the right dose of medicine. Getting too much or too little thyroid hormone can cause problems.

Thyroid hormone medicine does not cause side effects if you take the correct dose. Depending on its cause, people who have hypothyroidism may need treatment for the rest of their lives.

Learn more


  • Take your thyroid hormone medicine exactly as prescribed. Call your doctor if you think you are having a problem with your medicine. Most people do not have side effects if they take the right amount of medicine regularly.
    • Take the medicine 30 minutes before breakfast, and do not take it with calcium, vitamins, or iron.
    • Do not take extra doses of your thyroid medicine. It will not help you get better any faster, and it may cause side effects.
    • If you forget to take a dose, do NOT take a double dose of medicine. Take your usual dose the next day.
  • Tell your doctor about all prescription, herbal, or over-the-counter products you take.
  • Take care of yourself. Eat a healthy diet, get enough sleep, and get regular exercise.

Learn more




  1. Garber JR, et al; American Association of Clinical Endocrinologists and American Thyroid Association Taskforce on Hypothyroidism in Adults (2012). Clinical practice guidelines for hypothyroidism in adults: Cosponsored by the American Association of Clinical Endocrinologists and the American Thyroid Association. Endocrinology Practice, 18(6): 988–1028.
  2. LeFevre ML (2015). Screening for thyroid dysfunction: U.S. Preventive Services Task Force recommendation statement. Annals of Internal Medicine, published online Mar 24, 2015. DOI: 10.7326/M15-0483. Accessed April 10, 2015.


Current as of: October 6, 2021

Author: Healthwise Staff
Medical Review:
Kathleen Romito MD - Family Medicine
E. Gregory Thompson MD - Internal Medicine
Matthew I. Kim MD - Endocrinology

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