Medically Reviewed By William C. Lloyd III, MD, FACS

What is hypothyroidism?

Hypothyroidism is a common disorder that occurs when the thyroid gland is underactive and does not produce enough thyroid hormone. The thyroid gland is located in the front part of the neck. It releases hormones that regulate your metabolism and how you use energy. Other names for hypothyroidism include myxedema, hypothyroid, or underactive thyroid.

A lack of thyroid hormone slows the body’s chemical processes and metabolism. This leads to hypothyroidism symptoms, such as fatigue and weight gain. Hypothyroidism is more common in women than in men. It is also more common in people older than 50 years of age.

Hypothyroidism is not curable, but it is treatable. Left untreated, it may lead to serious, potentially life-threatening complications, such as heart disease and rarely, myxedema coma. Seek prompt medical care if you have symptoms of hypothyroidism, such as cold hands and feet, fatigue, and weight gain. Timely diagnosis and treatment of hypothyroidism reduces the risk of serious complications.

What are the symptoms of hypothyroidism?

The types and severity of hypothyroidism symptoms vary. Many are associated with other conditions. At the onset of the disease, hypothyroidism causes symptoms that can be vague and develop or progress slowly. Symptoms may include:

Later symptoms of undiagnosed or untreated hypothyroidism can include:

  • Bradycardia (slow heartbeat)

  • Depression

  • Enlargement of the tongue

  • Slowing of speech

  • Swelling of the arms or legs

  • Swelling of the hands, feet or face

  • Thickening skin

  • Thinning eyebrows

Serious symptoms that might indicate a life-threatening condition

Any of the following symptoms can indicate worsening of hypothyroidism and a serious or possibly life-threatening situation. Seek immediate medical care (call 911) for any of these symptoms:

What causes hypothyroidism?

Hypothyroidism can be caused by a variety of diseases and conditions. Most commonly, hypothyroidism is the result of inflammation of the thyroid gland, which can be due to:

  • Hashimoto’s thyroiditis, an autoimmune disease in which the body’s immune system mistakes healthy thyroid tissue as potentially dangerous to the body and attacks it. This results in inflammation of the tissue that eventually can destroy the function of the thyroid gland.

  • Viral infection of the thyroid gland (viral thyroiditis)

Hypothyroidism can also be caused by:

  • Birth defects, such as being born without a thyroid gland or with an abnormal thyroid gland

  • Disorders of the pituitary gland or the hypothalamus, which are glands that control the function of the thyroid gland

  • Radiation treatments of the neck

  • Treatments for hyperthyroidism that suppress thyroid hormone secretion

What are the risk factors for hypothyroidism?

A number of factors can put you at risk of developing hypothyroidism. Not all people who are at risk for hypothyroidism will develop the disease. Risk factors include:

  • Autoimmune diseases

  • Family history of hypothyroidism

  • Female sex, especially women over 50 years old

  • Increasing age

  • Pregnancy in the last six months

  • Radiation therapy to the neck or chest

  • Treatment for hyperthyroidism, including radioactive iodine and thyroid surgery

How do you prevent hypothyroidism?

Disease prevention relies on changing risk factors that are under your control. The risk factors for hypothyroidism are not modifiable. So, it is generally not possible to prevent hypothyroidism.

What are the diet and nutrition tips for hypothyroidism?

The thyroid gland needs iodine to make thyroid hormone. Having an iodine deficiency can lead to low thyroid hormone levels. However, people in developed countries rarely have an iodine deficiency. This is due to iodine supplementation of salt and foods. In the United States, eating a balanced diet should ensure you get enough iodine in your diet.

On the other hand, eating too much iodine can be detrimental for people with thyroid disease. If you have questions or concerns about iodine in your diet, talk with your doctor or dietitian. Ask your healthcare provider for guidance before making significant changes to your diet.

Diet can also have an effect on your thyroid hormone medicine. Certain foods can change the way your body absorbs the medicine. This includes high-fiber foods, soy, walnuts, and cottonseed meal. Antacids, multivitamins, calcium and iron supplements, and some medications can have the same effect. It is best to take thyroid hormone medicine on an empty stomach and to separate it from these foods and drugs by at least four hours. Talk with your doctor or pharmacist about how best to take your thyroid hormone medicine.

What are some conditions related to hypothyroidism?

Hyperthyroidism is another major thyroid condition. In thinking about hypothyroid vs hyperthyroidism, they are basically opposites. Hyperthyroidism is having too much thyroid hormone. It causes a high metabolism and the reverse symptoms. This includes rapid heart rate, weight loss, heat intolerance, sweating, anxiety and irritability.

Ironically, treating each condition can result in the other. Destroying the thyroid gland to manage hyperthyroidism can cause thyroid hormone levels to go too low. Conversely, giving too much thyroid hormone medicine to treat hypothyroidism can cause thyroid hormone levels to go too high. Careful monitoring is necessary to keep hormone levels balanced.

How do doctors diagnose hypothyroidism?

To diagnose hypothyroidism, your doctor will take a medical history, perform an exam, and order testing. Questions your doctor may ask about your symptoms and medical history include:

  • What symptoms are you experiencing?

  • How long have you had these symptoms?

  • Are your symptoms constant or do they come and go?

  • What, if anything, seems to make your symptoms better or worse?

  • Do you have a family history of thyroid disease?

  • What other medical conditions do you have?

  • When was your last menstrual period and are they regular?

  • Are you trying to get pregnant or have you been pregnant in the last six months?

During the physical exam, your doctor will look for signs of hypothyroidism, such as low blood pressure or skin or hair changes. Your doctor will also feel your neck to check the size of your thyroid gland. It may be smaller or larger than normal.

Tests to diagnose hypothyroidism

Symptoms and exam results alone cannot diagnose hypothyroidism. The symptoms are common to other conditions and the exam may be unremarkable. This makes blood tests necessary to diagnose hypothyroidism. Blood tests include:

  • TSH (thyroid stimulating hormone): The pituitary gland makes this hormone. It releases TSH when it monitors thyroid hormone (T4) levels and senses that levels are too low. TSH stimulates the thyroid gland to make T4. TSH is high in hypothyroidism. If the thyroid is not making enough T4, the pituitary will pump out TSH trying to stimulate production. This is the most sensitive test for hypothyroidism.

  • T4 (thyroxine) tests: This group of tests measures the amount of thyroid hormone in the blood. There are both free and protein-bound forms of the hormone. 

Your doctor may also order imaging exams or other blood tests, in some cases.

How do you treat hypothyroidism?

There is no cure for hypothyroidism. However, hypothyroidism treatment can replace low levels of thyroid hormone and achieve normal levels in the body. To accomplish this, most people have to take the oral thyroid hormone replacement medication levothyroxine for the rest of their lives.

Doctors monitor thyroid medication therapy closely with blood tests for several months after beginning hypothyroidism treatment. This ensures you are taking the right amount of the drug. Ideal doses vary among individuals. If the dose is too low, it will not adequately replace thyroid hormone in the body. If the dose is too high, it may result in side effects and a potentially serious condition called hyperthyroidism.

Once your doctor finds a safe and effective dose, you generally need monitoring yearly. If symptoms reappear or side effects develop, you may need monitoring more frequently. It is very important not to skip or change doses of your medication without consulting with your doctor.

If myxedema coma develops, it requires intensive hospital care. Treatment of this life-threatening complication includes IV (intravenous) thyroid hormone and corticosteroids. This care and monitoring usually takes place in a critical care unit.

What are the potential complications of hypothyroidism?

Complications of untreated hypothyroidism can be serious and even life-threatening in some cases. You can minimize the risk of serious complications of hypothyroidism by following the treatment plan you and your healthcare professional design specifically for you.

Complications of untreated hypothyroidism include:

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  1. Collins RD. Differential Diagnosis and Treatment in Primary Care, 6th ed. Philadelphia: Wolters Kluwer, 2018.
  2. Hypothyroid Diet: Can Certain Foods Increase Thyroid Function? Mayo Foundation for Medical Education and Research. https://www.mayoclinic.org/diseases-conditions/hypothyroidism/expert-answers/hypothyroidism-diet/faq-20058554
  3. Hypothyroidism. Cleveland Clinic. https://my.clevelandclinic.org/health/diseases/12120-hypothyroidism
  4. Hypothyroidism. MedlinePlus, National Library of Medicine, National Institutes of Health. http://www.nlm.nih.gov/medlineplus/ency/article/000353.htm
  5. Hypothyroidism (Underactive). American Thyroid Association. https://www.thyroid.org/hypothyroidism/
  6. Hypothyroidism (Underactive Thyroid). Mayo Foundation for Medical Education and Research. https://www.mayoclinic.org/diseases-conditions/hypothyroidism/symptoms-causes/syc-20350284
  7. Hypothyroidism (Underactive Thyroid). National Institute of Diabetes and Digestive and Kidney Diseases. https://www.niddk.nih.gov/health-information/endocrine-diseases/hypothyroidism#diagnosis
  8. Kellerman RD, Raker DP (Eds.) Conn’s Current Therapy, 72d ed. Philadelphia: Elsevier, 2020.
Medical Reviewer: William C. Lloyd III, MD, FACS
Last Review Date: 2021 Oct 6
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