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Hypothyroidism, also called underactive thyroid or low thyroid, is a disorder of the endocrine system in which the thyroid gland does not produce enough thyroid hormone.[1] 100px|left


It can cause a number of symptoms, such as poor ability to tolerate cold, a feeling of tiredness, constipation, depression, and weight gain.[1] 100px|left

Neck swelling

Occasionally there may be swelling of the front part of the neck due to goiter.[1] 100px|left

Untreated effects during pregnancy

Untreated hypothyroidism during pregnancy can lead to delays in growth and intellectual development in the baby or congenital iodine deficiency syndrome.[2] 100px|left


Worldwide, too little iodine in the diet is the most common cause of hypothyroidism.[3][4] 100px|left


In countries with enough iodine in the diet, the most common cause of hypothyroidism is the autoimmune condition Hashimoto's thyroiditis.[1] 100px|left

Infrequent causes

Less common causes include: previous treatment with radioactive iodine, injury to the hypothalamus or the anterior pituitary gland, certain medications, a lack of a functioning thyroid at birth, or previous thyroid surgery.[1][5] 100px|left


The diagnosis of hypothyroidism, when suspected, can be confirmed with blood tests measuring thyroid-stimulating hormone (TSH) and thyroxine levels.[1] People over the age of 60 are more commonly affected.[1] 100px|left


Salt iodization has prevented hypothyroidism in many populations.[6] Hypothyroidism can be treated with levothyroxine.[1] 100px|left

Adjusting dose

The dose is adjusted according to symptoms and normalization of the thyroxine and TSH levels.[1] Thyroid medication is safe in pregnancy.[1] 100px|left

Effect of excess iodine

While a certain amount of dietary iodine is important, excessive amounts can worsen certain types of hypothyroidism.[1] 100px|left


Worldwide about one billion people are estimated to be iodine deficient; however, it is unknown how often this results in hypothyroidism.[7] 100px|left

Burden in the US

In the United States, hypothyroidism occurs in 0.3–0.4% of people.[3] People over the age of 60 are more commonly affected.[1] Hypothyroidism is more common in women than men.[1] 100px|left

Subclinical hypothyroidism rate

Subclinical hypothyroidism, a milder form of hypothyroidism characterized by normal thyroxine levels and an elevated TSH level, is thought to occur in 4.3–8.5% of people in the United States.[3] 100px|left

Other animals

Dogs are also known to develop hypothyroidism and in rare cases cats and horses.[8] 100px|left


The word "hypothyroidism" is from Greek hypo- meaning "reduced", thyreos for "shield", and eidos for "form".[9] 100px|left

  1. 1.00 1.01 1.02 1.03 1.04 1.05 1.06 1.07 1.08 1.09 1.10 1.11 1.12 "Hypothyroidism". National Institute of Diabetes and Digestive and Kidney Diseases. March 2013. Archived from the original on 5 March 2016. Retrieved 5 March 2016.
  2. Preedy, Victor (2009). Comprehensive Handbook of Iodine Nutritional, Biochemical, Pathological and Therapeutic Aspects. Burlington: Elsevier. p. 616. ISBN 9780080920863.
  3. 3.0 3.1 3.2 Garber JR, Cobin RH, Gharib H, Hennessey JV, Klein I, Mechanick JI, Pessah-Pollack R, Singer PA, Woeber KA (December 2012). "Clinical practice guidelines for hypothyroidism in adults: cosponsored by the American Association of Clinical Endocrinologists and the American Thyroid Association" (PDF). Thyroid. 22 (12): 1200–35. doi:10.1089/thy.2012.0205. PMID 22954017. Archived (PDF) from the original on 2016-01-14.
  4. Chakera AJ, Pearce SH, Vaidya B (2012). "Treatment for primary hypothyroidism: current approaches and future possibilities". Drug Design, Development and Therapy (Review). 6: 1–11. doi:10.2147/DDDT.S12894. PMC 3267517. PMID 22291465.
  5. Persani L (September 2012). "Clinical review: Central hypothyroidism: pathogenic, diagnostic, and therapeutic challenges". The Journal of Clinical Endocrinology and Metabolism (Review). 97 (9): 3068–78. doi:10.1210/jc.2012-1616. PMID 22851492.
  6. Syed S (April 2015). "Iodine and the "near" eradication of cretinism". Pediatrics. 135 (4): 594–6. doi:10.1542/peds.2014-3718. PMID 25825529. S2CID 27647943.
  7. Cooper, DS; Braverman LE, eds. (2012-07-12). Werner & Ingbar's the thyroid : a fundamental and clinical text (10th ed.). Philadelphia: Wolters Kluwer/Lippincott Williams & Wilkins Health. p. 552. ISBN 978-1451120639. Archived from the original on 2016-05-20.
  8. "Hypothyroidism". Merck Veterinary Manual, 10th edition (online version). 2012. Archived from the original on 2012-08-23. Retrieved 2013-12-25.
  9. Mosby's Medical Dictionary (9 ed.). Elsevier Health Sciences. 2013. p. 887. ISBN 9780323112581. Archived from the original on 2016-03-07.