The thyroid gland is a butterfly-shaped gland in the front of the neck. Hypothyroidism is a condition in which the thyroid gland does not produce enough thyroid hormones. A healthy thyroid produces the hormones thyroxine (T4) and triiodothyronine (T3), which control metabolism. This affects how many calories you burn, how warm you feel, how much you weigh, and how the body handles functions of the cardiovascular, gastrointestinal, and nervous systems. Hypothyroidism results in a slower metabolism and a slower heartbeat.

The Thyroid Gland

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Hashimoto's thyroiditis occurs when the immune system produces antibodies that attack cells of the thyroid gland. This results in thyroid swelling. Other less common causes include hypothyroidism as a result of neck radiation for lymphoma and treatment of hyperthyroidism or thyroid cancer with radioactive iodine or surgery.

Other causes of hypothyroidism include:

• Subacute thyroiditis —This occurs when there is inflammation of the thyroid gland after a viral upper respiratory tract infection.
• Drugs —Drugs used to treat hyperthyroidism such as lithium (used to treat certain psychiatric disorders), certain cardiac medicines, and other medicines (interleukins, alpha interferon)
• Medical treatments —Treatments include radiation or surgical removal of part of the thyroid gland (called subtotal thyroidectomy) to treat other thyroid diseases
• Idiopathic thyroid atrophy —The thyroid tissue shrivels up (atrophies) for unknown reasons
• Iodine deficiency —The thyroid gland does not get enough iodine to produce thyroid hormone (this is rare in the United States)
• Iodine excess —Certain foods (such as shellfish) and certain medicines (such as cough medicine) contain large amounts of iodine, which can block thyroid hormone production (rare)
• Infiltrative illnesses —Cancers and certain infections
• Pituitary adenoma —A benign tumor of the pituitary gland that can cause a problem signaling the thyroid to make thyroid hormones
• Postpartum thyroiditis —This condition usually improves but may be long lasting
• Congenital hypothyroidism —An infant that is born with problems making normal amounts of thyroid hormones

About 5% of Americans have hypothyroidism. This condition usually occurs in adults. But, in some cases, children or infants may have hypothyroidism (called cretinism). Children need treatment as quickly as possible or intellectual disability may result.