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Causes of Underactive Thyroid

Medications
Some drugs can interfere with thyroid hormone production and lead to an underactive thyroid. These drugs include:
Iodine Deficiency or Excess
Both iodine deficiency and, in some cases, excess iodine can result in an underactive thyroid. Iodine deficiency is rare in the United States because our salt is iodized. On the other hand, iodine deficiency is the leading cause of hypothyroidism worldwide, affecting about two billion people.
Certain people can develop an underactive thyroid by consuming too much iodine. This is really not an issue for most people, however, because the body quickly gets rid of excess iodine. Iodine-induced hypothyroidism can be a possible problem for people:
  • With Hashimoto's thyroiditis, subacute thyroiditis, or postpartum thyroiditis
  • Who have had part or all of the thyroid gland removed surgically
  • Undergoing radiation treatment of the thyroid
  • With thyroiditis in general.
If these people consume excess iodine for more than a couple of days, they can increase their chances of developing an underactive thyroid. This excess iodine can come from a number of different places, including cough medicines, dietary supplements, and other iodine-containing substances.

Secondary Hypothyroidism Causes

Problems with the pituitary gland can cause secondary hypothyroidism. Examples include:
  • A pituitary tumor (up to 25 percent of people with pituitary macroadenomas will develop hypothyroidism)
  • Other types of tumors
  • Damage to the pituitary gland from radiation therapy
  • Postpartum pituitary necrosis (Sheehan's syndrome)
  • Trauma
  • A mutation to the gene that creates TSH or the TSH receptor.
Last reviewed by: Arthur Schoenstadt, MD
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