What causes hypothyroidism?

The most common cause of hypothyroidism in the U.S. is Hashimoto’s thyroiditis, while in other countries it is iodine deficiency. Certain drugs and therapies can also precipitate hypothyroidism. Some examples include amiodarone, oral tyrosine kinase inhibitors, interferon, bexarotene, rifampin, phenobarbital, phenytoin, carbamazepine, interleukin-2, lithium, radioactive iodine therapy, radiation exposure, and thyroid surgery. Hypothyroidism can also be caused by disorders of the pituitary gland (secondary hypothyroidism) or hypothalamus (tertiary hypothyroidism).^[1]