What causes hyperthyroidism?

The most common cause of hyperthyroidism is Graves’ disease, an autoimmune condition in which the immune system produces antibodies that stimulate the thyroid gland to produce too much thyroid hormone. Other causes of hyperthyroidism include toxic multinodular goiter, toxic adenomas, and thyroid cancer. Some medications, such as amiodarone, lithium, and tyrosine-kinase inhibitors, may also cause hyperthyroidism.^[1] In some instances, people with hypothyroid who are being treated with thyroid hormone replacement medication may also develop hyperthyroidism.