When you are hyperthyroid, your thyroid is producing too much thyroid hormone, or you are being exposed to too much thyroid hormone. Hyperthyroidism has a number of causes.
In autoimmune disease, your body manufactures antibodies to attack your own tissues, glands, organs, and cells. In Graves' disease, antibodies target your thyroid and cause it to overproduce thyroid hormone, making you hyperthyroid. Less commonly, Hashimoto's thyroiditis can cause periods of hyperthyroidism, alternating with hypothyroidism.
In addition to Hashimoto’s thyroiditis, other forms of thyroiditis — conditions that involve inflammation of the thyroid gland — can cause hyperthyroidism.
Plummer’s disease/toxic multinodular goiter
Plummer’s disease, also known as toxic multinodular goiter, is a condition where the thyroid is enlarged and contains multiple thyroid nodules. The nodules are capable of producing thyroid hormone, apart from the gland itself, and this overproduction of thyroid hormone results in hyperthyroidism.
Taking too much thyroid hormone replacement medication (such as Synthroid, Levoxyl, Nature-throid, or Armour Thyroid) — or taking it when it is not prescribed or needed — can cause hyperthyroidism. Pharmacy errors and unusual potency fluctuations in thyroid drugs may also end up causing overmedication and hyperthyroidism.
In some cases, babies born to mothers who have high levels of thyroid stimulating immunoglobulin (TSI) antibodies are also born with high levels of those antibodies and are hyperthyroid. Neonatal hyperthyroidism usually resolves after several months as the antibody levels drop after birth.
Excessive exposure to iodine can cause hyperthyroidism. Overexposure to iodine can be due to overconsumption of iodine-rich foods, use of iodine supplements or supplements that contain iodine (including bladderwrack, kelp, and some thyroid support formulas), external iodine (i.e., povidone/Betadine solution), or intravenous iodine contrast agents used for diagnostic medical tests.
According to the 2016 American Thyroid Association Guidelines for Diagnosis and Management of Hyperthyroidism, a number of prescription drugs can cause hyperthyroidism. Some of these drugs include:
- Interferon Beta-1b
- Immunosuppressant therapy
- Antiretroviral treatment for AIDS
- Monoclonal antibody (Campath-1H), for multiple sclerosis
Receiving a donated organ or bone marrow transplant
Receiving an organ or bone marrow donation from someone with Graves’ disease can cause Graves’ disease and hyperthyroidism in the recipient.
A number of supplements can cause hyperthyroidism, including:
- Thyroid support, diet, and energy supplements that are high in iodine, such as kelp or bladderwrack
- Thyroid support, diet, and energy supplements that contain undisclosed amounts of actual thyroid hormone
- Iodine supplements, such as Iodoral or Lugol’s solution
Some integrative and holistic practitioners have theorized other causes for hyperthyroidism and Graves’ disease, including:
In some cases, your thyroid gland can become overactive, but there is no identifiable cause, trigger, or disease your practitioner can identify. This is known as idiopathic hyperthyroidism.