Never thought about your thyroid gland? You might have to after starting prescriptions for completely unrelated conditions.
Most people who have an under-performing thyroid gland, known as hypothyroidism, got the disease because their immune system started attacking their thyroid gland. However, hypothyroidism can also be triggered by certain medications for unrelated conditions.
On Lithium? Check Your Thyroid
A common offender is lithium, especially in people who have an underlying or undiagnosed thyroid problem, said Leonard Wartofsky, MD, MPH, chairman of the department of medicine at MedStar Washington Hospital Center in Washington, D.C.
Lithium, primarily to treat episodes of mania in people with bipolar disorder, works by decreasing abnormal activity in the brain. It is also prescribed for certain blood disorders, depression, and schizophrenia.
Anyone prescribed lithium should have their thyroid blood levels checked regularly to make sure there is no lithium-induced hypothyroidism.
If the thyroid gland is functioning normally, lithium used to treat these other conditions should have no effect on the amount of thyroid hormone released, Dr. Wartofsky said. But if you have Hashimoto’s, another subclinical thyroid disorder, or even a genetic predisposition to hypothyroidism, “lithium becomes a great burden to the gland that cannot be overcome.”
Iodine: Too Much of a Good Thing Is No Good
The thyroid gland needs iodine to function properly.
According to a 2012 paper published in the journal Endocrine Practice, iodine deficiency is the most common cause of hypothyroidism in the world.
However, in the United States and other developed countries, there is usually plenty of iodine in the basic diet to keep the thyroid functioning normally.
Even though the thyroid needs iodine, “too much of a good thing is no good,” Wartofsky said. Iodine supplements — often seaweed-based and offered as a powder, tablet, or capsule — are advised only for people diagnosed with iodine deficiency. For anyone else, the iodine intake can become excessive and affect thyroid function, especially if you are predisposed to the disease either through genetics or a subclinical condition.
Other Drugs and Hypothyroidism
Other, less common medications that can lead to hypothyroidism in people already predisposed include:
Amiodarone: most commonly prescribed for heart rhythm disorders and containing large amounts of iodine, it also can cause thyroid inflammation that initially causes thyroid hormone levels to rise, explained Jeffrey Garber, MD, associate professor of medicine at Harvard Medical School, immediate past president of the American College of Endocrinology, and chief of endocrinology at Harvard Vanguard Medical Associates in Boston. “After this resolves, the thyroid gland is depleted and hypothyroidism, which may or may not be permanent, ensues.”
Interferon alpha: Used to treat hepatitis C and some cancers, Dr. Garber said that it may cause inflammation of the thyroid gland, known as thyroiditis, which can lead to hypothyroidism.
Interleukin-2:Used to boost the immune system in cancer therapy, it can cause thyroiditis.
Thalidomide: Although the onset of hypothyroidism from this cancer drug used to treat multiple myeloma is rare, thalidomide also may cause thyroiditis, Garber said.
Bexarotene: best known for treating for cutaneous T cell lymphoma.
Ipilimumab: used to treat melanoma by activating the immune system.
Tyrosine kinase inhibitors: including the cancer drugs sunitinib and sorafenib.
Since several medications can lead to diseases of the thyroid, Garber advised patients to help protect themselves by asking their doctor whether a prescribed medication could possibly interfere with thyroid function before taking it.
