Drugs can affect thyroid function at any level. They can increase or decrease the release of thyrotrophin-releasing hormone, which affects how much thyroid-stimulating hormone (TSH) your body creates. They can increase or decrease the release of thyroid hormone from the thyroid. They can change the ratio of T4 hormone versus T3. They can affect the uptake of thyroid hormone by cells. They can increase or decrease the action of thyroid hormone within the cells. The major drugs that you should be concerned about are the following, which I discuss in Chapter 10: Lithium Amiodarone Estrogen Steroids Aspirin (in doses greater than 3,000 milligrams) Iron tablets Iodine Propranolol Chances are that you’ll take one or more of these drugs in your lifetime. Just about every drug affects thyroid function in one way or another. Fortunately, your thyroid gland makes some adjustment to overcome most of the effects. But if you’re on a fixed treatment dose of thyroid hormone, your thyroid can’t adjust as it would normally. Having your thyroid function tested four to six weeks after you start a new medication or stop an old one is wise.
Protecting Your Thyroid from Radiation One million or more Americans received neck irradiation for various conditions in the years between 1920 and 1960, and they’re at higher risk for thyroid cancer. Close to 10 percent of people who were so treated have developed thyroid cancer to date. If you received irradiation to your neck area as a child because of enlarged tonsils, acne, an enlarged thymus, or some other condition, you’re at increased risk for thyroid cancer and should inform your doctor.