What is methimazole and what condition does it treat?

Methimazole is an antithyroid medication used to treat hyperthyroidism, most commonly Graves disease. It works by inhibiting thyroid peroxidase, the enzyme that incorporates iodine into thyroid hormones, thereby reducing the production of T3 and T4. Methimazole is preferred over propylthiouracil for most patients because of its longer duration of action and lower risk of liver damage. The most serious adverse effect is agranulocytosis, a dangerous drop in white blood cells that occurs in less than 1 percent of patients.