Methimazole prevents the thyroid gland from producing too much thyroid hormone.

Methimazole is used to treat hyperthyroidism (overactive thyroid). It is also used before thyroid surgery or radioactive iodine treatment.

Methimazole may also be used for other purposes not listed in this medication guide.

Do not use methimazole if you are pregnant. It could harm the unborn baby.

Do not take methimazole if you are breast-feeding a baby.

Methimazole can increase your risk of bleeding. If you need to have surgery, tell the surgeon ahead of time that you are using this medication.

Methimazole can lower blood cells that help your body fight infections. This can make it easier for you to bleed from an injury or get sick from being around others who are ill. Your blood may need to be tested often. Visit your doctor regularly.

Do not receive a "live" vaccine while you are being treated with methimazole, and avoid coming into contact with anyone who has recently received a live vaccine. There is a chance that the virus could be passed on to you.

Keep using this medication even if you feel fine or have no symptoms of hyperthyroidism. You may need to keep taking methimazole long term to control your condition. Stopping the medication could cause your symptoms to return.

Do not use this medication if you are allergic to methimazole.

If you have any of these other conditions, you may need a dose adjustment or special tests to safely take this medication:

• liver disease;

• a blood cell disorder; or

• a weak immune system.

FDA pregnancy category D. Do not use methimazole if you are pregnant. It could harm the unborn baby. Use effective birth control, and tell your doctor if you become pregnant during treatment.

Methimazole can pass into breast milk and may harm a nursing baby. Do not use methimazole if you are breast-feeding a baby.