Font Size

Medications and Drugs

Brand Names: Northyx, Tapazole

Generic Name: methimazole (Pronunciation: me THIM a zole)

What is methimazole (Northyx, Tapazole)?

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.

Methimazole 10 mg-EON

round, white, imprinted with E 210

Methimazole 10 mg-MUT

round, white, imprinted with XM

Methimazole 5 mg-EON

round, white, imprinted with E 205

Methimazole 5 mg-MUT

round, white, imprinted with VM

Methimazole 5 mg-PAR

round, white, imprinted with MP 751

Tapazole 10 mg

round, white, imprinted with J95

Tapazole 5 mg

round, white, imprinted with J94

What are the possible side effects of methimazole (Northyx, Tapazole)?

Get emergency medical help if you have any of these signs of an allergic reaction: hives; difficulty breathing; swelling of your face, lips, tongue, or throat.

Stop using methimazole and call your doctor at once if you have a serious side effect such as:

  • fever, chills, sore throat, body aches, flu symptoms;
  • easy bruising or bleeding, unusual weakness;
  • blood in your urine or stools;
  • severe blistering, peeling, and red skin rash; or
  • nausea, stomach pain, low fever, loss of appetite, dark urine, clay-colored stools, jaundice (yellowing of the skin or eyes).

Less serious side effects may include:

  • headache, drowsiness, dizziness;
  • mild nausea, vomiting, or stomach upset;
  • itching, minor skin rash;
  • muscle, joint, or nerve pain;
  • swelling; or
  • hair loss.

This is not a complete list of side effects and others may occur. Call your doctor for medical advice about side effects. You may report side effects to FDA at 1-800-FDA-1088.

What is the most important information I should know about methimazole (Northyx, Tapazole)?

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.

Report Problems to the Food and Drug Administration

You are encouraged to report negative side effects of prescription drugs to the FDA. Visit the FDA MedWatch website or call 1-800-FDA-1088.

Pill Identifier Tool

Need help identifying pills and medications?
Use the pill finder tool on RxList.

Medical Dictionary