Health Library

Methimazole (By mouth)

Methimazole (meth-IM-a-zole)

Treats hyperthyroidism (too much thyroid hormone produced by the thyroid gland).

Brand Name(s):

When This Medicine Should Not Be Used:

How to Use This Medicine:

Tablet

• Your doctor will tell you how much medicine to use. Do not use more than directed.
• Missed dose: Take a dose as soon as you remember. If it is almost time for your next dose, wait until then and take a regular dose. Do not take extra medicine to make up for a missed dose.
• Store the medicine in a closed container at room temperature, away from heat, moisture, and direct light.

Drugs and Foods to Avoid:

Ask your doctor or pharmacist before using any other medicine, including over-the-counter medicines, vitamins, and herbal products.

• Some medicines can affect how methimazole works. Tell your doctor if you are using any of the following:
  • Digitalis, theophylline
  • Beta blockers
  • Blood thinner (including warfarin)

Warnings While Using This Medicine:

• Using this medicine during the first three months of pregnancy can harm your unborn baby. Use an effective form of birth control to keep from getting pregnant. If you think you have become pregnant while using the medicine, tell your doctor right away.
• Tell your doctor if you are breastfeeding, or if you have kidney disease, liver disease, lung disease, or breathing problems.
• This medicine may cause the following problems:
  • Liver problems
  • Hypothyroidism (low levels of thyroid in the blood)
  • Vasculitis (swelling of the blood vessels)
• Make sure any doctor or dentist who treats you knows that you are using this medicine.
• This medicine may make you bleed, bruise, or get infections more easily. Take precautions to prevent illness and injury. Wash your hands often.
• Your doctor will do lab tests at regular visits to check on the effects of this medicine. Keep all appointments.
• Keep all medicine out of the reach of children. Never share your medicine with anyone.

Possible Side Effects While Using This Medicine:

Call your doctor right away if you notice any of these side effects:

• Chest pain or tightness, troubled breathing, coughing up blood
• Dark or bloody urine, pale stools, loss of appetite, stomach pain, yellow skin or eyes
• Fever, chills, cough, sore throat, body aches
• Numbness, tingling, or burning in your hands or feet
• Severe skin rash, redness, or itching
• Unusual bruising, bleeding, or weakness

If you notice these less serious side effects, talk with your doctor:

• Dizziness
• Joint pain
• Mild nausea, vomiting, stomach upset

If you notice other side effects that you think are caused by this medicine, tell your doctor

Call your doctor for medical advice about side effects. You may report side effects to FDA at 1-800-FDA-1088

Last Updated: 9/6/2024