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Methimazole

Brand names: Tapazole

Methimazole lowers the amount of thyroid hormone the thyroid makes. It treats an overactive thyroid, such as Graves' disease.

Brand namesTapazole
Type of medicineAntithyroid medicine
Prescription?Prescription
ImportantThis page is general information, not a prescription. Don't start, stop, or change a medicine without talking to your provider or pharmacist.

Overview

It takes several weeks to bring hormone levels down. Blood tests guide the dose.

What it's used for

  • Overactive thyroid (hyperthyroidism), including Graves' disease
  • Preparing for thyroid surgery or radioactive iodine

How to take it

  • Take it the same way each day, with or without food.
  • Keep all blood test appointments.

Your dose depends on your health and other medicines. Always follow your prescription label, and ask your pharmacist if anything is unclear.

Side effects

Common side effects

  • Rash or itching
  • Joint pain
  • Nausea
  • Change in taste
Call 911Fever, sore throat, or mouth sores. Stop it and get a blood count the same day (rare but serious drop in white blood cells).
Call your provider todayYellow skin or eyes, dark urine, or upper right belly pain
Call your provider todayFeeling cold, tired, and gaining weight (dose may be too high)

Warnings

  • Low white blood cells can happen suddenly; report infections right away.

Other medicines, foods, and alcohol

  • It can change how warfarin works.
  • Beta blocker and digoxin doses may need changing as thyroid levels fall.

Tell your provider and pharmacist about every medicine, vitamin, and supplement you take.

Pregnancy and breastfeeding

Propylthiouracil is often used in the first trimester instead. Talk with your provider before pregnancy.

Missed doses, overdose, and storage

If you miss a dose

Take it as soon as you remember, unless it's almost time for your next dose. Then skip the missed dose. Don't take two doses at once.

If someone takes too much

Call Poison Control at 1-800-222-1222 or get help online at poison.org. Call 911 if the person collapses, has a seizure, has trouble breathing, or can't be woken.

Storing it

Store at room temperature, away from heat and moisture (not in the bathroom), and out of reach of children and pets.

Conditions it's used for

Sources

Last updated 2026-11-13.