Methimazole: Uses & Side Effects

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.

How should I take methimazole?

Follow all directions on your prescription label. Your doctor may occasionally change your dose. Do not use methimazole in larger or smaller amounts or for longer than recommended.

Methimazole is usually taken every 8 hours. Take your doses at regular intervals to keep a steady amount of the drug in your body at all times.

If a child is using this medicine, tell your doctor if the child has any changes in weight. Methimazole doses are based on weight in children, and any changes may affect your child’s dose.

Methimazole can lower blood cells that help your body fight infections and help your blood to clot. 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.

Use methimazole regularly to get the most benefit, even if you feel fine or have no symptoms of hyperthyroidism. Get your prescription refilled before you run out of medicine completely.

If you need surgery, tell the surgeon ahead of time that you are using methimazole.

Store at room temperature away from moisture and heat.

Precautions

You should not use methimazole if you are allergic to it, or if you are pregnant or breast-feeding.

To make sure methimazole is safe for you, tell your doctor if you have:

  • liver disease;
  • a blood cell disorder;
  • a weak immune system.

Using methimazole during pregnancy could harm the unborn baby. Tell your doctor if you are pregnant or if you become pregnant while using this medicine.

Methimazole can pass into breast milk and may harm a nursing baby. You should not breast-feed while using this medicine.

Do not give this medicine to a child without medical advice.

Side Effects

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

Serious and sometimes fatal infections may occur during treatment with methimazole. Stop using methimazole and call your doctor right away if you have signs of infection such as:

sudden weakness or ill feeling, fever, chills, sore throat, cold or flu symptoms;

painful mouth sores, pain when swallowing, red or swollen gums; or

pale skin, easy bruising, unusual bleeding.

Call your doctor at once if you have:

  • swollen glands in your neck or jaw; or
  • liver problems–nausea, upper stomach pain, itching, tiredness, loss of appetite, dark urine, clay-colored stools, jaundice (yellowing of the skin or eyes).

Common side effects may include:

  • nausea, vomiting, upset stomach;
  • headache, dizziness, drowsiness;
  • numbness or tingly feeling;
  • rash, itching, skin discoloration;
  • muscle or joint pain;
  • hair loss;
  • decreased sense of taste.

Interactions

Tell your doctor about all your current medicines and any you start or stop using, especially:

  • digoxin, digitalis, theophylline;
  • a blood thinner–warfarin, Coumadin, Jantoven;
  • a beta blocker–atenolol, carvedilol, labetalol, metoprolol, nadolol, propranolol, sotalol, and others.

Always consult your healthcare provider to ensure the information displayed on this page applies to your personal circumstances.

Keywords: methimazole; hyperthyroidism.

* The Content is not intended to be a substitute for professional medical advice, diagnosis, or treatment. Always seek the advice of your physician or other qualified health provider with any questions you may have regarding a medical condition.
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