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Methimazole is available as a 5 mg and 10 mg oral tablet.

Methimazole is an antithyroid agent that is used to treat high thyroid hormone levels (hyperthyroidism) in people:
With Graves’ disease or other medical conditions who can’t receive thyroid surgery or radioactive iodine treatment
Who are preparing to undergo thyroid surgery or radioactive iodine treatment

Methimazole belongs to a class of medications called antithyroids. It works by blocking the thyroid gland from making thyroid hormones. Thyroid hormones help regulate your body temperature, control how your body uses energy, and keep your organ systems working well. But having too much thyroid hormone in your body can cause unpleasant symptoms, including weight loss, irregular heartbeat, frequent bowel movements, an enlarged thyroid gland, and feeling hot when others don’t. By blocking your thyroid from making these hormones, Methimazole helps to bring your thyroid hormone levels down to a healthy level. This will help relieve your symptoms and give you more energy throughout the day.

Your dose depends on whether you’re starting or continuing therapy. Your provider will adjust your continuing dose throughout treatment based on your thyroid hormone levels.
Adults: The typical starting dose ranges from 15 mg to 60 mg per day, depending on how severe your hyperthyroidism is. The total daily dose is split into 3 smaller doses that are taken by mouth every 8 hours. Once your thyroid hormone levels become normal, you’ll continue treatment at a maintenance dose that typically ranges from 5 mg to 15 mg taken once a day. Children: The dose will depend on your child’s body weight. The typical starting dose is 0.4 mg/kg of body weight per day. This total dose is split into 3 smaller doses given by mouth every 8 hours. The typical maintenance dose is about half of the starting dose.

Methimazole is a safe and effective treatment when used for FDA licensed indications. However, like all medications, they may give you unwanted side effects. You should always discuss potential side effects with your physician to ensure the medication is suitable and right for you.

Common side effects of Methimazole:

• Raised, itchy rash
• Nausea
• Vomiting
• Stomach upset
• Loss of taste
• Unusual hair loss
• Drowsiness

Serious side effects are rare with Methimazole. Contact your healthcare provider immediately if you experience any of the following.

• Low white blood cells (agranulocytosis): fever, fatigue, chills, sore throat
• Inflamed blood vessels (vasculitis): rash, nerve pain, chest pain, stomach pain
• Unusual bleeding or bruising: black stools, blood in urine, bleeding or bruising that doesn’t go away
• Liver problems: upper right stomach pain, loss of appetite, yellowing of skin or whites of eyes (jaundice)

The following medications may interact with Methimazole:

• Anticoagulants (oral):
• Due to potential inhibition of vitamin K activity by Methimazole, the activity of oral anticoagulants (e.g., warfarin) may be increased; additional monitoring of PT/INR should be considered, especially before surgical procedures
• β-adrenergic blocking agents:
• Hyperthyroidism may cause an increased clearance of beta blockers with a high extraction ratio. A dose reduction of beta-adrenergic blockers may be needed when a hyperthyroid patient becomes euthyroid
• Digitalis glycosides
• Serum digitalis levels may be increased when hyperthyroid patients on a stable digitalis glycoside regimen become euthyroid; a reduced dosage of digitalis glycosides may be needed
• Theophylline: Theophylline clearance may decrease when hyperthyroid patients on a stable theophylline regimen become euthyroid; a reduced dose of theophylline may be needed

Various FDA-approved generic manufacturers

Because of the risk for congenital malformations associated with use of Methimazole in the first trimester of pregnancy, it may be appropriate to use other agents in pregnant women requiring treatment for hyperthyroidism. If Methimazole is used, the lowest possible dose to control the maternal disease should be given.

• Tapazole