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Methimazole is an oral antithyroid tablet used to treat hyperthyroidism, including Graves' disease and toxic multinodular goiter. It works by blocking the thyroid gland from making new thyroid hormone, helping to bring hormone levels back to normal.
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Dr. Steve Malen, PharmD
Dr. Steven Blikstein, PharmD
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Methimazole is a thionamide antithyroid medication used to treat hyperthyroidism caused by Graves' disease or toxic multinodular goiter. It is also used to control thyroid levels before thyroid surgery or radioactive iodine therapy. Methimazole works by inhibiting thyroid peroxidase, the enzyme the thyroid gland uses to produce thyroxine (T4) and triiodothyronine (T3). Initial doses typically range from 15 to 60 mg per day depending on severity, with maintenance doses of 5 to 15 mg per day, often taken once daily. Common side effects include rash, itching, nausea, joint pain, and changes in taste. Rare but serious side effects include agranulocytosis (a sharp drop in white blood cells) and liver injury, so patients should contact their doctor right away if they develop fever, sore throat, unusual bruising, yellowing of the skin or eyes, or dark urine. Regular blood tests are used to monitor thyroid levels and adjust the dose. Methimazole is sold under the brand name Tapazole.
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Methimazole is used to treat hyperthyroidism from Graves' disease or toxic multinodular goiter, and to prepare patients for thyroid surgery or radioactive iodine therapy. Treatment usually starts at 15 to 60 mg per day depending on severity, then is lowered to a maintenance dose of 5 to 15 mg once daily once thyroid levels normalize. Your doctor will check thyroid blood tests every few weeks at first to adjust the dose.
Common side effects include rash, itching, hives, nausea, upset stomach, joint pain, headache, and a change in taste.
Important safety warning: Methimazole can rarely cause agranulocytosis, a serious drop in white blood cells that lowers the body's ability to fight infection. Stop taking methimazole and contact your doctor right away if you develop fever, sore throat, mouth sores, or other signs of infection. Liver injury has also been reported; seek medical care for yellowing of the skin or eyes, dark urine, pale stools, or pain in the upper right abdomen.
Methimazole can harm an unborn baby when used in the first trimester of pregnancy. Tell your doctor if you are pregnant or planning a pregnancy, as propylthiouracil may be preferred early in pregnancy. Methimazole may also change how blood thinners such as warfarin, beta blockers, digoxin, and theophylline work, so share a full list of your medications with your doctor and pharmacist.
Thyroid Disorder Treatment
Yes. Methimazole (Tapazole) is the most commonly prescribed antithyroid medication and the first-choice drug treatment for most people with hyperthyroidism, including Graves' disease and toxic nodular goiter. Other thyroid disorder treatments include radioactive iodine and thyroid surgery, and your provider will help you choose the right approach.
Methimazole treats hyperthyroidism, an overactive thyroid that makes too much hormone. It is not used for hypothyroidism, an underactive thyroid, which is treated with thyroid hormone replacement such as levothyroxine. If methimazole lowers your levels too far, you can develop hypothyroidism, so regular blood tests are important.
Methimazole can ease symptoms of an overactive thyroid, such as a racing or irregular heartbeat, shakiness, anxiety, trouble sleeping, unexplained weight loss, sweating, and heat intolerance. Thyroid eye symptoms from Graves' disease, like bulging, dry, or irritated eyes, may need separate care from an eye specialist.
Thyroid disorders are diagnosed and monitored with blood tests for TSH, free T4, and sometimes T3. Antibody tests can confirm Graves' disease. While on methimazole, these tests are usually repeated every 4 to 6 weeks at first so your provider can adjust your dose.
Thyroid disorders, including Graves' disease, often run in families. Having a parent or sibling with an autoimmune thyroid disorder raises your risk, but it does not change how methimazole works. If thyroid disease runs in your family, mention it to your provider so symptoms can be checked early.
Administration & Dosage
Methimazole is usually taken by mouth once a day, with or without food. Some people take higher doses split into two or three doses at first. Take it at the same time each day and do not stop unless your provider tells you to.
Starting doses usually range from 5 to 30 mg per day depending on how overactive the thyroid is. Once thyroid levels return to normal, many people take a lower maintenance dose of 5 to 10 mg per day. Methimazole comes in 5 mg and 10 mg tablets.
Many people notice improvement within a few weeks, but thyroid levels usually take about 4 to 8 weeks to return to normal. Treatment for Graves' disease often continues for 12 to 18 months.
Uses & Mechanism of Action
Methimazole is a prescription antithyroid medication, sold under the brand name Tapazole. It is used to treat hyperthyroidism and to prepare people for thyroid surgery or radioactive iodine treatment.
Methimazole blocks the thyroid gland from using iodine to make thyroid hormone. This lowers the amount of hormone in your blood over several weeks. It does not destroy the thyroid, so its effects wear off if you stop taking it.
No. Methimazole is not a controlled substance. It is a standard prescription medication that can be refilled as directed by your prescriber.
Side Effects & Safety
Common side effects include rash, itching, hives, joint pain, nausea, upset stomach, headache, and a change in taste. Tell your provider if these are bothersome or do not go away.
Methimazole can rarely cause agranulocytosis, a serious drop in white blood cells that makes it hard to fight infection. It is most likely in the first few months. Call your provider right away if you develop a fever, sore throat, mouth sores, or other signs of infection.
Yes. If the dose is higher than you need, thyroid hormone levels can drop too low. Symptoms of hypothyroidism include fatigue, weight gain, feeling cold, dry skin, and constipation. Regular blood tests help keep your dose in the right range.
Methimazole can cause birth defects when taken during the first trimester, so PTU is usually preferred early in pregnancy. Many providers switch back to methimazole in the second trimester. If you are pregnant or planning a pregnancy, talk to your provider before making any change.
Interactions & Contraindications
Methimazole can change how warfarin works and may affect your risk of bleeding. If you take warfarin, your provider may check your INR more often when starting or changing your methimazole dose.
Possibly. As hyperthyroidism improves, doses of medications such as beta blockers, digoxin, and theophylline may need to be lowered. Tell your provider about all medications and supplements you take.
People who have had a serious allergic reaction to methimazole should not take it. It is generally avoided in the first trimester of pregnancy and used with caution in people with liver problems or a history of low white blood cell counts.
Generic & Alternatives
Yes. Methimazole is the generic version of Tapazole. It contains the same active ingredient and works the same way as the brand name.
Both are antithyroid medications for hyperthyroidism. Methimazole is taken once daily and has a lower risk of serious liver injury, so it is usually the first choice. PTU is taken every 8 hours and is mainly used in the first trimester of pregnancy, in thyroid storm, or when methimazole is not tolerated.