Methimazole
Methimazole (meth IM a zole) is a generic medication prescribed for certain adults and children with an overactive thyroid. Methimazole belongs to a group of drugs called antithyroid medications.
Medically reviewed by Alex Brewer, PharmD, MBA on May 30, 2023
Written by Jennifer Mitri Williamson, PharmD
This article describes methimazole’s uses, side effects, and more. Below you’ll also find some coupon options to help save on the cost of methimazole.
Side effects of methimazole
Methimazole may cause mild or serious side effects (also known as adverse effects). More common mild side effects of methimazole and its serious side effects are listed below. This article doesn’t include all possible side effects of the drug. Side effects can vary based on your age, overall health, and any other medications you take.
To learn more about methimazole’s side effects, ask your doctor or pharmacist. You can also read the prescribing information* for methimazole.
* To view methimazole’s prescribing information, see the “Article resources” section below.
Mild side effects
More common mild side effects reported with methimazole are listed below.
This article doesn’t include all possible mild side effects of the drug. To learn more about methimazole’s side effects, see the prescribing information* for methimazole.
With many drugs, mild side effects may go away within a few days or a couple of weeks. If the side effects are bothersome, tell your doctor or pharmacist. They may be able to suggest ways to manage them.
Methimazole oral tablet’s mild side effects include:
- skin rash
- nausea, vomiting, or both
- joint pain
- itchiness
- mild allergic reaction†
* To view methimazole’s prescribing information, see the “Article resources” section below.
† For details about this side effect, see the “Interactions and warnings for methimazole” section below.
Serious side effects
Serious side effects of methimazole are listed below.
This article doesn’t include all possible serious side effects of the drug. To learn more about methimazole’s side effects, see the prescribing information* for methimazole.
With many drugs, serious side effects are possible but not common. If you have serious side effects from this drug, call your doctor right away. If you’re having severe symptoms or a medical emergency, call 911 or a local emergency number.
In general, methimazole’s serious side effects include:
- decreased blood cell levels, including low levels of platelets and red blood cells
- liver problems, including hepatitis (inflammation of the liver)
- kidney problems
- inflammation (swelling) of the blood vessels, such as vasculitis or periarteritis
- low level of prothrombin (a protein involved in blood clotting), which may cause bleeding that lasts longer than usual
- insulin autoimmune syndrome (an immune system reaction to the insulin your body produces, leading to low blood sugar)
- lupus-like syndrome (an immune system reaction that causes similar symptoms to lupus)
- drug fever (a fever that occurs when you take certain medications)
- low thyroid activity
- severe allergic reaction†
* To view methimazole’s prescribing information, see the “Article resources” section below.
† For details about this side effect, see the “Interactions and warnings for methimazole” section below.
Common questions about methimazole
Below you’ll find answers to a few commonly asked questions about methimazole.
Can methimazole be used in cats?
Yes, but it’s not the same as methimazole that’s used in humans. The human form of methimazole is different from the form used in cats.
Methimazole for cats is available as generic methimazole. It’s also available as the brand-name drug Felimazole.
Talk with your veterinarian to learn more about treatments for overactive thyroid in cats, including the forms of methimazole approved for this use.
How does methimazole compare with carbimazole or thiamazole?
Like methimazole, carbimazole is used to treat an overactive thyroid. However, carbimazole isn’t approved for use in the United States. It’s approved for use in other countries, including Australia and many European countries.
Methimazole is also called thiamazole. So they are the same medication and have the same side effects and dosages.
There are other options in addition to methimazole for overactive thyroid. They include propylthiouracil (PTU), iodine therapy, or surgery.
If you have questions about the best treatment option for your condition, talk with your doctor or pharmacist. They can help determine the best treatment option for you.
Will I experience certain side effects when stopping methimazole?
It’s possible for you to experience side effects when stopping methimazole. Methimazole is used to treat an overactive thyroid. So, the drug works by slowing down the amount of thyroid hormone that your body makes.
If you stop taking methimazole, your thyroid may become overactive again. This means that your body may begin to produce too much thyroid hormone again. So if you stop taking methimazole, you may experience symptoms of overactive thyroid. Symptoms may include:
- weight loss
- anxiety
- panic attacks
- hair loss
- fast heart rate
If you’d like to stop taking methimazole, talk with your doctor. They can recommend how and when to stop treatment with methimazole. Also, they may recommend a different treatment option for your condition.
What is the best time of day to take methimazole?
Methimazole is usually taken three times per day, separated by about 8 hours per dose. For example, if you take your first dose at 7 a.m., you will take your second dose at 3 p.m. and your last dose at 11 p.m.
Before you start taking methimazole, your doctor or pharmacist will discuss the best times to take your medication.
Is weight gain a side effect of methimazole?
No, weight gain wasn’t a side effect that people taking methimazole reported in studies. However, having an overactive thyroid may cause you to lose weight. So if you have treatment for your overactive thyroid, you may gain some weight.
If you notice weight gain that’s bothersome, talk with your doctor. They can help recommend the best ways to manage your weight.
How does methimazole work? And how long does it take to start working?
Methimazole works to treat an overactive thyroid in certain adults and children. It works by slowing down the amount of thyroid hormones that your body makes.
The drug begins working as soon as you take your first dose.
If you have more questions about how methimazole works or when it should start working, talk with your doctor or pharmacist.
Dosage of methimazole
The dosage of methimazole your doctor prescribes may vary based on your condition and certain other factors. Talk with your doctor about the dosage you should follow.
Taking methimazole
Methimazole oral tablet is swallowed. The manufacturer of this medication doesn’t specify whether the drug should be taken with or without food. If you have questions about how to take methimazole, talk with your doctor or pharmacist.
Your doctor will talk with you about how to take methimazole. They’ll explain how much to take and how often. Always follow your doctor’s recommendation.
See the “Common questions about methimazole” section for information on missed doses and the best time to take this drug.
Overdose of methimazole
You should not take more methimazole than your doctor prescribes. For some drugs, doing so may lead to serious side effects or overdose.
If you think you’ve taken too much methimazole, call your doctor or pharmacist right away. Or you could call 800-222-1222 to speak with someone at America’s Poison Centers. You can also use its online resource. If you have concerning symptoms, call 911 or a local emergency number immediately. You can also go to the closest emergency room.
Uses of methimazole
The Food and Drug Administration (FDA) approves prescription drugs such as methimazole for certain conditions. Approved uses for methimazole are described below.
Use for hyperthyroidism
Doctors may prescribe methimazole oral tablet for treating hyperthyroidism (overactive thyroid). It’s used for this purpose in certain adults and children. Methimazole may be a short-term or a long-term treatment option.
Specifically, methimazole may be used in people with Graves’ disease with overactive thyroid or goiter who cannot have surgery or iodine therapy. (Graves’ disease is an autoimmune condition that causes an overactive thyroid. Goiter is a condition that increases the size of your thyroid gland.) In this case, the drug may be used as a long-term treatment option.
Methimazole may also be used in people with overactive thyroid that are getting ready for thyroid surgery or iodine therapy. In this case, the drug may be used as a short-term treatment option.
With an overactive thyroid, your thyroid gland makes too much thyroid hormone. This may cause symptoms such as:
- weight loss
- fast heart rate
- anxiety
- sweating
- goiter
Interactions and warnings for methimazole
Below, you’ll find information about methimazole’s possible interactions and warnings.
Interactions of methimazole
Certain things may affect how a drug works. These include getting vaccines, consuming alcohol or certain foods, or taking the drug with other medications. This effect is called a drug interaction.
Before you take methimazole, ask your doctor to check for possible interactions. Be sure to tell them about any of the following you take or use:
- prescription drugs
- over-the-counter medications
- vitamins, herbs, or supplements
To learn about drug-condition interactions, see the “Warnings for methimazole” section below.
Warnings for methimazole
Some people should not take methimazole, and others should take it cautiously.
Methimazole could cause harm to people with certain health conditions. This effect is called a drug-condition interaction. Other factors can also affect whether methimazole is a safe option for you. These warnings may differ based on the form of methimazole you take.
Ask your doctor about specific warnings for methimazole, and be sure to tell your doctor about your:
- current health, including any allergies to medications
- past health conditions or surgeries
Allergic reaction
Methimazole can cause an allergic reaction in some people. Severe allergic reactions are rare but possible.
If you’ve had an allergic reaction to methimazole or any of its ingredients, your doctor will likely not prescribe methimazole. They can tell you about medications that are safer options for you.
A mild allergic reaction may cause the following symptoms:
A severe allergic reaction may cause the following symptoms:
- swelling under your skin, usually in your hands, feet, eyelids, or lips
- swelling of your mouth, throat, or tongue, which can cause breathing problems
If you have an allergic reaction to methimazole, call your doctor right away. If you have severe symptoms, call 911 or a local emergency number.
Pregnancy or breastfeeding and methimazole
Information about methimazole and pregnancy and breastfeeding is described below.
Methimazole and pregnancy
There are risks to taking methimazole during pregnancy. But there are also risks with having an untreated thyroid condition while pregnant. (Keep in mind that methimazole is used for treating an overactive thyroid.)
If you’re planning a pregnancy or can become pregnant, talk with your doctor about overactive thyroid treatment options during pregnancy. Together, you can discuss the risks and benefits of your treatment options and decide whether you should take methimazole during pregnancy.
Methimazole and breastfeeding
It’s not known for sure whether methimazole should be taken while breastfeeding. The drug passes into breast milk, but it doesn’t seem to cause problems in children who are breastfed. If you’re currently breastfeeding or planning to do so, talk with your doctor before taking this medication.
Methimazole coupon
You may be able to save money on your prescription for methimazole by using our Perks discount coupons. They can be found at the end of this article.
If you have questions about how to pay for methimazole, talk with your doctor or pharmacist.
Note: Optum Perks coupons cannot be used with insurance copays or benefits.
What to ask your doctor
This article describes methimazole’s uses and dosage, ways to save on cost, and more. Let your doctor know if you have questions about methimazole or would like more details about it.
Here’s a list of some possible questions you may want to ask your doctor:
- Is methimazole available as a brand-name drug?
- What other treatment options are available if I can’t afford methimazole?
- If I experience side effects from this medication, will you decrease my dose?
Article resources
- Food and Drug Administration. (2023). Orange Book: Approved drug products with therapeutic equivalence evaluations. https://www.accessdata.fda.gov/scripts/cder/ob/index.cfm
- Hyperthyroidism in cats—There’s an FDA-approved drug to treat it. (2019). https://www.fda.gov/animal-veterinary/animal-health-literacy/hyperthyroidism-cats-theres-fda-approved-drug-treat-it
- Methimazole tablets, USP. (2023). https://nctr-crs.fda.gov/fdalabel/services/spl/set-ids/c511344b-cc7f-499b-bb21-5b2312ff311e/spl-doc
Disclaimer: Optum Perks has made every effort to make certain that all information is factually correct, comprehensive, and up to date. However, this article should not be used as a substitute for the knowledge and expertise of a licensed healthcare professional. You should always consult your doctor or another healthcare professional before taking any medication. The drug information contained herein is subject to change and is not intended to cover all possible uses, directions, precautions, warnings, drug interactions, allergic reactions, or adverse effects. The absence of warnings or other information for a given drug does not indicate that the drug or drug combination is safe, effective, or appropriate for all patients or all specific uses.
- Generic
- Tablet
- 5mg
- 30 Tablets
Dosage settings
Name
Methimazole
Pronunciation
(meth IM a zole)
Brand Names: US
Tapazole
What is this drug used for?
It is used to treat an overactive thyroid gland.
What do I need to tell my doctor BEFORE I take this drug?
If you are allergic to this drug; any part of this drug; or any other drugs, foods, or substances. Tell your doctor about the allergy and what signs you had. This drug may interact with other drugs or health problems. Tell your doctor and pharmacist about all of your drugs (prescription or OTC, natural products, vitamins) and health problems. You must check to make sure that it is safe for you to take this drug with all of your drugs and health problems. Do not start, stop, or change the dose of any drug without checking with your doctor.
What are some things I need to know or do while I take this drug?
Tell all of your health care providers that you take this drug. This includes your doctors, nurses, pharmacists, and dentists. Have blood work checked as you have been told by the doctor. Talk with the doctor. Some blood vessel problems have happened with this drug. Sometimes, this has led to severe health problems like kidney problems, nerve problems, and bleeding in the lungs. If you have questions, talk with the doctor. This drug may cause harm to the unborn baby if you take it while you are pregnant, especially in the first trimester. If you are pregnant or you get pregnant while taking this drug, call your doctor right away. Tell your doctor if you are breast-feeding. You will need to talk about any risks to your baby. Have your baby's thyroid checked if you are using this drug and breast-feeding.
What are some side effects that I need to call my doctor about right away?
WARNING/CAUTION: Even though it may be rare, some people may have very bad and sometimes deadly side effects when taking a drug. Tell your doctor or get medical help right away if you have any of the following signs or symptoms that may be related to a very bad side effect: Signs of an allergic reaction, like rash; hives; itching; red, swollen, blistered, or peeling skin with or without fever; wheezing; tightness in the chest or throat; trouble breathing, swallowing, or talking; unusual hoarseness; or swelling of the mouth, face, lips, tongue, or throat. Signs of liver problems like dark urine, feeling tired, not hungry, upset stomach or stomach pain, light-colored stools, throwing up, or yellow skin or eyes. Signs of kidney problems like unable to pass urine, change in how much urine is passed, blood in the urine, or a big weight gain. Signs of lupus like a rash on the cheeks or other body parts, sunburn easy, muscle or joint pain, chest pain or shortness of breath, or swelling in the arms or legs. Signs of low blood sugar like dizziness, headache, feeling sleepy, feeling weak, shaking, a fast heartbeat, confusion, hunger, or sweating. Shortness of breath. Coughing up blood. Swelling. A burning, numbness, or tingling feeling that is not normal. Swollen gland. Low blood cell counts have happened with this drug. If blood cell counts get very low, this can lead to bleeding problems, infections, or anemia. Call your doctor right away if you have signs of infection like fever, chills, or sore throat; any unexplained bruising or bleeding; or if you feel very tired or weak.
What are some other side effects of this drug?
All drugs may cause side effects. However, many people have no side effects or only have minor side effects. Call your doctor or get medical help if any of these side effects or any other side effects bother you or do not go away: Itching. Change in taste. Feeling sleepy. Headache. Muscle or joint pain. Hair loss. Upset stomach or throwing up. Stomach pain. Change in color of skin. These are not all of the side effects that may occur. If you have questions about side effects, call your doctor. Call your doctor for medical advice about side effects. You may report side effects to the FDA at 1-800-332-1088. You may also report side effects at https://www.fda.gov/medwatch.
How is this drug best taken?
Use this drug as ordered by your doctor. Read all information given to you. Follow all instructions closely. Keep taking this drug as you have been told by your doctor or other health care provider, even if you feel well.
What do I do if I miss a dose?
Take a missed dose as soon as you think about it. If it is close to the time for your next dose, skip the missed dose and go back to your normal time. Do not take 2 doses at the same time or extra doses.
How do I store and/or throw out this drug?
Store at room temperature in a dry place. Do not store in a bathroom. Keep all drugs in a safe place. Keep all drugs out of the reach of children and pets. Throw away unused or expired drugs. Do not flush down a toilet or pour down a drain unless you are told to do so. Check with your pharmacist if you have questions about the best way to throw out drugs. There may be drug take-back programs in your area.
General drug facts
If your symptoms or health problems do not get better or if they become worse, call your doctor. Do not share your drugs with others and do not take anyone else's drugs. Some drugs may have another patient information leaflet. Check with your pharmacist. If you have any questions about this drug, please talk with your doctor, nurse, pharmacist, or other health care provider. If you think there has been an overdose, call your poison control center or get medical care right away. Be ready to tell or show what was taken, how much, and when it happened.
Consumer Information Use and Disclaimer
This information should not be used to decide whether or not to take this medicine or any other medicine. Only the healthcare provider has the knowledge and training to decide which medicines are right for a specific patient. This information does not endorse any medicine as safe, effective, or approved for treating any patient or health condition. This is only a brief summary of general information about this medicine. It does NOT include all information about the possible uses, directions, warnings, precautions, interactions, adverse effects, or risks that may apply to this medicine. This information is not specific medical advice and does not replace information you receive from the healthcare provider. You must talk with the healthcare provider for complete information about the risks and benefits of using this medicine.