Uses
What is methimazole used for?
Methimazole is commonly used to treat people with Graves' disease or toxic multinodular goiter who have an overactive thyroid (hyperthyroidism).
Methimazole can also be used to help reduce symptoms of an overactive thyroid before having surgery to remove the thyroid or radioactive iodine therapy.
Methimazole may also be used for other conditions as determined by your healthcare provider.
How does methimazole work (mechanism of action)?
Methimazole works by blocking your body from making too much thyroid hormone.
How is methimazole supplied (dosage forms)?
Methimazole is available in the following dosage forms that are taken by mouth.
- 5 mg oral tablets
- 10 mg oral tablets
How should I store methimazole?
Methimazole should be stored at room temperature, between 68 F to 77 F (20 C to 25 C). It can be exposed to temperatures between 59 F to 86 F (15 C to 30 C) for shorter periods of time, such as when transporting it. Store in a cool, dry place. Protect from light.
Side Effects
What are the most common side effects of methimazole?
The most common side effects of methimazole are listed below. Tell your healthcare provider if you have any of these side effects that bother you.
- Skin rash, hives, or discoloration
- Nausea or vomiting
- Upper stomach pain or tenderness
- Joint, muscle, or nerve pain
- Loss of taste
- Hair loss
- Headache or dizziness
- Itching
- Sleepiness
- Fluid retention (edema)
- Skin or the whites of your eyes turning yellowish in color (also called jaundice)
- Enlarged salivary glands or lymph nodes
There may be other side effects of methimazole that are not listed here. Contact your healthcare provider if you think you are having a side effect of a medicine. In the U.S., you can report side effects to the FDA at www.fda.gov/medwatch or by calling 800-FDA-1088. In Canada, you can report side effects to Health Canada at www.health.gc.ca/medeffect or by calling 866-234-2345.
What are the serious side effects of methimazole?
While less common, the most serious side effects of methimazole are described below, along with what to do if they happen.
Severe Allergic Reactions. Methimazole may cause allergic reactions, which can be serious. Stop taking methimazole and get help right away if you have any of the following symptoms of a serious allergic reaction.
- Breathing problems or wheezing
- Racing heart
- Fever or general ill feeling
- Swollen lymph nodes
- Swelling of the face, lips, mouth, tongue, or throat
- Trouble swallowing or throat tightness
- Itching, skin rash, or pale red bumps on the skin called hives
- Nausea or vomiting
- Dizziness, feeling lightheaded, or fainting
- Stomach cramps
- Joint pain
Blood Disorders. Methimazole can cause blood disorders, such as agranulocytosis, aplastic anemia, low platelet levels (thrombocytopenia), and low white blood cell levels (leukopenia). Stop taking methimazole and get help right away if you have any of the following symptoms of blood disorders.
- Fever, chills or sore throat
- Shortness of breath
- Pale or yellowish skin
- Easy bruising or bleeding
- Frequent infection
- Unusual weakness or tiredness
- Dizziness, lightheadedness, or feeling like you are about to pass out
- Headache
- Fast or abnormal heartbeat
Liver Damage. Liver damage, also called hepatotoxicity, can happen when taking methimazole. Stop taking methimazole and call your healthcare provider right away if you have any of the following symptoms of liver damage.
- Nausea or vomiting
- Stomach or belly pain
- Fever
- Weakness or unusual tiredness
- Itching
- Loss of appetite
- Light-colored poop
- Dark-colored urine
- Your skin or the whites of your eyes turning yellowish in color (also called jaundice)
Swelling of Blood Vessels (Vasculitis). Methimazole can cause inflammation and swelling of your small blood vessels in your skin, kidneys, or lungs. Call your healthcare provider right away if you develop any of the following symptoms.
- Skin turning red or purple
- Rash
- Painful skin or swelling
- Pink, red, brown or foamy urine (pee)
- Reduced amount of pee
- Shortness of breath or coughing up blood
Low Thyroid Levels (Hypothyroidism). Methimazole can cause the function of your thyroid gland to change, which can lead to low thyroid levels. Keep all appointments to have your blood checked. Tell your healthcare provider if you have any of the following signs of low thyroid hormones.
- Weight gain
- Feeling cold
- Tiredness that does not go away or continues to worsen
- Constipation
Immune System Reactions. Methimazole can cause inflammation of your liver, blood vessels, or lymph vessels and cause symptoms that look like a condition called lupus. Stop taking methimazole and call your healthcare provider right away if you develop any of the following symptoms.
- Rash
- Joint pain
- Fever
- Weakness or unusual tiredness
Low Blood Sugar (Hypoglycemia). Methimazole can cause low blood sugar, which can be serious and may lead to death. Do not take methimazole and call your healthcare provider right away if you have any of the following symptoms of hypoglycemia.
- Headache
- Crankiness or anxiety
- Hunger
- Dizziness or confusion
- Blurry vision
- Slurred speech
- Sweating
- Feeling jittery or shakiness
- Fast heartbeat
- Seizures
Warnings & Precautions
Who should not use methimazole?
Allergies to Ingredients. People who are allergic to any of the following should not take methimazole.
- Methimazole
- Tapazole
- Any of the ingredients in the specific product dispensed
Your pharmacist can tell you all of the ingredients in the specific methimazole products they stock.
What should I know about methimazole before using it?
Do not take methimazole unless it has been prescribed to you by a healthcare provider. Take it as prescribed.
Do not share methimazole with other people, even if they have the same condition as you. It may harm them.
Keep methimazole out of the reach of children.
It is important to keep all of your healthcare appointments while you are taking methimazole, including lab appointments. These lab tests help your healthcare provider know if the medicine is working.
What should I tell my healthcare provider before using methimazole?
Tell your healthcare provider about all of your health conditions and any prescription or over-the-counter (OTC) medicines, vitamins/minerals, herbal products, and other supplements you are using. This will help them determine if methimazole is right for you.
In particular, make sure that you discuss any of the following.
Other Medicines and Supplements. Methimazole may interact with other medicines and supplements. Before taking methimazole, tell your healthcare provider about any prescription or over-the-counter (OTC) medicines, vitamins/minerals, herbal products, and other supplements you are using. See the Interactions section for more details
Pregnancy. Methimazole can cause harm to an unborn baby. Tell your healthcare provider if you are or plan to become pregnant.
Breastfeeding. Methimazole passes into breast milk. Tell your healthcare provider if you are breastfeeding or plan to breastfeed. Your healthcare provider will advise you if you should take methimazole while breastfeeding.
Interactions
Does methimazole interact with foods or drinks?
There are no known interactions between methimazole and foods or drinks.
It is unknown if drinking alcohol will affect methimazole.
Does methimazole interact with other medicines (drug interactions)?
Methimazole may interact with certain medicines. Always tell your healthcare provider about any prescription or over-the-counter (OTC) medicines, vitamins/minerals, herbal products, and other supplements you are using.
In particular, make sure that you discuss if you are using any of the following before taking methimazole.
- Warfarin , which is a blood thinner
- A beta-blocker, such as metoprolol (Lopressor, Toprol XL, and others), atenolol (Tenormin), or propranolol (Inderal LA, Innopran XL), which is a medicine that may be used for certain heart conditions or to reduce blood pressure
- Digoxin (Lanoxin), which is a medicine used to treat irregular heartbeat and some types of heart failure
- Theophylline (Theo-24), which is a medicine used for asthma or other chronic lung conditions
This may not be a complete list of medicines that can interact with methimazole. Always check with your healthcare provider.
Overdose/Missed Dose
What should I do if I accidentally use too much methimazole?
If you or someone else has used too much methimazole, get medical help right away, call 911, or contact a Poison Control center at 800-222-1222.
What should I do if I miss a dose of methimazole?
If you miss a dose, take it as soon as you remember. If it is almost time for your next dose, skip the missed dose and only take the next dose. Do not take double or extra doses.
Are you currently using Methimazole?
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