This article describes possible side effects of methimazole oral tablet. You can explore this overview article to learn more about methimazole, including the drug’s uses, side effects, ways to save on cost, and more.
Methimazole oral tablet is a generic medication. It isn’t available in a brand-name version.
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More common side effects of methimazole
Methimazole oral tablet may cause mild or serious side effects. Below are some of the more common side effects of this medication.
Commonly reported side effects of methimazole oral tablet include:
- unusual sensations, such as tingling or pins-and-needles feeling
- headache
- joint pain
- nausea or vomiting
- upper belly pain or discomfort
Mild side effects of methimazole
Methimazole may cause certain mild side effects. Usually, mild side effects are temporary and can be easily managed. Tell your doctor or pharmacist if you have side effects that don’t go away or become bothersome.
Mild side effects of methimazole oral tablet that occurred in studies include:
- unusual sensations, such as tingling or pins-and-needles feeling
- dizziness
- drowsiness
- hair loss
- headache
- itchiness
- joint pain
- loss of taste
- minor rash
- muscle aches
- nausea or vomiting
- swelling
- upper belly pain or discomfort
- mild allergic reaction*†
* To learn more about this side effect, see the “Side effects of methimazole in detail” section below.
† An allergic reaction is possible with methimazole oral tablet. But it’s unclear whether it occurred in the drug’s studies.
Methimazole oral tablet may cause more mild side effects than those listed above. For details, see the drug’s prescribing information.
Serious side effects of methimazole
Methimazole may cause certain serious side effects. If you have any serious side effects from methimazole oral tablet, call your doctor right away. But if you think you’re having a medical emergency or your side effects feel life threatening, take immediate action. Call 911 or a local emergency number, or go to the nearest emergency room.
After the Food and Drug Administration (FDA) approves a drug, it tracks and reviews side effects of the medication. Visit MedWatch’s website if you’d like to notify the FDA about a side effect you’ve had with methimazole.
Serious side effects of methimazole oral tablet that occurred in studies include:
* To learn more about this side effect, see the “Side effects of methimazole in detail” section below.
† An allergic reaction is possible with methimazole oral tablet. But it’s unclear whether it occurred in the drug’s studies.
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Common questions about side effects of methimazole
Here are answers to some common questions about side effects of methimazole oral tablet. If you have other questions, talk with your doctor or pharmacist.
Can methimazole be used in cats? If so, does it cause certain side effects in cats compared to humans?
Yes, there is a form of methimazole that is approved for use in cats to treat overactive thyroid. It is a special version of the drug that is made for use only in cats.
Talk with your veterinarian (vet) to learn more about using methimazole in cats, including what side effects to expect. Do not administer methimazole or any other medications to your pet without talking with your vet.
Does methimazole cause long-term side effects?
Long-term side effects are possible with methimazole oral tablet. Long-term side effects that have been seen with methimazole include:
- agranulocytosis
- liver damage (this side effect may have long lasting effects in some cases)
- vasculitis
These side effects can occur at any time, even if you’ve been taking methimazole oral tablet for a long time without side effects. Talk with your doctor if you have more questions about possible long-term side effects with methimazole.
Is weight gain a side effect of methimazole?
No, weight gain wasn’t reported in studies of methimazole oral tablet. But methimazole oral tablet treats an overactive thyroid, and weight loss can be a symptom of overactive thyroid.
Taking methimazole oral tablet will help your thyroid return to working the way it should. And this may cause you to regain some weight.
Also, it’s possible for your thyroid to become underactive while taking methimazole oral tablet. Weight gain can be a symptom of an underactive thyroid. You can learn more about this side effect in the “Side effects of methimazole in detail” section below.
If you have unusual weight gain, tell your doctor. They can determine the most likely cause and suggest ways to manage it if necessary.
Side effects of methimazole in detail
Below you’ll find details on some of the side effects of methimazole oral tablet.
Liver damage
In studies, liver damage was rare in people taking methimazole oral tablet. This side effect may be serious.
With methimazole, liver damage such as hepatitis (liver inflammation) and liver failure occurs. Symptoms of liver problems may include:
- itchiness
- jaundice (yellowing of the skin or whites of the eyes)
- loss of appetite
- upper right belly pain
Ways to manage
If you experience symptoms of liver problems, tell your doctor. They’ll likely recommend lab tests to check your liver function. If you develop liver problems with methimazole oral tablet, your doctor may recommend stopping the drug.
Underactive thyroid
In studies, underactive thyroid was seen in people taking methimazole oral tablet. This side effect is usually mild, but it may be serious.
Methimazole oral tablet treats overactive thyroid. But treating overactive thyroid with medications involves finding the right balance with the dose. Sometimes, due to the effect of the tablet, the thyroid hormone levels can become too low. It may lead to underactive thyroid (hypothyroidism). Symptoms may include:
- constipation
- dry skin
- fatigue
- feeling cold
- weakness
Ways to manage
Your doctor will order tests on a regular basis to keep a check on your thyroid levels while you take methimazole oral tablet. If necessary, they’ll adjust your dose to keep these levels in a target range.
If you experience symptoms of underactive thyroid, tell your doctor. They’ll likely recommend thyroid testing to check your thyroid levels.
Vasculitis
In studies, vasculitis, including periarteritis, has been reported in people taking methimazole oral tablet. This side effect may be serious.
With vasculitis, you experience inflammation of the blood vessels. This includes the veins, arteries, and capillaries. Periarteritis refers to a type of vasculitis that affects small- or medium-sized arteries. Arteries carry blood from the heart to the body’s organs and tissues.
Vasculitis can weaken blood vessels and cause them to leak. This can lead to damage of the skin, kidneys, lungs, brain, or nerves.
Symptoms of vasculitis may include:
- a new rash
- blood in the urine
- coughing up blood
- decrease in the amount of urine you make
- shortness of breath
Ways to manage
If you experience symptoms of vasculitis, tell your doctor right away. They’ll likely recommend stopping methimazole oral tablet. They may also prescribe medications to treat the vasculitis.
If your symptoms feel severe, seek immediate medical attention and go to a nearby emergency room or urgent treatment center. Although rare, vasculitis caused by methimazole can be severe and requires urgent care.
For some people, methimazole oral tablet can cause an allergic reaction. But it’s not clear whether this side effect occurred in the drug’s studies.
Symptoms can be mild or serious, and they may include:
- itchiness
- skin rash
- swelling under the skin, usually affecting eyelids, lips, hands, or feet
- swelling of the mouth, tongue, or throat, which can make it hard to breathe
- flushing (temporary warmth, redness, or deepening of skin color)
Ways to manage
For mild allergic reaction symptoms, such as a mild rash, call your doctor right away. They may recommend treatments to help manage your symptoms. They’ll also let you know whether you should keep taking the medication.
For severe allergic reaction symptoms, such as swelling or difficulty breathing, call 911 or your local emergency number right away. These symptoms require immediate medical care because they can become life threatening. If you’ve had a serious allergic reaction to methimazole oral tablet, your doctor may recommend taking a different medication instead.
Warnings for methimazole
Below are some factors you may want to discuss with your doctor before taking methimazole oral tablet.
Warnings
It may not be safe for you to take methimazole oral tablet if you have specific health conditions. These are sometimes called drug-condition interactions. Other things may also affect whether methimazole oral tablet is a safe treatment option for you.
Before taking methimazole oral tablet, tell your doctor about your health and the medications you take. Things to consider include:
Methimazole and pregnancy
Methimazole oral tablet should not be taken during the first trimester of pregnancy. If you’re planning a pregnancy or can become pregnant, talk with your doctor before taking this medication.
Methimazole and breastfeeding
It’s not known whether methimazole oral tablet should be taken while breastfeeding. If you’re breastfeeding or planning to do so, talk with your doctor before taking this medication.
Methimazole oral tablet is not known to interact with alcohol.
If you drink alcohol, talk with your doctor about whether it’s safe to consume it during your treatment with methimazole oral tablet.
What to ask your doctor
This article describes common and serious side effects of methimazole oral tablet. If your doctor prescribes this medication, they can discuss possible side effects with you. Let your doctor know if you have concerns or questions about treatment with this medication.
Here’s a list of some possible questions you may want to ask your doctor:
- Does my risk of side effects depend on the dosage you prescribe?
- Do I have a higher risk of side effects than other people?
- How do the side effects of methimazole oral tablet compare with other treatments for my condition?
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.
