Methimazole Side Effects You Should Know (2023)

Methimazole: What You Need To Know

Are you taking methimazole for hyperthyroidism?

If so, there are some things you should know about this medication.

For starters, how about the fact that it can have some serious consequences on your liver?

Or how about the fact that it can directly lead to weight gain?

These are just some of the potential side effects of methimazole.

In this article, you will learn…

  • How methimazole works to blunt thyroid function
  • How this negatively impacts thyroid function and may lead to low thyroid symptoms
  • The side effects of lowering your thyroid and what that means for you
  • The mild short-term side effects associated with methimazole
  • The long-term more serious side effects associated with methimazole
  • And what other therapies you should do while taking methimazole

Let’s jump in:

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Methimazole Helps Slow Down Thyroid Function

As someone with hyperthyroidism, you probably already have some idea of how methimazole works.

Methimazole is what is known as an anti-thyroid medication.

Its entire goal is to SLOW down thyroid function and to take you from the hyperthyroid state to the “normal” thyroid state.

We call the normal thyroid state euthyroidism but you don’t necessarily have to know that for the purposes of this article.

But what you should know is that it’s incredibly difficult for your doctor to take you from the hyperthyroid state to the normal thyroid state with methimazole.

Instead, most hyperthyroid patients who take methimazole end up in a LOW thyroid state (known as hypothyroidism).

The reason is simple:

It’s actually quite difficult to balance your hormones, especially your thyroid, with the use of a medication that you take by mouth once per day.

Methimazole is like a blunt object when you really need a sharp scalpel.

Despite this, doctors still use and recommend methimazole because it’s often thought that the low thyroid state (hypothyroidism) is safer than the high thyroid state (hyperthyroidism).

Because of this, methimazole is often the drug of choice to treat pretty much any hyperthyroid condition(1).

And there are a lot of people taking it.

If you are one of them, you need to be aware of the potential side effects and consequences of this medication…

Side Effects + What To Look Out For

The side effects associated with methimazole are not as clear-cut as you might think.

Because methimazole BLOCKS thyroid function you can expect it to have consequences that impact your thyroid.

These consequences are in addition to any symptoms you may experience directly from the medication itself.

Below I’ve split up the types of symptoms you may experience from methimazole into 3 different groups.

The first group is symptoms you may experience from slowing down your thyroid.

The second group is mild symptoms you may experience secondary to the medication.

And the third group is more serious symptoms you may experience if you use methimazole long-term.

#1. Methimazole May cause Low Thyroid Symptoms

Remember:

The whole purpose of using methimazole is to slow down your thyroid to take you out of the hyperthyroid state.

The problem here is that slowing down thyroid function isn’t a perfect science so it’s easy to slow down thyroid function too much.

(Video) Methimazole and Propylthiouracil (PTU) - Mechanism of Action, Indications, and Side Effects

If you slow down thyroid function too much you may swing from a hyperthyroid state to a hypothyroid state and experience any of these symptoms:

  • Weight gain
  • Hair loss
  • Fatigue
  • Cold intolerance
  • Constipation
  • Muscle or joint pain
  • Brittle nails
  • Menstrual irregularities
  • Depression

These are all symptoms of having a LOW thyroid.

It may seem weird that someone with hyperthyroidism can experience hypothyroid symptoms but believe me when I tell you that it happens all of the time.

Do not confuse THESE side effects/symptoms with the side effects of the medication itself.

They come from two very different reasons.

#2. Mild Side Effects Directly from Methimazole

Like any prescription medication, methimazole can also directly cause side effects.

These side effects are separate from the symptoms you may feel as you slow down your thyroid.

Side effects of taking Methimazole may include any or all of the following:

  • Upset stomach
  • Nausea/vomiting
  • Rashes or itching of the skin
  • Headaches
  • Drowsiness
  • Dizziness
  • Muscle or joint pain
  • Swelling
  • Hair loss

These side effects tend to be on the more mild side and are often related to your dose.

If you are experiencing any of these side effects then you can talk to your doctor about making changes to your dose.

#3. More Serious Side Effects from Methimazole

What you may not realize is that methimazole is NOT intended to be used long-term.

In fact, there are some serious side effects that may come about if you try to use methimazole long-term.

These side effects come from organ damage.

More serious side effects may include:

  • Liver damage
  • Yellow eyes or skin
  • Severe abdominal pain/stomach pain
  • Very dark-colored urine
  • Nausea/vomiting that doesn’t stop
  • Reduced urinary output (not urinating as much as you used to)

If you experience ANY of the side effects then you need to talk to your doctor immediately.

Methimazole & Weight Gain Explained

Another side effect that patients often experience when starting methimazole is weight gain.

How can you gain weight if you are hyperthyroid?

Shouldn’t hyperthyroid patients LOSE weight?

Well, yes, but also no.

Your thyroid is one of the main things in charge of maintaining your weight.

If your thyroid is in overdrive then your metabolism will be increased and you will lose weight (a side effect of hyperthyroidism).

Conversely, if your thyroid is slowed down then your metabolism will be decreased and you will GAIN weight (a side effect of hypothyroidism).

You can probably already see where I am going with this.

What does methimazole do to your thyroid?

It SLOWS it down.

And if you slow down your thyroid then you will necessarily slow down your metabolism in the process.

So it is VERY possible that you can have hyperthyroidism but be treated with methimazole AND gain weight.

In fact, it’s actually quite common.

(Video) methimazole

The mechanism isn’t that complicated either, it has everything to do with your thyroid.

Unfortunately, it can be very difficult to try and lose weight while you are taking methimazole.

Why?

Because you are fighting against a medication that is limiting your ability to succeed.

It’s like trying to run a race with a crutch.

It’s not impossible to lose weight while taking methimazole but it is very difficult.

If you are trying to lose weight then your best bet is to try and get off of methimazole.

Methimazole Shouldn’t Be Used Long-Term

If you are taking methimazole then you should be aware that this medication is NOT intended to be used long-term.

The usual recommended duration of therapy is somewhere around 18 to 24 months.

And the reason is simple:

As much as one-half of patients with hyperthyroidism will experience a relapse in their condition and no longer need it.

In this way, methimazole is really just used as a way to blunt the serious side effects of hyperthyroidism while giving your body time to fix whatever caused the hyperthyroid state to begin with.

Recently, some doctors have been recommending that hyperthyroid patients take methimazole for a longer duration of time (2).

This strategy requires a much smaller dose of methimazole but patients may have to take it for 60 to 120 months (3) (5 to 10 years).

I’m not a fan of this approach and I will provide some reasons why it may not be the best option below.

While methimazole is definitely effective at stopping the hyperthyroid state and reducing the symptoms associated with hyperthyroidism, long-term methimazole use may cause some serious consequences.

It turns out that your body needs thyroid hormone (surprise, surprise) and that reducing it below normal levels can have consequences on many organ systems in your body.

Long-term methimazole use may result in potential liver damage (4), changes to your bone structure (5), and more.

Methimazole Side Effects You Should Know (2)

It’s not a good idea to use methimazole unless absolutely necessary which brings me to my next point.

What Else Can you Do?

If you aren’t a fan of the potential side effects associated with methimazole use then what are you supposed to do?

Fortunately, there are a number of lifestyle changes that you can make which may have a positive impact on your thyroid.

But let’s go back to the goal of methimazole for a minute to help you understand.

To do this we need to talk about why doctors recommend methimazole.

The entire goal when using methimazole is to slow down your thyroid function and allow enough time to pass for your body to heal.

Using this strategy anywhere from 15 to 50% of patients may experience a relapse in their hyperthyroid symptoms and no longer need any therapy to treat their hyperthyroidism.

Sounds pretty good, right?

It does.

Methimazole Side Effects You Should Know (3)

But what if there was a way to increase the chance that your body goes into remission so that you do not need to take methimazole for anywhere from 2 to 10 years (depending on which approach you use)?

(Video) USMLE: What you need to know about Methimazole by UsmleTeam

That’s where natural therapies come in.

Making changes to your diet, taking dietary supplements, managing your stress, ensuring that you get enough sleep, and so on, may increase your odds of going into remission.

They also may allow you to get off of methimazole sooner rather than later (which would be ideal for most people).

And these natural therapies are incredibly safe and they are things that you are able to do on your own.

You don’t need permission from your doctor to eat more fruits and vegetables, avoid grains such as gluten, and make sure you sleep 8 hours per day.

These types of therapies are often overlooked by conventional doctors even though they are highly effective.

There are many therapies you can use depending on the type of hyperthyroidism that you have (Graves’ disease versus other conditions).

Final Thoughts

Methimazole is an anti-thyroid drug that is designed specifically to slow down thyroid function.

While it is great at managing the symptoms of hyperthyroidism (and consequences of this disease) it is not without side effects itself.

Side effects from methimazole tend to come from its effects on thyroid function or directly from the medication itself.

While methimazole can be effective it is not intended to be used long-term.

Even while taking methimazole you can take advantage of natural therapies such as improving your diet, avoiding gluten, reducing your stress, and taking supplements to help put your hyperthyroidism into remission.

These therapies are very safe and can be very effective.

Now I want to hear from you:

Are you currently taking methimazole?

If so, what type of side effects are you experiencing?

Do you think your side effects are coming from reducing thyroid function or directly from methimazole?

Have you tried using any natural therapies with methimazole? If so, which ones?

Leave your questions or comments below!

#1. https://pubmed.ncbi.nlm.nih.gov/16584027/

#2. https://www.mdedge.com/clinicianreviews/article/150048/pituitary-thyroid-adrenal-disorders/long-term-methimazole-therapy

#3. https://pubmed.ncbi.nlm.nih.gov/31310160/

(Video) METHIMAZOLE (TAPAZOLE) - PHARMACIST REVIEW - #206

#4. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4197171/

#5. https://pubmed.ncbi.nlm.nih.gov/28759749/

Methimazole Side Effects You Should Know (4)

FAQs

What should I monitor with methimazole? ›

Methimazole can cause hypothyroidism. [6] Therefore it is crucial to monitor T3 T4 levels in the serum, to adjust the dose to maintain a euthyroid state. In addition, since it crosses the placenta readily, it is capable of causing hypothyroidism and cretinism in newborns.

What are the long term effects of taking methimazole? ›

For Healthcare Professionals

Some of the more frequently reported adverse reactions have included skin rash, urticaria, nausea, loss of taste, and abnormal loss of hair.

How do you know if you're taking too much methimazole? ›

Overdose symptoms may include nausea, vomiting, upset stomach, headache, joint pain, fever, itching, swelling, or pale skin and easy bruising or bleeding.

How does methimazole make you feel? ›

Feeling sleepy. Headache. Muscle or joint pain. Hair loss.

Why is methimazole hazardous? ›

Methimazole has been classified as hazardous because the medication impedes the body from using iodine to make thyroid hormone, thereby inhibiting synthesis of the hormone. The drug may cause birth defects and has been found to cause cancer in rodents.

What is the safest treatment for hyperthyroidism? ›

Radioactive iodine treatment

It's a highly effective treatment that can cure an overactive thyroid. You're given a drink or capsule that contains iodine and a low dose of radiation, which is absorbed by your thyroid. Most people only need a single treatment.

Does methimazole cause anxiety? ›

Comparisons between treated and controls took place between 10 and 30 days postfertilization to examine times both during and after treatment. Using the novel tank and startle response tests, we found that anxiety behaviors are significantly increased following MMI treatment.

Can you stop methimazole suddenly? ›

Skipping or stopping your antithyroid medication or thyroid hormone replacement will lead to undesirable and possibly dangerous effects. Not taking your medication also increases your risk of fatal conditions like myxedema coma if you are hypothyroid, and thyroid storm if you are hyperthyroid.

How many years can you take methimazole? ›

A recent randomized clinical trial reported that 5-year continuous methimazole (MMI) therapy is accompanied with 84% remission up to 4 years after drug withdrawal [14]. However, the optimal duration of ATD therapy is still debatable.

How long should a person take methimazole? ›

“Long-term, low-dose methimazole treatment for 60-120 months is a safe and effective treatment for Graves hyperthyroidism and is accompanied by much higher remission rates than the usual 18-24 months of methimazole treatment,” he summarized.

Is methimazole safe long term? ›

Long-term therapy with methimazole is not usually considered in treating patients with a toxic nodular goiter since this will never go into remission. However, methimazole has been shown to be safe for long term use in patients with Graves' disease.

How can I avoid weight gain on methimazole? ›

Sometimes it may be possible to simply reduce your dosage which will allow some thyroid hormone activation and production in your body. A small change in your dose may be sufficient to restore some thyroid function (without causing the symptoms of hyperthyroidism) which can help manage your weight.

Is 10 mg of methimazole a lot? ›

Typical dosing for methimazole (Tapazole)

The dose of methimazole (Tapazole) for adults ranges from 5 to 40 mg by mouth per day depending on how severe your hyperthyroidism is. The dose is taken in 3 divided doses every 8 hours.

When should I stop taking methimazole? ›

"In our practice, we usually discontinue methimazole for 48 hours before radioiodine use with good results," he says. The researchers, from Imam Reza Hospital and other facilities in Mashhad, Iran, evaluated 151 patients with Graves' disease, ranging from 18 to 65 years old.

How long does it take your body to adjust to methimazole? ›

Methimazole requires an average of six weeks to lower T4 levels to normal and is often given before radioactive iodine treatment. Methimazole can be taken once per day. Propylthiouracil — Propylthiouracil does not reverse hyperthyroidism as rapidly as methimazole, and it has more side effects.

Can methimazole make you feel sick? ›

Minor adverse reactions include skin rash, urticaria, nausea, vomiting, epigastric distress, arthralgia, paresthesia, loss of taste, abnormal loss of hair, myalgia, headache, pruritus, drowsiness, neuritis, edema, vertigo, skin pigmentation, jaundice, sialadenopathy, and lymphadenopathy.

Can methimazole make you depressed? ›

2 patient evaluations for Methimazole

Advice & Tips: For the strangest reason, it made me really really depressed. to where i would stop taking them, and went to doc he only lowered the dose, and depression take a little longer,but for 4 months i took it like they wanted and hopefully its normal again.

Why do you have to wear gloves with methimazole? ›

The main reason for wearing gloves and washing hands is to avoid accidentally ingesting any drug residue on the hands, Alvey said, but she noted that methimazole presumably can be absorbed through the skin as well, since the medication often is compounded into a transdermal product.

What happens if you take methimazole and don't need it? ›

The more concerning issue of taking thyroid medication when you don't need it lies in the possible side effects, including: Irregular heart rhythms. Rapid heart rate. Symptoms of heart failure (shortness of breath, swelling, unexpected weight gain)

Should you wear gloves when handling methimazole? ›

If you are administering methimazole transder- mal gel, you should wear gloves and wash hands after handling. Owners who have low thyroid function should be very careful when handling this drug and should avoid all skin contact with the drug.

What happens if you take methimazole and don't need it? ›

The more concerning issue of taking thyroid medication when you don't need it lies in the possible side effects, including: Irregular heart rhythms. Rapid heart rate. Symptoms of heart failure (shortness of breath, swelling, unexpected weight gain)

What happens when you stop taking methimazole? ›

If you skip or stop your medicine entirely, you can experience a number of short-term and long-term consequences, including: Debilitating weight loss. Dramatically increased appetite and thirst. Nervousness, anxiety, panic attacks.

How can I avoid weight gain on methimazole? ›

Sometimes it may be possible to simply reduce your dosage which will allow some thyroid hormone activation and production in your body. A small change in your dose may be sufficient to restore some thyroid function (without causing the symptoms of hyperthyroidism) which can help manage your weight.

Is it better to take methimazole in the morning or at night? ›

by Drugs.com

Often patients are advised to take thyroid medication in the morning 30 to 60 minutes before breakfast, but you can take it in the evening on an empty stomach if this suits your lifestyle better.

Can you drink coffee with methimazole? ›

In studies, coffee reduced the body's absorption of thyroid medications by about 30%. That's why experts recommend that you wait at least 60 minutes after drinking coffee to take your thyroid replacement medication. After taking your thyroid med, you should also wait at least an hour before drinking coffee.

How long can you be on methimazole? ›

A recent randomized clinical trial reported that 5-year continuous methimazole (MMI) therapy is accompanied with 84% remission up to 4 years after drug withdrawal [14]. However, the optimal duration of ATD therapy is still debatable.

Does methimazole cause anxiety? ›

Comparisons between treated and controls took place between 10 and 30 days postfertilization to examine times both during and after treatment. Using the novel tank and startle response tests, we found that anxiety behaviors are significantly increased following MMI treatment.

How long until methimazole is out of your system? ›

The elimination half-life is approximately 5—9 hours. However, the intrathyroidal residence of methimazole is roughly 20 hours, and the duration of action 40 hours, which allows once-daily dosing some patients. The plasma elimination half-life of methimazole is not appreciably altered by the patient's thyroid status.

Is 10 mg of methimazole a lot? ›

Typical dosing for methimazole (Tapazole)

The dose of methimazole (Tapazole) for adults ranges from 5 to 40 mg by mouth per day depending on how severe your hyperthyroidism is. The dose is taken in 3 divided doses every 8 hours.

Does methimazole make you weak? ›

sudden weakness or ill feeling, fever, chills, sore throat, cold or flu symptoms; painful mouth sores, pain when swallowing, red or swollen gums; or. pale skin, easy bruising, unusual bleeding.

Does methimazole make it hard to lose weight? ›

Some medications healthcare providers prescribe for thyroid-related symptoms or other conditions can cause weight gain. The following medications are associated with weight gain: Antithyroid drugs: Tapazole (methimazole) and PTU (propylthiouracil)

Can methimazole make you depressed? ›

2 patient evaluations for Methimazole

Advice & Tips: For the strangest reason, it made me really really depressed. to where i would stop taking them, and went to doc he only lowered the dose, and depression take a little longer,but for 4 months i took it like they wanted and hopefully its normal again.

Can you be fat with hyperthyroidism? ›

Overweight or obesity was observed in 76.5% and 58.8% of hypothyroid and hyperthyroid patients, respectively (p=0.23).

When is the best time to take methimazole 10 mg? ›

To make sure that you always get the same effects, try to take methimazole at the same time in relation to meals every day. That is, always take it with meals or always take it on an empty stomach.

Does methimazole cause joint pain? ›

There have been a few reported cases of Methimzaole induced serum sickness. In one case, a 15-year-old boy was admitted to the hospital with joint pain and swelling of his ankles and knees after starting Methimazole 3 weeks prior for hyperthyroidism. Symptoms resolved upon stopping Methimazole [1].

Can you take vitamins with methimazole? ›

No interactions were found between methimazole and Vitamins. However, this does not necessarily mean no interactions exist. Always consult your healthcare provider.

Videos

1. Effectiveness of Thyroid Medications: Mayo Clinic Radio
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2. Part 2 of My Graves Disease Story- Methimazole & Rare Side Effect
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4. Long-Term Use of Antithyroid Medications
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