Episode - The Impact of Methimazole and PTU on the Gut Microbiome


Many medications can have a negative impact on the gut microbiome, such as antibiotics and proton pump inhibitors, but did you know that the research shows that antithyroid medication can also affect the gut microbiome and the intestinal barrier? In this episode Dr. Eric will discuss the impact of both Methimazole and PTU on the intestinal barrier and gut microbiome.

During this episode you’ll learn:

  • Which drugs disrupt the gut microbiome
  • How methimazole and PTU affect the gut microbiome
  • How methimazole and PTU affect the intestinal barrier
  • Whether the gut can be healed after stopping antithyroid medication
  • If it’s possible to get into remission while taking antithyroid medication
  • Alternatives to antithyroid medication

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Here is the transcript for this episode:

Welcome back to the Save My Thyroid podcast. This is Dr. Eric Osansky. In this episode, I am going to discuss the impact of the antithyroid medications methimazole and PTU on the gut microbiome.

I’d like to start out by discussing what intestinal dysbiosis is. Dysbiosis is simply an imbalance of the gut flora. Taking oral antibiotics for infection will not only kill the harmful bacteria of the gut, it will also have a negative impact on some of the beneficial bacteria. This is an example of how someone might get intestinal dysbiosis.

However, some natural agents can also affect the good bacteria. Something to keep in mind. That’s not what the focus of this episode is, but it’s not just antibiotics that can have an impact. An example is oregano oil. It can be harsh on the good bacteria, even though I use it sometimes.

As far as certain drugs that can disrupt the gut microbiome, we all know the impact that antibiotics have. There is a time and place of course for antibiotics, but they are definitely overused and abused.

Proton pump inhibitors, or PPIs, also known as acid blockers, can also have a negative impact on the gut microbiome.

Metformin also has a negative impact. A number of years ago, I did not know this, not that I prescribed it, but if someone has a case of insulin resistance that is not responding to natural methods, in the past, I might have mentioned it. There is still a time and place for it,but I would definitely be more cautious. As I mentioned, I can’t prescribe it anyway.

Certain antipsychotics can disrupt it.

And then of course, antithyroid medication, which is the purpose of this episode, specifically methimazole and PTU. Those are the main types of antithyroid medication. Carbimazole is another type that is prescribed in some other countries. It converts into methimazole. I’m guessing that probably has the same effect, but there is no research that I have seen up until this point.

When should these drugs be taken? As you know, everything comes down to risk versus benefits. If you have a severe bacterial infection, then taking an antibiotic probably is necessary. There is a time and place for these other types of medications as well.

How do antithyroid medications affect the gut? Research showed that intestinal barrier structure and function were destroyed. This is with both methimazole and PTU. It also showed that the fecal and serum lipopolysaccharide levels in both the clinical and animal antithyroid drugs were higher than those in the control group. The increase in lipopolysaccharides, also known as LPS, was correlated with the change in blood indicators. Let’s talk about these. These are large molecules found in gram-negative bacteria. Multiple studies show that they can cause a leaky gut.

Then you have short chain fatty acid producing microbial constituents. Certain ones like lactobacillus, which is commonly found in probiotics, and an important part of your gut flora. These and some other microbial constituents that produce short chain fatty acids actually decreased after taking antithyroid medication. When it comes to short chain fatty acids, butyrate is the most important one. It’s been shown to increase regulatory T cells, which keep autoimmunity in check while decreasing TH-17 cells, which promote autoimmunity.

You might just want me to get to the point and tell you which antithyroid medications should be avoided since they can cause dysbiosis and disrupt the gut barrier. Just a reminder: everything does come down to risk versus benefits. While of course you want to do everything you can to preserve the health of the gut, we also need to keep in mind that it’s important to safely manage the hyperthyroid symptoms. That being said, there are other options.

It doesn’t mean everybody needs to take antithyroid medication. Some of you listening might know that when I dealt with Graves’ Disease, I did not take antithyroid medication. A lot of my patients do, so I am definitely not against people taking it. I took the herb bugleweed, which I’ve discussed before. Another natural agent with antithyroid properties is L-carnitine, which I have not taken. Some of my patients do take that. I do recommend bugleweed more commonly.

Should you stop taking antithyroid medication?  I can’t tell anybody to stop or even start taking antithyroid medication. That’s up to the prescribing medical doctor. I would just say to be cautious. You don’t want to have unmanaged hyperthyroidism. I was taking a risk when I took bugleweed. Thankfully, it worked. If it didn’t work, I would have considered taking antithyroid medication. As I have mentioned multiple times, there are risks to having unmanaged hyperthyroidism as well.

Another question you might have is whether or not the gut can be healed after stopping antithyroid medication. If someone starts antibiotics, and then they stop taking them, it is possible to heal the gut, which is a real good thing. A lot of people take antibiotics. Most people have taken antibiotics at some point in their life. I had my share of antibiotics when I was younger. If someone takes one or multiple rounds, and then they stop taking them, yes, the gut over time should heal. The same should be true with antithyroid medication. While you’re taking antithyroid medication, it will have its effects on the gut. Once you stop taking antithyroid medication, the gut should heal.

Is it possible to get into remission while continuing to take antithyroid medication? Over the years I have had many patients take antithyroid medication, different types, while addressing the cause of the problem. Many of these people eventually got into remission. For those people who don’t get into remission, it is possible that taking the antithyroid medication might have been the reason for this. This is something to consider. If someone continues to take antithyroid medication to manage a symptoms, and they are not getting into remission, it could be because the gut isn’t completely healed. Especially for those with Graves’, a healthy gut is important for a healthy immune system.

It’s a bit of a catch-22 situation. Those with hyperthyroidism want to be safe while addressing the cause of their condition, but it might be more challenging for some people to get into remission while still on antithyroid medication. This is especially true when taking higher doses. There is no research I am aware of that talks about different dosing. If someone is taking 40mg of methimazole, that is probably going to have a greater impact on the gut microbiome than someone who is only taking 5-10mg.

I want to briefly discuss some alternatives to antithyroid medication. In episodes two and three I go into greater detail. There is bugleweed and L-carnitine. L-carnitine, the research shows higher doses are necessary to have antithyroid properties, between 2,000-4,000mg a day. Lithium. Potassium iodide in higher doses also can have antithyroid properties. Very controversial though. I’m not recommending for anybody to take potassium iodide. LDN, this modulates the immune system. When it works, it can work really well. But it is more hit or miss.

If taking any of these, ideally work with a health care practitioner, probably a natural health care practitioner. If you go to an endocrinologist, they won’t recommend any of these. If you are looking into something like potassium iodide, you definitely want to consult with a natural health care practitioner.

Cholestyramine isn’t typically recommended for hyperthyroidism, but there are some research studies which show that it has antithyroid properties. It’s not the same as methimazole, PTU, or even bugleweed. It actually binds to the hormone. It’s a binder. I have had a couple of patients take it. And so it’s been a very small sample size. It is something to consider taking if you don’t want to take antithyroid medication. Let’s say the bugleweed doesn’t work. Maybe you’re willing to take antithyroid medication, but it causes side effects besides the impact of the gut microbiome. Once again, refer to episodes two and three for more information.

Now I would like to go ahead and summarize what I’ve discussed so far in this episode. Once again, certain drugs disrupt the gut microbiome. This includes not only antibiotics and PPIs, but unfortunately, antithyroid medication like methimazole and PTU. The research shows that antithyroid medication specifically destroyed the intestinal barrier and can cause a leaky gut. Antithyroid medication also decreased short chain fatty acids, and this is important to help prevent autoimmunity, to help keep autoimmunity in check. With that being said, there is a time and place for antithyroid medication. By no means did I put this episode together to discourage people from taking antithyroid medication. Everything comes down to risks versus benefits. That being said, there are alternatives to methimazole and PTU. I mentioned bugleweed, L-carnitine, LDN, cholestyramine. Refer back to episodes two and three for more information on the different alternatives.

I think that’s a wrap on this presentation. Just remember that while antithyroid medication can have a negative impact on the gut microbiome, there is a time and place fortaking methimazole and sometimes even PTU. That being said, I hope you found this information to be valuable. I look forward to catching you in the next episode.