Frequently Asked Questions

This page is to have clear-cut answers to frequently asked questions.  If you want more detail into these answers, I suggest following links provided.

1. What problems can metronidazole toxicity cause?

The short answer is that metronidazole potentially causes dysfunction and/or damage to the brain and also the nerves throughout the body.  Any toxicity-related issue of the brain is called neurotoxicity and any issue with the nerves is called neuropathy.  The blanket term for any brain dysfunction is “encephalopathy.”

2. How common is metronidazole toxicity?

According to Oxford, at least 1 in 400 patients who take metronidazole will end up having an adverse reaction severe enough they will end up in the hospital.  In our support group, we believe the true number is much higher, and even Oxford notes that they also believe 1 in 400 is an under-estimation.  But their number at least provides a baseline.  To read the article, click here.

3. What are the symptoms of metronidazole toxicity?

There are over 50 symptoms of metronidazole toxicity we know about.  I have a video that goes into this in detail, which you can find here.  But this is the list from most common to least common:

4. These symptoms seem so random—why?

Because when the brain is affected, the sky is the limit on what symptoms you can have; however, when you take one step back, almost all of these symptoms fall into four main categories:

• Cerebellar dysfunction (dysfunction of the cerebellum)
• Dysautonomia (dysfunction of the brain stem)
• Altered Mental State (related to dysautonomia and overall brain dysfunction)
• Neuropathy (nerve damage)

5. How long does it take for metronidazole to get out of the body?

48 hours after discontinuation.

6. Okay…so if the drug’s out of my system, why I am still sick?

Because the drug has caused dysfunction and/or damage.  If you put your hand in fire, let it burn and then take the fire away, your hand is not okay despite the removal of the fire.

7. I only took metronidazole for a few days—can I really be this sick that quickly?

Yes.  We did a survey in our support group, and over 90% of patients had their adverse reaction to metronidazole in less than a week of use.  The most common day to have the reaction was day 5 of ingestion, with day 2 being the second-most common. 

8. But my doctor says you can only have toxicity after prolonged use.

Your doctor is wrong.  According to the systematic review “Metronidazole-Induced Central Nervous Toxicity,” the dosage and duration of time for taking metronidazole do not correlate with an adverse reaction.  In other words, the idea that it takes a long time using the drug in order for an adverse reaction to happen is a myth.

9. Okay, but what about dosage? So the amount of metronidazole I took doesn’t matter?

It’s hard to say definitively, but according to the systematic review referenced above, the dosage does not correlate with having an adverse reaction to the drug.  Some people with this toxicity took only a few small doses and had a severe reaction, and others took larger doses and had a milder reaction.

10. Could I die from metronidazole toxicity?

This is highly unusual, even in medical literature.  While there are a few cases of the toxicity causing death, it’s considered rare and there are no reports of someone stopping the drug and then dying days or weeks later.

11. But I feel like I’m dying. Should I go to the ER?

That is up to you.  But if you feel you need to go, please do so.  I went to the ER three times during the first 2 months of my toxicity, so no judgment here!  It’s okay to be scared—metronidazole toxicity can be pretty terrifying.  One recommendation, whether you go to the ER or see your primary care physician, is to remain as calm as possible and write down all your symptoms before you go so you remember what to discuss.

12. I went to the ER, I saw my doctor…but no one believes that metronidazole can cause this.

I understand and I’m sorry to say, but that is the overwhelming response from conventional medicine.  84% of metronidazole toxicity sufferers are not believed by their physicians.

13. But medical literature says metronidazole can be neurotoxic and/or cause neuropathy, right? Don’t doctors believe medical literature?

Yes, when it comes to it happening to “other” patients.  But not theirs.  They either don’t know that metronidazole can cause these adverse effects or they believe an adverse reaction is so rare, it can’t happen to their patients.  Stop me if you’ve heard one of these lines:

• “Flagyl can’t cause this.”
• “I’ve never seen Flagyl do that before.”
• “Yeah, but a reaction like that is just so rare…”
• And my favorite: “Well, even if you’ve had a reaction, you should be fine by now.”

I’m sorry your doctor doesn’t believe you.  We have a support group that is for people suffering from metronidazole toxicity; make sure to answer both questions to request to join:

https://www.facebook.com/groups/1234759023201741

14. How about you? Are you a medical professional?

No, I’m not.  I happen to be an assistant for doctors, including researchers, and have access to a medical library.  I’ve also been a contributing writer on-and-off for 3 medical magazines since 2006, which has helped me learn how to research and read medical literature.  But this doesn’t make me a medical professional.  You will need to follow links provided on this site, do your own research, and make decisions for what is best for you.

15. Medical literature says that metronidazole toxicity can cause white matter lesions on the brain—are they causing my symptoms?

Most likely, no…or at least they are not the central cause.  While having lesions on the brain is obviously bad, they almost always go away quickly after discontinuing metronidazole, even if symptoms continue.  This means that the correlation between the resolution of lesions and the resolution of symptoms is poor, meaning that they might not be contributing to any symptoms at all.  But more research is needed.

16. Should I get a CT scan or MRI to check for lesions?

Again, that is up to you.  It’s not a bad idea to do a “process of elimination” to make sure there’s not something else going wrong with your body that’s causing symptoms.  However, a CT scan does not typically pick up on the lesions caused by metronidazole toxicity.  An MRI can detect lesions, but as stated above, if you’ve discontinued the drug, there’s little chance lesions will show up, as they usually disappear quickly, even just a few days after stopping the medication.

17. So how can you test for metronidazole toxicity?

There is no official test.  If your doctor makes a diagnosis, it will need to be based on symptoms.  While an individual test might find an abnormality (like low potassium or small fiber neuropathy), connecting that diagnosis to metronidazole toxicity is another step, and most doctors do not make that connection.

18. So what is really happening that’s causing metronidazole to be toxic in my body?

There are a few theories in medical literature:

• Metronidazole destroys thiamine in the body (thiamine is vitamin B1)
• Metronidazole causes free radicals in the body, which can damage the RNA (a part of DNA).
• There is some evidence metronidazole can inhibit vitamin B3, which might be related to the destruction of vitamin B1.

There are other theories, but B1 deficiency has been discussed as the top suspected culprit in medical literature for three decades, with free radicals being the second-most discussed.

19. Okay, but why did this happen to me? I know someone who took metronidazole and they’re just fine.

We don’t know why one person has an adverse reaction to metronidazole and another person does not.  Just like we don’t know why one person can have a lethal peanut allergy but most people do not.  Or why someone gets lung cancer at 40 and never smoked, but someone else lives to 90 and smoked all their lives.  There is most likely an answer out there as to why you had this toxic reaction, but again, more research is needed.

20. Can I heal from metronidazole toxicity?

Yes.  Most people with metronidazole toxicity either make a full recovery or greatly improve over time.

21. How long does it take to heal?

It depends on how severe the reaction was, how long you went without treatment, and how much damage—if any—occurred.  Some people only have dysfunction causing symptoms, so once the dysfunction stops, they recover quickly.  Usually, recovery takes a few weeks to several months, with gradual improvement seen throughout that time.  Neuropathy takes the longest time to heal and might not heal fully, because neuropathy is damage to the nerves that resulted from dysfunction.  Other symptoms seem to be a mix of the two—dysfunction and some damage.

22. You said there’s a treatment—what is the treatment for metronidazole toxicity?

Because metronidazole destroys vitamin B1 (thiamine) in the body, this causes a deficiency of B1, which leads to a condition called “thiamine deficiency disease.”  The symptoms of thiamine deficiency disease and metronidazole toxicity are identical, so the treatment is to restore the lost thiamine in the body.  See the blog’s Treatment Page for more details, but you will need:

• Thiamine
• Magnesium (you need magnesium to activate thiamine in the body)
• Down the line, a good B-complex (a supplement with all the other B-vitamins, with B6 that’s not too high)

23. Why a low B6?

B6 is the only B-vitamin that, if taken at high doses long-term, can damage nerves.  Personally, I like Nature Made Super B-Complex; it might not be available in your region, but it’s a good reference regardless when it comes to a good B-Complex.  Nutritional yeast is another good source of B-vitamins.

24. Okay, so how do I take this “thiamine regimen”?

I have a video on YouTube that goes into everything about metronidazole and thiamine, and I highly recommend that you watch it (click here).  If you are very deficient, you don’t want to “shock” your system by taking tons of thiamine to start.  But eventually you will most likely have to take very high doses of thiamine to fix this problem; here are some examples of how to do that, but again, I am not a medical professional, so this is just advice from one patient to another:

Regimen 1 with thiamine HCL (water soluble), built up to Lipothiamine (fat soluble) and Allithiamine combo.  Lipothiamine and Allithiamine are mostly the same, so you can combine them or choose not to.

Regimen 2: Same but with only Allithiamine (this is the one I did):

Regimen 3: A slower build-up of thiamine.  Again, you can use Allithiamine or Lipothiamine:

Regimen 4: A very slow build up, usually for patients concerned about a paradoxical reaction.  You start with thiamine-rich nutritional yeast, then slowly build up to water soluble thiamine and then to a fat soluble thiamine called “benfotiamine.”  Benfotiamine is not as strong at Lipothiamine or Allithiamine, but some members in our support group like it the best:

25. Okay…but what is allithiamine, benfotiamine and lipothiamine?

They are special “fat soluble” versions of thiamine, derived from garlic.  All other forms are what is called “water soluble,” and it’s the water soluble versions you’ll find at your local grocery store or pharmacy.  The only difference between these two is that fat soluble thiamine can get through the wall of your cells without help from the body, making it much stronger than regular water soluble thiamine.

26. Wow, that is a LOT of thiamine to take. Can it be toxic?

Not likely.  There is actually no limit to how much thiamine you can take.  Because it’s more common, water soluble thiamine has been studied for decades and there’s no reports of toxicity—about 1 in a million people will be allergic to super-high doses of thiamine.  However, because fat soluble is less studied, it’s always good to err on the side of caution.  And again, do your own research and decide what works for you.

27. How about magnesium—should I take really high doses of that?

No!  Magnesium is not water soluble.  It is a mineral and you can overdose on it.  Never take more than what is recommended on the bottle at the most.  And avoid magnesium citrate if possible—it can help but it’s also used as a laxative.  There are better magnesium supplements out there.

28. What better magnesium supplements?

Here is a chart we use in group. People usually go with magnesium L-threonate or magnesium glycinate, depending on symptoms.

29. Well, how much do you take, then?

As of right now, 2023, I take 300 mg’s of allithiamine (150 mg’s in the morning, 150 mg’s at night), one capsule of magnesium L-threonate and my Nature Made Super B-Complex in the morning.  However, I have switched up this regimen many times, testing different types of thiamine and magnesium, but this—right now—seems to be best for me.

One note: until your body adjusts to thiamine, don’t take it past dinnertime.  It has a calm energy to it that can make you perk up, so don’t take it at bedtime just yet.

It’s very trial and error, but always start small and build up.

30. Blah! I want to be all better now—I’ll just take a super-high dose of thiamine to start and I’ll heal faster.

Stop right there, my friend!  I wasn’t joking when I said starting on high doses of thiamine is a bad idea—you could have a paradoxical reaction.  Your body is now used to having low thiamine, so if you take high doses out of the blue, you risk making your symptoms worse.  Think about being thirsty: having a cup of water is great!—but having a tsunami of water is bad.  They’re both water, but one will help and one will harm.  Don’t jump in front of the tsunami just because you’re thirsty.  Gentle sips, my friend.  Click here to see the section of my video that goes into more details.

31. Wow, a paradoxical reaction sounds scary. Why would thiamine do this?

It’s not thiamine that’s the problem.  It’s your body that is now dysfunctional, and it’s been so deprived of thiamine, it’s just trying to function as best it can.  You can have a paradoxical reaction to anything—any nutrient out there, if you’re deficient enough.  In fact, having a paradoxical reaction proves that thiamine is the issue, and is a good sign that your body can still react and use thiamine, meaning a better chance of recovery.

32. But why would thiamine deficiency disease cause all these crazy toxicity symptoms, anyway? It’s just a stupid vitamin!  It can’t do all this!

Thiamine is an essential nutrient that your body requires to live.  In your cells, you have little factories called mitochondria, and these mitochondria convert food into energy.  There are 17 nutrients required to make this conversion happen and—you guessed it—thiamine is the first step of this long chain, along with magnesium.  Without thiamine, the factory shuts down, dysfunction occurs, and the result is damage in the body.  The places most vulnerable are areas with the highest concentration of mitochondria, with the back of the brain being the biggest one.

In its most extreme cases, thiamine deficiency can be fatal.  Also called “beriberi” in the early 1900s, there was a massive B1 deficiency in Japan after they switched from brown rice (full of B1) to white rice (no B1).  A quarter of a million people died.

Now, in all truth, your thiamine deficiency disease is probably mild to moderate with metronidazole, but that just shows how serious this deficiency is.  So yes, it can cause all of your symptoms.

33. Okay, fine. I’ll just go to my doctor and get a B1 blood test to check for deficiency.

If it were only that simple.  It’s fine to go to your doctor and ask for a blood test; if it comes back positive for deficiency, there’s your confirmation.  However, only 10% of thiamine stores are in blood, with the rest in your mitochondria, bone, tissue, etc—places well hidden from a test like that.  In addition, you cannot supplement thiamine within at least 3 days of the test (some tests require 7 days) and the test is considered insufficient for checking for thiamine stores in your body regardless.  Urine tests are not any better.  The most accurate tests are ones that go into your cells to check for deficiency, but they are expensive and availability is limited.  Ultimately, B1 tests in standard doctor offices are more security theater and lack accuracy.

Click here to for the part of my video that discussses this topic. 

34. Then how do I know I have thiamine deficiency?

How do you know you have metronidazole toxicity?  You know something is seriously wrong with your body, but all the tests are coming back normal and your doctor is trying to convince you metronidazole can’t do this.  There is 60 years of medical literature connecting metronidazole to brain and nerve toxicity; there is 30 years of medical literature connecting metronidazole to destroying thiamine and causing thiamine deficiency. 

You can make conclusions based off of symptoms.  Many diseases are diagnosed this way.

35. Can I heal without supplementing?

Yes, it’s possible but unlikely.  Your mitochondria have three key enzymes that require thiamine to function and if they are not damaged due to thiamine deficiency, then once you stop metronidazole and begin eating normally, you will slowly restore the thiamine, and your enzymes will not longer be starved.  But if the enzymes are compromised in any way—if the mitochondria aren’t capable of functioning properly or your gut is not capable of absorbing enough thiamine due to bad gut flora, SIBO or just imbalance due to antibiotics or other drugs—then that little bit of thiamine you get in food won’t fix the problem.

36. But I don’t want to take high doses of thiamine! I’ll just take 100 mg’s daily and see what happens.

That is your decision, but don’t expect much of a result.  Taking high doses of thiamine is not my recommendation—Dr. Derrick Lonsdale and Dr. Chandler Marrs, authors of “Thiamine Deficiency Disease, Dysautonomia, and High Calorie Malnutrition” discuss taking high doses of thiamine in their medical textbook and why it’s essential to fixing this deficiency.  Dr. Lonsdale is so renowned for his research into thiamine deficiency disease, the World Health Organization references his work on this very topic.  He’s also a member of our support group.  He has expressed in print many times why “megadosing” thiamine is crucial for the majority of people with this condition.

37. Fine, I’ll supplement thiamine at high doses. Will it cure my metronidazole toxicity?

Not necessarily.  Thiamine deficiency causes dysfunction and that dysfunction leads to damage.  Thiamine can potentially stop the dysfunction, but once the damage is there, it’s there.  This is why neuropathy is the hardest to treat—it is all damage that resulted from dysfunction.

Your body will need time to heal and it’s possible it won’t heal 100%.  It’s a very individual process.  But like I said earlier, most people do recover or at least improve from this condition.

38. How long will I have to take thiamine?

If you treat this quickly and your toxicity wasn’t too severe, then it’s very possible you will only need to supplement for a few months.  But this will take time: we see people in group take thiamine, get all better quickly, stop thiamine after only two weeks and then after another few weeks, boom!—full relapse.  Your symptoms will disappear long before the deficiency is fixed, so taking thiamine for a few months is the least amount of time to be expected.  You don’t want to be skating on the edge of this deficiency, feeling all better for a few weeks or a few months, and then end up having a relapse.  Remember, you are asymptomatic long before you’re cured.

39. Do some people have to take thiamine forever?

Yes and I’m one of them.  I’ve been supplementing since late 2017.  I went one week without thiamine in Fall of 2022 for a research study for a friend, and some of my old symptoms returned, including the tremor in my left hand (thought that one was long-gone!).

If your toxicity is severe and/or chronic, this could happen.  But don’t fret too much—there are no side effects once you get past any paradoxical reaction (and there’s a good chance you won’t even have a paradoxical reaction if you build up slowly).  It’s just a nuisance to take and if it rids you of your toxicity symptoms, then it’s worth the annoyance, believe me.

40. But why would you have to supplement forever?

Theoretically, it’s because the three enzymes in your mitochondria (and/or the mitochondria themselves) are damaged and can no longer use thiamine as efficiently as they used to.  You need to give them an extra hand moving forward.  But again, this usually only happens in severe and/or chronic cases, and my case was chronic.

41. I want to learn more about thiamine, my mitochondria and metronidazole.

Perfect!  I have a Treatment Page on this blog and a channel on YouTube to help you out (Part III goes into the thiamine).

https://www.youtube.com/@themetronidazoletoxicitych8037 

42. The video is 2 hours long—blah! So boring!

When I suffered my metronidazole toxicity in 2015, there were no videos.  There was no blog or support group.  It took years to compile this information that is now at your fingertips.  Remember this: no one cares more about your health than you do.  So if you’re not willing to learn and to try to help yourself, no one else is going to put forth more effort than you.  Don’t be complacent in your condition, especially when metronidazole toxicity is one of the few adverse drug reactions that has the potential to be treated.  You must be your own health care advocate!

43. Can I private-message you and ask you about my specific situation?

One of the reasons I created this blog and the videos is because I can no longer keep up with private messages.  I have a full-time job and life away from the support group, so while I do understand the need to reach out, I’m asking that you request to join our group and ask questions to everyone there.  As of Spring 2023, there are over 2,800 members, many with experiences similar to yours.  I’m not the only one who understands your situation, and I’m not the only one with suggestions on what to do.  Also, I check the group daily, and I do response there regularly.

44. Is there a chance the treatment won’t work at all?

Yes, but that’s not common.  If you have other pre-existing conditions or your metronidazole toxicity has caused significant damage to your nerves, brain and mitochondria…I’m sorry to say, but it’s possible that thiamine just isn’t enough anymore.  But I have seen many people who have struggled, who were house-bound, who were so anxiety-ridden they couldn’t even participate in group, and then I’d get a random message or see a post in group from them, talking about their recovery.  My personal favorite was one guy who constantly posted, talking about all his struggles with this for almost a year, and then this one random day, he private messaged me, “All healed now.”

Okay!  Well, that’s great—share that with group!  Stories like that happen all the time.  And remember, people who have recovered fully don’t need a support group.  Many leave without telling us they are better (bad on them, but it’s commonplace).

45. You talked about taking a B-complex, too. Why?

Because imbalances in thiamine (either high doses or deficiency) can imbalance the other B-vitamins.  These vitamins work together, so when one is off, all will be imbalanced, too.  This is one reason why people jump to the most popular B-vitamin out there, vitamin B12.  But you need B1 as the stepping stone to get B12 to work properly.  I usually recommend to start B1 and magnesium first, build it up, improve that deficiency, and then start a B-complex. 

46. When should I add a B-complex to my regimen?

There’s no exact timetable—again, this is very trial and error.  But you can try it a month or two into your thiamine regimen and see if it helps.  I started mine very late, about 7 months into my regimen, and I wish I’d started sooner.  I saw a jump in improvement after adding the B-complex.  But typically nutritional therapy is slow-going.

47. I can’t stand waiting weeks or months for this to work! Should I take drugs to help with the symptoms?

I understand.  It’s very possible that starting thiamine and magnesium will help after just a few weeks, but it is usually a slow process of healing.  Some people do have to resort to prescriptions to help mask symptoms, especially the anxiety and insomnia.  A few suggestions:

• Avoid benzo drugs like Valium unless you can take it only “as needed.”
• Take the lowest dose of any antidepressant, benzo, or gabapentin you can manage. This will make it easier to stop the medications later on.
• If you end up on an one of these drugs long-term, never stop it cold turkey. Always taper off slowly, even if it takes months.

When I first had my reaction, I tried several medications to help with the altered mental state.  I ended up in a psychiatrist’s office, so desperate for relief and crying so hysterically that I almost vomited into his trash can.  I’ve been there—metronidazole toxicity is hell.  He prescribed me mirtazapine, which is an antidepressant with a sedating quality.  Most general physicians do not know about this drug, so you might have to see a specialist.  It did help me greatly and when I tapered off slowly, I had no withdrawal issues, but another drug might work better for you.  Again, if you are suffering from this toxicity, we have a support group of over 2,800 members who might be able to offer their recommendations.

48. Is there anything else that can be done to treat metronidazole toxicity?

While thiamine and magnesium are obviously my first go-to for treatment, other members in our group have other suggestions.  Here is a short-list I’ve heard has helped some of them:

• Taking vitamin B3 might be beneficial because metronidazole has a negative effect on B3. But I would start B1 and magnesium first, build up some, before adding it.
• Some people in group have seen improvements with vitamin B12, but I don’t recommend starting with it, as again, you have to have your B1 improved before B12 can work properly.
• Lion’s Mane for neuropathy. I have not taken this myself, but some people in group have seen positive results.
• Metronidazole can cause potassium deficiency, which is a symptom of thiamine deficiency disease.  In the US, never get potassium in a capsule—the FDA has strange rules when it comes to potassium and capsule’s dosage levels are too low.  Instead, get a powder; I use if Dr. Berg’s Electrolyte Powder. But just like magnesium, you can overdose on potassium, so never take more than what’s recommended on the bottle.
• There are supplements out there strictly for mitochondrial health. I have not tried them myself, but you can Google “mitochondria supplements” and there should be options.
• Vitamin D3 with K2. Especially if you’re stuck indoors a lot right now, this might be a good supplement to add.
• Turmeric, with a 95% active curcumin. This is an anti-inflammatory.

These are just some suggestions, and are not part of the thiamine regimen.

49. Should I avoid any foods that could deplete vitamin B1?

Yes.  Here is a list of foods to avoid:

• Alcohol
• Coffee (the coffee itself, so decaf is still a no-go)
• Tea
• Sugar (try to cut back as much as you can—it’s hard to avoid).
• Smoking
• Certain raw fish (sushi)

Pretty much, all the fun stuff!

50. Wow, that sucks! Can I have the “forbidden” foods ever again?

Most likely yes, but you’ll probably want to watch your diet and listen carefully to your body.  Alcohol seems to be a big trigger in some individuals.

51. What foods are rich in thiamine?

• Brown rice
• Pork
• Beef
• Tuna
• Oranges
• Eggs
• Liver
• Peas
• Nutritional Yeast

52.  Have you seen metronidazole toxicity in your real-life circle of friends?

Yep, twice.  One friend had a partner who took metronidazole for months, and her partner had all the classic toxicity symptoms, but no medical professional attributed the symptoms to the drug.  I told my friend what happened to me, and she gave her partner vitamin B1 and magnesium.  Three months later, she reported that her partner was “back to her old self.”

The second one was a psychologist I know.  His grandfather went to the hospital, they gave him metronidazole, and he began to having slurred speech and confusion.  Because the psychologist knew of my case, he informed the doctors to immediately stop the drug…and the symptoms vanished.  They caught it quickly and everything resolved without further issue.

This is just in my daily life.  And I’m an introvert—I don’t know a lot of people!

I hope this information has helped you. I know it’s a lot, but again, you have to be your own health care warrior here—no one else can do it for you.  If you want to learn more, please check out the blog’s other pages:

• Homepage (overview of metronidazole toxicity)
• Anxiety (focuses on this debilitating aspect of the toxicity)
• Here are the Facts (all the medical literature about this toxicity)
• Treatment (the connection between metronidazole and thiamine with links)
• YouTube: The Metronidazole Toxicity Channel
• Article on Hormones Matter: Metronidazole: The Mitochondrial Nightmare
• Article on Hormones Matter: Metronidazole Toxicity and Doctor Denial

I wish you all a speedy recovery!