Metronidazole toxicity

Metronidazole: The New Mitochondrial Nightmare

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When “Rare” Happens to You

On June 13, 2015, I lost the ability to walk and speak. These symptoms came on suddenly, and were accompanied by hand tremors, shortness of breath, weakness, difficulty concentrating, and dizziness. My mother drove me to the ER, but despite my deteriorating condition, I was confident the problem had a simple solution.

I’d been taking the antibiotic, metronidazole (Flagyl), for c diff (a gut infection). When my symptoms abruptly manifested, I looked the drug up online and, sure enough, all of my symptoms were listed as side effects of the medication. So my mother and I thought this would be easy, that the trip to the ER was a mere “technicality” for me to be put on an alternative antibiotic.

When it comes to having an adverse drug reaction, I would learn the hard way that things are never easy. What followed were six weeks where I could not care for myself. While a few symptoms diminished after discontinuing the medication, others randomly popped up to take the stage, this jumble of problems that didn’t seem to connect to one another:

  • Difficulty swallowing
  • Frequent urination
  • Constipation
  • Asthma-like respiratory issues
  • Complete loss of appetite (twenty pound weight loss)
  • Inability to stand up straight
  • Difficulty walking
  • Shortness of breath when talking
  • Chest pressure
  • Heart palpitations
  • Face flushing
  • Dry mouth
  • Cough
  • Headache
  • Pressure at the back of the head
  • Neck pain and stiffness
  • Constant adrenaline rushes
  • Anxiety
  • Depression
  • Crying spells
  • Insomnia
  • Extreme fatigue

I was the medical version of a Picasso painting. Nonetheless, there was one connection between these symptoms; they’re listed as side effects of metronidazole.

The Google Patient

During those first two months, I went from the patient who sees her doctor once or twice a year, to the compulsive consumer, calling several times a week, setting up appointments, and being put through the ringer of medical exams.

In total, I saw eight general practitioners, including my primary care physician, and almost every specialist known to medicine: a cardiologist, an immunologist, a pulmonologist, an ENT doctor, a psychiatrist, and a psychologist. There were tests, from multiple CT scans to X-rays, EKGs, an upper GI, an echocardiogram, a heart monitor, a laryngoscopy, several lung function tests, and about 30 vials of blood taken.

I insisted the cause of my symptoms was the metronidazole, but no one listened. After two months and no answers, my primary care physician handed down the diagnosis of depression and an anxiety disorder. That was the moment I lost faith in the medical community.

So I did the thing that doctors hate—I Googled. A lot. Medical literature is a language all its own—a new version of Pig Latin, MD edition—and I didn’t know what to search for, what the magical keywords were to unlock the “prize.”

Eventually, I ran across another group of people suffering from an adverse drug reaction—the floxies.  This group of patients had suffered an adverse reaction to another type of antibiotics called fluoroquinolones and, as I read their stories, I was horrified how their experiences mirrored my own, including their doctors usually dismissing their claims about the drugs. There were numerous blogs, YouTube videos, local media coverage, books and medical literature about their condition.  Fluoroquinolone antibiotics can directly damage mitochondrial DNA (the energy source of our cells), and people who suffer from this can become permanently disabled or even die. The effects are systemic, with certain regions of the body like the tendons, the heart, and the brain especially affected.

They called it “getting floxed,” and said they suffered from “fluoroquinolone toxicity.”  Reading this phrase, I plugged the words “metronidazole toxicity” into Google.  The answer I’d been searching for flashed on the screen.  What I had, it had a name:

Metronidazole-induced Central Nervous System Toxicity

If you lose the ability to walk and speak while taking metronidazole, there’s a 93% chance lesions have formed on the back of your brain, specifically the cerebellum, followed closely by the brain stem and then the basal ganglia. The effects cause motor control issues, seizures and an “altered mental state.”

From Patient to Blogger

Upon finding numerous pieces of medical literature to back up my claim about metronidazole toxicity, I presented the information to my primary care physician. When I tried to set up another appointment a short time later, she banned me from her clinic. It took a meeting with her supervisor and the clinic’s Risk Management to receive the proper diagnoses on my records—cerebellar dysfunction and altered mental state.

My ban from the clinic was never retracted.

At this point, it became clear that, not only did the medical community not have a way to treat an adverse drug reaction like metronidazole toxicity, they refused to even acknowledge it existed.

Nonetheless, the diagnoses didn’t fully explain my symptoms. There were others, like heart palpitations (including irregular blood pressure), constipation, dry mouth, loss of appetite, difficulty swallowing, and breathing issues that just didn’t match with cerebellar dysfunction.

Over nine months, my condition had greatly improved. I was able to work and enjoy social activities again, but some lingering symptoms would still randomly “flare up,” either due to over-exerting myself, an illness, allergies, or for no reason at all. I used to be an avid biker and that was no longer possible.  There were times, when a flare up would be too great, that I’d end up back in bed.

I decided to take the medical literature on metronidazole and create an online blog for others who might need answers. In addition, I started a support group on Facebook for metronidazole victims; when it began, there were three of us.  A year and a half later, there’s over a hundred, and counting.

Each of us have different issues, but almost all of them fall into four categories:

  • Cerebellar dysfunction (dysfunction of the cerebellum)
  • Autonomic dysfunction (dysfunction of the brain stem)
  • Altered Mental State (neuropsychiatric issues)
  • Polyneuropathy (damage to the nerves throughout the body)

Despite metronidazole’s ability to damage the brain stem, there’s little medical literature connecting metronidazole to autonomic dysfunction. The autonomic nervous system controls all the “automatic” operations of the body, like heart rate, breathing and digestion. As I listened to various stories from other patients that matched my own about uncontrollable heart palpitations, irregular blood pressure, dry mouth (dysfunction of the salivary glands), digestive issues, asthma-like respiratory issues, irregular sleep patterns, swallowing issues and the like…it became clear that this was the final puzzle piece to the metronidazole mystery.

Some patients have recovered as well as I have or better; others are disabled and housebound.  Almost everyone has flare up’s, months or years after taking the drug. Some people have full relapses and worsening symptoms long after they took metronidazole.

So the question keeps being asked—why? Why are these symptoms still here so far out from taking this drug?

Metronidazole and Thiamine

It was November of 2017 that I had the biggest flare up in two years. I had begun a second job on the weekends to get some extra cash for the holidays. My symptoms had remained steady for well over a year at that point, with only mild flare up’s. By the second weekend of work, my condition worsened, with symptoms that I thought were long-gone returning in full force. Heart palpitations, weakness in my legs, difficulty breathing, dizziness, brain fog, chest pressure, and even the anxiety came roaring back. On top of these, two new symptoms developed—pain in my hands and feet, and ringing in my ears. I had to quit the seasonable job, and, with the exception of going to my full-time work, I stayed mostly in bed for weeks.

At this time, I happened upon Dr. Lonsdale and Dr. Marrs’ new medical textbook, “Thiamine Deficiency Disease, Dysautonomia, and High Calorie Malnutrition.”  The title caught my eye because I vaguely recalled, through my metronidazole research, the word “thiamine” had popped up multiple times. So I bought the book.

Everything I had experienced was listed within its pages. Thiamine (aka vitamin B1) is essential for oxidative metabolism. It is the gatekeeper of our mitochondria and, without it, the cells cannot properly convert food into fuel. In addition to this, without thiamine, oxygen cannot be properly utilized, causing our cells to—for lack of a better word—suffocate.

This suffocation (called “pseudohypoxia”) leads to our autonomic nervous system to activate its “fight-or-flight” response, which causes extreme anxiety, insomnia, emotional instability, a heightened sensitivity to stimuli, and an overall lowering of our stress threshold. In addition to these symptoms, there is a paradoxical one; the body is not designed to run on its fight-or-flight response for days or weeks on end. This over-use of the body’s energy reserves results in extreme fatigue.

Thiamine is found all over the body, but there are places where its use is concentrated, the brain being the most crucial, followed by the heart and our nerves. When there’s a deficiency, dysfunction typically hits the back of the brain the hardest—specifically the cerebellum and brain stem. Lack of thiamine causes:

  • Cerebellar Dysfunction
  • Autonomic Dysfunction
  • Altered Mental State
  • Polyneuropathy

After reading Dr. Lonsdale and Dr. Marrs’ textbook, I went back to all the medical literature I had pulled about metronidazole toxicity (and then some). It turns out, metronidazole and thiamine are antagonists; the drug inhibits thiamine from being absorbed into the body, which can plummet the victim into deficiency. The chemical structure of metronidazole is similar to that of the third ring within thiamine’s chemical structure; when the body mistakes metronidazole as this third ring, it turns thiamine into “thiaminase”—an inhibitor of thiamine.  This is called “thiaminase poisoning,” and it plummets the body into deficiency.

The symptoms of thiamine deficiency and metronidazole toxicity are identical.

Theoretically, the reason patients cannot recover from metronidazole toxicity adequately is because they never restore their thiamine after discontinuing the drug. The deficiency is too great to recover from by simply eating thiamine-rich foods; it requires high-dose supplementation over months to resolve the underlying problem. Therefore, victims of this toxicity are, at best, skating on the edge of this deficiency, and when a stressor enters our lives—illness, work, exercise—we exhaust the limited thiamine we have.  We plunge back into deficiency and the neurological symptoms manifest once again.

To conventional medicine, thiamine deficiency is considered a relic of the past—something that belongs in history books like scurvy—and rarely happens in the industrialized world. But there is one modern-day condition that is still being recognized by the medical community—Wernicke’s encephalopathy. This is an alcohol-induced thiamine deficiency that causes lesions to form on the back of the brain, specifically the cerebellum and brain stem.

In medical literature, metronidazole toxicity and Wernicke’s encephalopathy are constantly being compared because their symptoms and presentation of brain lesions are almost exactly the same.

Metronidazole and the Floxies

It all comes down to the mitochondria. For two years, I’ve read various stories and spoken directly with dozens of victims of metronidazole toxicity. Many times, they have commented about their symptoms being similar to that of the floxies, with several of them even stating that they’ve been “floxed.”  I’ve corrected them, explaining that metronidazole is in a different class of antibiotics and, while it causes damage to the brain, there’s no significant medical literature proving that it causes mitochondrial damage.

Nonetheless, as I’ve read numerous accounts from the fluoroquinolone community, I couldn’t help but note the similarities in our neurological symptoms.  Metronidazole victims don’t have the ruptured tendons…but the polyneuropathy and central nervous system effects (including psychiatric effects) are indistinguishable.

One website I focused on during my metronidazole toxicity research was It houses one of the largest collections of customer reviews on the internet for medications, and metronidazole/Flagyl is the most reviewed drug on the site.  It also has the 5th highest number of 1-star reviews (Cipro and Levaquin are 1st and 2nd).

I compared metronidazole and its central nervous system side effects to that of those two popular fluoroquinolone medications from reviews between 2000 and 2015, totaling the number of reviews complaining about CNS symptoms:

Reviews Metronidazole Cipro Levaquin
Total # of Reviews 3312 1828 2032
Total # 1-star Reviews 1246 1352 1432
Dizziness 733 200 246
Fatigue 471 206 144
Anxiety 556 281 229
Panic Attack 180 95 65
Depression 641 185 152
Confusion 155 53 69
Disorientation 96 20 19
Paranoia 76 26 38
Headaches/Migraines 837 263 209
Suicidal Ideation 33 47 36
Numbness 157 121 119
Burning Sensation 51 151 133
Tingling Sensation 225 130 120

If metronidazole toxicity is caused by thiamine deficiency, then this deficiency is causing mitochondrial dysfunction and possible damage. And since thiamine concentrations are highest in the brain—specifically ,the cerebellum and brain stem, which is also the highest in mitochondria—this means that metronidazole is ultimately causing the same CNS issues as the fluoroquinolones.

Essentially, people with metronidazole toxicity are getting brain-floxed.

Can Something Be Done for Victims of Metronidazole? What I Have Learned

Unlike those who suffer from fluoroquinolone toxicity, those with metronidazole toxicity might have one advantage—our mitochondria haven’t been damaged directly by the antibiotic. Because it is a thiamine deficiency that is, in theory, the true culprit in this crime, it might be possible for victims of metronidazole toxicity to have a relatively clean-cut treatment plan.

Dr. Lonsdale and Dr. Marrs explain in detail about thiamine deficiency in their textbook, including the condition’s history, its symptoms and how they’ve implemented this information into action for various patients with documented case studies. If you believe you’re suffering from thiamine deficiency, reading this text would be the first big step in your treatment plan.

Depending on your level of deficiency, you will need to decide what works best for you. To sum up, there are several versions of thiamine to pick from; thiamine mononitrate and thiamine HCL are readily available at pharmacies and health food stores. Because they are water-soluble versions of thiamine, it is difficult to overdose on them; however, if you have severe or chronic thiamine deficiency, their benefits might be limited due to their short time span in the body and their inability to penetrate the cell without a protein transporter (making the absorption a little more complex).

Other versions may only be available for purchase online, but they cut out that “middle man.”  Allithiamine is naturally derived from garlic and is a fat-soluble version of thiamine. Because it is fat-soluble, the body stores it longer and it works better on the central nervous system and nerves.  Benfotiamine is another fat-soluble version, synthetically made, and works well on nerves but not the brain.  Lipothiamine has similar effects as Allithiamine, but is synthetically made.

You must supplement magnesium with thiamine. These two nutrients go hand-in-hand; thiamine supplementation will not work without magnesium. One option is Natural Calm Magnesium Powder that dissolves in water; you can control your dose of magnesium easily. If you notice loose stools, cut back. It’s available at several health food stores like The Vitamin Shoppe and online.

As the book details, patients who are severely and/or chronically deficient might need to “megadose” on thiamine before they notice improvements. If you feel you need to megadose, it would be a good idea to be monitored by a physician. Integrative physicians are more likely to support nutritional therapy than conventional doctors. Because this is new medical knowledge, you will probably have a lot of “trial and error” before finding the right type of thiamine and dosage that helps your condition and it could take months before treatment starts to work if you have a severe or chronic case. Do not begin by megadosing, however—start small and work your way up.

Thiamine has limited side effects, but they can happen, as can allergic reactions at high doses. If you are severely deficient in thiamine, there’s a good chance you’re deficient in other nutrients and taking thiamine might make those deficiencies more apparent. You could also have a “paradoxical” effect at first, as your cells have adapted to not having adequate thiamine (this is actually a good sign, as it confirms your body is no longer well-adapted to thiamine due to deficiency).  The paradoxical effect is temporary, but if you feel uncomfortable, scale back to a smaller dose and then work up from there.

One issue that could arise with high doses of thiamine over time is an imbalance of the other B-vitamins. However, this works both ways. If you are deficient in thiamine, then taking high doses of other B-vitamins right now could further imbalance your thiamine. After speaking with patients suffering from metronidazole toxicity, one misdirection is to take high doses of vitamin B12 (some even get injections).  This seems to result in worsening of the toxicity symptoms. Eventually, you’ll want to supplement other B-vitamins to keep everything in balance, especially if you wish to megadose on thiamine for a longer duration.

Unfortunately, there is no clinical trial for me to point when it comes to metronidazole toxicity and thiamine. It is taking medical literature from one side of the spectrum and connecting it to the other side.

I started taking thiamine mononitrate about two weeks after my major flare up began, 100 mg’s.  It did nothing, so I doubled it to 200mg. After two days, I started to feel better. I switched to thiamine HCL, 300mg, after another week and, again, noticed improvement. After reaching 600mg, I switched to Allithiamine at 50mg. I had a slight “paradoxical reaction” the first day, with anxiety and shortness of breath that dissipated quickly. Now, I’m at 200mg of Allithiamine, and my flare up has gone from debilitating to mild.

I still have a long way to go, but for the first time in two and a half years, it finally feels like my health is curving in the right direction.  There is a light at the end of this very long tunnel. Just like me, if you feel you suffer from metronidazole toxicity, then there might be something you can do about it.  There might be hope in treating your symptoms. Please be advised, however, I am not a physician and this post does not constitute medical advice. It is simply what I have learned over the course of my illness. To treat your illness, you will need to educate yourself, learn everything you can, and work with a physician.

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Image credit: Pablo Picasso, Weeping Woman under creative commons license.

Erin Jensen graduated with a Bachelor's in English from the University of Kentucky in 2004, under the tutelage of authors Gurney Norman, Janet Eldred, Judith Moffett, Nikky Finney, and New York Times bestselling author Kim Edwards.

In 2005, her first fictional short story was published in Tales of the Talisman magazine, and she has since had over a hundred nonfiction articles published in Living Well 50 Plus Magazine, The Human Resource Magazine, Health & Wellness Magazine (a medical magazine for general readers), and Kentucky Doc Magazine (a medical magazine for physicians).

In addition to publications, she has also been a writing tutor at the Carnegie Center for Literacy and Learning, and is the facilitator of The Lexington Prose Group for aspiring authors.

She currently lives in her hometown of Lexington, KY.


  1. After the horrors of metronidazole toxicity, our daughter found you and started thiamine hcl. She worked her way up to 600mg hcl and for 4 years she did great, all symptoms subsiding except now and then, almost like flashbacks which would cause momentary anxiety. So 6 months ago she went down to 400mg hcl and seemed fine until late March this year, which was quite stressful for her. She had a relapse, with ataxia, hardly any sleep, etc. We started upping the hcl and now, even at 900mg of hcl, it comes and goes. She is thinking of moving to lipothiamine. We know you aren’t a doctor, but is 50mg lipothiamine a good place to start? Maybe supplementing with a little hcl? Thank you for all you share.

  2. Hi Erin, What is the dose for allithiamine and Mg you would advise for recovery from metrinidazole which has caused lack of food digestion and lack of the same energy I used to have? Thank you.

    • Hi, ZA. I have several videos and a support group with this information. Please look at the article on HM called “Exploring Metronidazole Toxicity: A Video Series,” for links to those YouTube videos (Part III is the most crucial for you). Also, you can join the FB support group–just make sure to answer the questions. There are now almost 3,000 members there who have similar experiences.

      • Thank you so much for your reply. I don’t have Facebook. Is there another way I can access the information please? Also is the HM article on this website? Thank you

        • Well, I have other articles on this site, but I do have a video series that talks about all of this at length. You can access it on the articles, “Exploring Metronidazole Toxicity: A Video Series,” on the Hormones Matter site–just look it up. And I have a blog at that discusses everything and also has links to literature and the videos.

          • Thank you. I have looked through the material but I can’t see whether allithiamine and magnésium should be taken with food or without since it is lipid-soluble. Please kidnly advise. Thank you

  3. Hi Erin, HELP! My food no longer gets digested and I am looking anorexic following 7 months after taking metrinidazole, amoxicillin and PPIs for h pylori. Seems I can no longer digest fats or any food for that matter as shown by undigested food in stools. I mean completely undigested. How much of the allithimaine and Mg should I take? Thank you.

    • Hi, ZA. I have several videos and a support group with this information. Please look at the article on HM called “Exploring Metronidazole Toxicity: A Video Series,” for links to those YouTube videos (Part III is the most crucial for you). Also, you can join the FB support group–just make sure to answer the questions. There are now almost 3,000 members there who have similar experiences.

  4. Oh my god I am so so glad I found this. I finished a course of antibiotics about a month ago now and from starting those horrible things I’ve had the worst anxiety I’ve ever experienced, intrusive thoughts and panic attacks.. feeling like my mind is racing. I’ve been taking loads of probiotics and magnesium and day by day it’s slowly getting better but it’s been the worst experience of my life. No doctor understands or won’t look into why it’s happened and keep saying it’s an anxiety flare up… I’ve never had anxiety in my life and it started the day I took those tablets.
    Reading this made me feel better but I’m so sorry everyone else has had to or is going through the same thing.

  5. Hello Erin if you’re still on this blog I have been taking the metro and cypro for about five days. I feel a bit slow even typing now. I had colitis and they never told me what kind but I no longer have blood in my stool anymore. My heart rate shot up to 165 and I went back to the er. What other drugs can I use that’s safe? Do you know? I don’t want to become a floxy. I just found your page because I’m having these stupid heart palpitations. Is it safe to stop the drugs? Please I need help

    • Jeremy, please stop metro!! I am 17 months out and still not right. It has been absolutely a terrible journey.

  6. Hi Erin, I took metrodinazol almost 2 months ago, doctors did RMI and it was fine, but I still have dizziness, brain fog and my brain works very slow. I don’t know if this could be Korsakoff’s syndrome because before the tractament I was breastfeeding my newborn. What should I do? Thanks a lot.

  7. Can polyneuropathy from Metronidazole toxicity be reversed? I currently feel some paresthesia followed by numbness in most areas of my body. It’s only been 10 days since I stopped Metronidazol gel (3 doses). I have been taking 1000 mg Thiamine HCL along with 200mg Magnesium for 6 days already.

    • Yes, it’s possible but it will have to be a mix of stopping the dysfunction and then allowing the body to heal. This could take some time, as nerves heal slowly.

      You have enzymes in your mitochondria that require thiamine to function. Without thiamine, those enzymes can’t work well, and one of them is responsible for fatty acid metabolism–fatty acid creates the coating around the nerves. As that enzyme becomes dysfunctional due to low thiamine, the coating around the nerves becomes damaged due to lack of fatty acids to sustain itself. This damage is the neuropathy.

      Thiamine treatment can work quickly to stop dysfunction and halt more damage, but once cells are dead, they are dead. Thiamine can’t do anything about that, but the body can heal from damage. It might just take time and, depending on the level of damage, it might not be a full recovery. Everyone is different. But we’ve seen people recover fully from this, so we know it is possible.

  8. Erin, how long did you detachment feeling last. I’m going on 6 months now trying to recover. They put me on Wellbutrin and I somewhat improved but still far from normal. Will it get better
    Thanks chrissy

  9. Wow! I am so glad I found this article. I am on the verge of tears right now because the Metronidazole is still leaving my body. Thank goodness I had only taken 4 doses(of a prescribed 14) before I realized there was something seriously wrong with the way I was feeling. On day 3, I had a major panic attack (and I don’t suffer from anxiety), dizziness, confusion, acid reflux, tremors, stomach ache, heart palpitations, depressive thoughts and crying fits. It has been 24 hours since the last pill I took and although the anxiety is gone, I now feel depressed. I took a Vit B complex(that contains B1) and magnesium after reading your advice. Fingers crossed that I escaped any permanent damage and that I’m feeling like myself again soon.

    • Hi , I’m so glad I found this. I have taken 3 days of a seven day course of metronidazole 400mg, for a rot canal infection. I have never felt such an extreme feeling of depression and anxiety. I really still feel terrified to go to sleep tonight. I couldn’t stop crying and have felt this awful feeling of not seeing the point in anything , I am so scared that this won’t go. I’m not taking any more tablets. Not sure what to do though,

  10. Three years ago I was treated with Metrnaidazole. It nearly killed me and 2 other people. I had nausea and dizziness from day one. By day two I was weak and sure I had something worse than the parasites I was attempting to eradicate. On day three I could not stand up and was having what I describe as lucid blackouts with stroke like symptoms. I went to the ER. T her doctor did an ultrasound of my stomach (which was dumb), tried to have a nurse give me IM Atvian to “relax” all while I’m having a blackout in front of him. I had to call a friend to come to the ER and Addie them I was not a drug using hypochondriac.
    They home telling me only that the symptoms were unlikely to be from the medication, but to stop it “just in case”. Two days later I was driving home from work and blacked out. I hit a sweet vintage car that was in front of me. Of course, no one knew I was having “rare” neurological symptoms from the medication.
    I too did my research and finally found two journal articles that documented my symptoms. My neurologist later told me he’d heard of this reaction, but only when someone was on a high dose for a long period of time. Lucky me!
    This stuff is horrible. A doc recently tried to prescribe it. I reminded him I was allergic. He then tried to prescribe a drug that is closely related. I refused and changed doctors.
    Since then, I’ve heard many tales of the horrible effects this has for SOME people.
    Thank you for the article.

  11. Hi Dr Derrick,

    I am Amit from Mumbai, India.
    I am facing the same situation as Erin above due to Metronidazole toxicity. But in India, I have Benfotiamine. What shud b my dosing regimen? 400 mg per day? for how many months? pl guide me. I wud b so grateful to you.

  12. I want to thank everyone for posting. This article saved my life. Toxicity had to the point of not walking or talking, I was hallucinating, in altered states, seizures and ALL of the symptoms listed here. I am one year out and still have bad flare ups that scare the living crap out me and my husband and family. I take thaimine and magnesium and it helped drastically Improve my symptoms. I am so sorry to all who have ever dealt with this. Everyday can feel like a mystery, life with toxicity debilitating. I take the fat soluble thiamine and magnesium. Please do addition homework on magnesium absorption and get regular blood work done on your vitamins Bs, D and thaimine. It’s crucial. Thank you all so much.
    If you are new and feel you may be experiencing metronidazole toxicity please discontinue the dose and seek help ASAP before it damages you more. Get your blood work done immediately (note: it may not reflect thaimine deficiency at first get it done a week later if you still have symptoms after discontinued use of metronidazole)
    Get your brain scanned for lesions.
    Take thaimine and magnesium (it can’t hurt you)
    Good luck and may we all be healed at some point.

  13. I literally am in shock as I’m reading this artical and the comments and I do not know any of the people . I was given this drug, metronidazole along with cephalexin for a serious case of colitis. As I’m reading I realize that the exact symptoms that are being discussed are the very same ones that I have been complaining with to my husband. I know my body and I know something is not right. Please help me by telling me what I need to do first. Thank you

    • Hello I am so sorry to hear this is happening to you. You are not alone. I have been dealing with metronidazole toxicity symptoms for over a year. I am not a doctor but I strongly suggest discontinuation. I too listened to my doctor who told me to finish my dose and I got worse and worse. I went to the emergency room and had a seizure after they gave me my metronidazole dose via IV and they still did not link it. I took it for ten days, To the point of loosing the ability to walk. I am a year out of my toxicity and I still have flare ups. I take the fat soluble thiamine and still have flare ups but over the last year they have started to be less frequent. Please please right away get a blood test to check thiamine asap! That will help narrow down if the metronidazole is causing thiamine imbalances. Many of us suffer years out from this toxicity so please by all means help yourself. Feel free to reach out. I would never wish this on anyone.

  14. Could you not argue that if you had a bad parasite infection metronizaole would be worth the trade off of taking it.

    • Hi, John. Do you mean for me or for you? I didn’t have a parasite infection; I had c diff, which is still a bad infection but other antibiotics can take care of it. Metronidazole can actually damage the brain, so…brain damage vs. parasite?–when another less dangerous antibiotic could cure it? So I would say no, unless the infection is chronic, life-threatening and other antibiotics won’t work. Metronidazole should be a last-resort drug in my opinion.

  15. Does anyone know of an alternative antibiotic to use for treating gut issues caused by parasite bacteria?

      • I’m so thankful for this article <3 I was prescribed flagyl 3 times in the span of 4 months and each time my health was deteriorating rapidly, I went to the ER not long after starting the 3 round bc I couldn’t remember my own name or where I was. It wasn’t helpful that I was treated with a sedative and told it was just anxiety, but this post made me realize that I’m not crazy about flagyl messing with my mind. I haven’t taken any thiamine yet but I’ll come back to this post when I do. Again I really appreciate the information and how you’ve complied so many resources on this issue

  16. Dear Erin,
    I really thank you for your very helpful article and blog, and thank u everyone for sharing ur experiences as it felt a great relief to find out that im not alone while i think i am spending the worst days i cud never imagine, actually i had no specific physical symptoms except some panic attacks & sleeping problems, most of my symptoms were mental, terrible anxiety, then it turns to depression, suicidal thoughts, different kind of phobias!, ocd thoughts, weird emotional swings, & feeling disconnected sometimes, n these symptoms jus switch their place every day! N i never had them ever before i started taking metronidazole for 2 weeks for lung infection(Which i dunno if its even used for that kind of infection!!) While i was so desperate searching for what made me this kind of person i saw your blog & it was such a great great relief to know that i wasnt goin crazy! I will start trying thiamine and mg supplements, & i hope it will help us all feel better as we did before this horrible medicine, thanks again

  17. Dear Erin,
    thank you for your engagement in the floxi society. Your comment on floxiehope showed me that i am not only beeing floxed.
    i took cipro and metronidazol in Mai 2017. i just developed cns symptoms like ataxia, dizziness, depression, hallucination, brainfog, depresonalisation, later in the monts fatigue and just a short time little tendon problems in the feet. While i am on metro i feel the cns Symptoms.
    i am always wondering why i just developed cns problems and not like other floxies tendon, muscles and pns problems….

    I will try thiamin in high doses. I hope, its the answer….

  18. Hi Erin

    Thank you so much for your research on metronidazole intoxication and how to cure it!!
    Im also a victim of this awful drug. I have one question. Now Im on 100mg allithiamine but I would like
    to dose it higher. How long can these pardoxical reactions last, do you have an idea?
    Do I have to take allithiamine together with magnesiumor can I take magnesium separately?
    Thank you!


    • Hello. I found out I had h pylori and was prescribed 1000 mgs of both metronidazole and clymothrin (spelled wrong) for 2 weeks. I’ve had aches in my armpit/ upper chest, aches behind my ears, stiff neck and brain fog followed by severe anxiety ever since. I keep telling the doctors something isn’t right but all my tests keep coming back good. One doctor mentioned the antibiotics maybe giving me tendinitis. Any advice on what to do going forward??

  19. What would be best in theory to prevent metronidazole induced thiamin deficiency: Take high dose thiamin during the days you also take metronidazole? Or take high dose thiamin after the metronidazole is out of your body, after your quit the metro.
    Since metronidazole inhibits Thiamin uptake, taking thiamin during the days you take metro would be useless?
    After I found your article I ordered 200 tablets of 100 mg thiamin. I took 5 pills during the days I took metronidazole and all of my symptoms disappeared: Intestinal cramps, anxiety and derealization gone. I think you are on to something!

    • I don’t think it would hurt anything to take thiamine (don’t forget to also take magnesium) while taking metronidazole. It’s not 100% clear what all the drug does to thiamine, but it looks like it destroys it, so taking a lot of thiamine while taking the drug could potentially prevent or decrease the chance of becoming deficient if you give yourself more of the vitamin than the drug can destroy. And your symptoms disappearing while you’re still on the drug–that’s wonderful! That’s a very good sign that maybe the drug can still be used by just adding 2 simple supplements to the regimen. Then we’d have a good antibiotic that can help destroy infections but none of the serious side effects that have harmed so many people.

  20. For me, metronidazole is always different everytime i take it… i prefer the cream because i feel no side effects at all but in the beginning with the pills i just had a horrible migraine…. the worst one ive ever had and it was everytime i was taking the first course of doses… i actually stopped my pills early because i couldn’t handle the headaches anymore… now when i take the pills i feel dizzy and bad anxiety, heart palpitations… im even having trouble sleeping at night.. i can’t go to sleep until like 5 or 6am… it’s my 5th day so I have 2 more days left of pills left I just hope my insomnia won’t last

  21. Check out the anti-folate property of metronidazole. That may be the piece missing that is key to helping you recover. I came across this in my research on my MTHFR 677 mutation. Most people have some level of mutation in the folate cycle, you may have one of the more severe ones.

    Folate and Thiamine swap places so that phosphorylated thiamine is released from the cell and folate goes in.

    “Low doses of methotrexate can deplete folate stores and cause side-effects that are similar to folate deficiency. Both high-folate diets and supplemental folic acid may help reduce the toxic side-effects of low-dose methotrexate without decreasing its effectiveness.[8][9] Anyone taking low-dose methotrexate for the health problems listed above should consult with a physician about the need for a folic acid supplement. ”

    For B6 use Pyroxidol 5′ Phosphate aka P5P form. Large doses up to 100 mg are used to treat elevated homocysteine.

    I had some similar symptoms and am taking 300 mg allithiamine daily. I also take multiple doses of magnesium glycinate and rda level doses of manganese which can be dangerous in higher doses.

  22. I was just prescribed the flagyl cipro cocktail. After reading about the side effects and long term problems I am uncertain that I even want to take these meds.

  23. Thank you for this❤
    I was floxed 4 times and given Flagyl with it. I’ve had 80% of the black box side effects. I was always able to work, sometimes in pain, but my mental state was fine, so I went on. One year ago I was having a diverticulitis attack, the doctor insisted Flagyl with Bactrim since I can’t take Cipro. I begged her to find something else, but she said there wasn’t anything that would work. All HELL broke loose, this was my 6th time and last time taking Flagyl. I had the normal side effects of severe headache, vomiting and no appetite, but what was horrible this time is I had extreme anxiety, heart palpatations, depression and suicidal thoughts, my flowing symptoms came back with a vengence, but after a year, I still get anxiety, which before this I never had, only with meds I’ve had anxiety, but after stopping it would go away. Now, after a year, I still have bouts of anxiety weekly, extreme fatigue, constant dizzy feeling, my muscle weakness is getting worse, all over body pain, probably from being floxed, but something scary happened Dec. 30th, I don’t go out much because of my condition, but I had passes to a concert and I went, I was on my feet for hours at a time, I was wearing a slight wedge heal, which makes you use your muscles in you legs more, but the end of the night, going back to my room, I had to be helped back because my legs stopped working, they were lilke noodles, it was the weirdest felling, it was from the middle of my thighs down to my feet. When I went to use the bathroom I tried to wall and fell flat on my face, I had to crawl. I do have two torn meniscus in both knees, but this was my whole legs not working. The next night while lying in bed, I bet my legs up to slip them under the cover and got an excruciating pain in the tendons behind your knees, I stood up to stretch them out, the pain started to go away but they were weird weak noodles again, my legs weren’t working right again. I had to hold on to anything to make my way to the bathroom. For about a week, my legs were very weak, but I could walk, and had much pain in both knees, which I think may be the torn miniscus, and falling on them again when my legs gave out. Has this happened to anyone else? I feel if I exert my muscles at all, they become weak instead of strong. I want to strengthen my body, but I can’t, this is so frustrating. I don’t remember what it feels like to feel good, I pray for that day. I’m on my way to join your Facebook page. Thank you so much. B-1 and garlic for me, I can’t wait to see if this helps my brain. Oh, and I did have an MRI on my brain, and they said no lesions, I hope this is correct, and I can hopefully heal from the Flagyl, but the Fluoroquinolones are another battle. Just typing this is making my eyes weird and blurry.

    • Sorry for everything you’ve gone through, Cindy. I know a lot of people who have had issues with both metronidazole and fluoroquinolones (often prescribed together). I can’t account for the pain in your legs, as that sounds like a floxie-issue, but metronidazole affects the brain first and foremost, and it sounds like your difficulty walking is what I’ve gotten when I have a bad metro-flare up. The lesions from metronidazole toxicity disappear soon after taking the drug, but there’s a poor correlation between those lesions disappearing and resolution of symptoms. I’d definitely suggest, as one patient to another, of taking high doses of vitamin B1 and also get yourself some magnesium (don’t forget the magnesium, this won’t work without it!). It’ll take time–don’t expect to take it one day and be better the next–I’ve been doing this since November, and I feel so much better, but it’s a slow process. Good luck!

      • Thanks Erin, I take my magnesium everyday, I just started B-1 yesterday. Did you have dizziness and an out of it feeling? This last Flagyl really did me in. I’ll update when I start to feel better.

        • Oh, yes–the “detached” feeling lingered for a long time but it got better. The dizziness didn’t hit me as hard as others I know with metronidazole toxicity, but to put this into perspective, metronidazole has the highest complaints about dizziness on than any other drug. So you’re definitely not alone.

  24. I had a reaction to flagyl and cipro, I believe and it lasted for 8 years. It was a cascade of problems. A downward spiral of hell. Nad therapy helped me. Nad is a molecule being investigated as the principal component of aging itself. Please check out some helpful info:

    A site to get nadtherapy:

    My actual story in one of the most popular podcasts on health and biohacking:

    The upcoming conference on Nad:

    My nonprofit on NAD and addiction, brain health and longevity research.

  25. Erin
    Thanks you for sharing your journey and for never giving up and pushing until you founds answers. We clearly have so much to learn about medications and my hope is that people like you who bravely go “From Patient to Blogger” (and I would add “and leader”) will continue to lead the way. And that more and more doctors will read blogs like this and learn that they have much to learn too.

    I’m familiar with the adverse effects of fluoroquinolones, having first learned about them on this wonderful Hormones Matters site when I read an article by Lisa Bloomquist. I learned even more when I interviewed her so I could share this important info with my community of anxious women.

    I was not aware of these issues with Metronidazole and appreciate all your work and the thiamine work of Chandler Marrs and Derrick Lonsdale. And will be sharing this article widely.

    I’d love to hear if you came across similar issues with other classes of antibiotics such as cephalosporins (like Keflex)?

    • Hi, Trudy. I don’t know about Keflex; my medical knowledge doesn’t go far beyond metronidazole and fluoroquinolones. I can say that I haven’t heard anything about Keflex, but that doesn’t mean there’s nothing there.

      Thank you for the nice comments. I think it’s time there was more awareness about the dangers of metronidazole and all adverse drug reactions; if doctors implemented appropriate care, it’s estimated that we could cut down ADRs by half. Just looking at people who die from ADRs annually in the US (roughly 100,000, although that number is very outdated), that means we might be able to save 50,000 patients.

      Lisa is wonderful; I adore her. She’s extremely kind, down-to-earth, and very knowledgeable. She’s taken her suffering and turned it into something positive.

      I’ve spoken to Dr. Marrs and she has been such a great support. I highly recommend her and Dr. Lonsdale’s textbook for anyone who believes they could be suffering from thiamine deficiency. It’s very well-detailed and offers a variety of case studies and how those patients were treated with thiamine and magnesium.

      Again, thank you for the comment. It’s very appreciated. –Erin

  26. I have been suffering for over 2 n half years from this toxicity and would love to talk to others and the author if possible is that possible?

  27. I am 11 years FLUOROQUINOLONE toxicity, connecting 2014. I recently quit taking b complex a few months ago as I learned B6 can aggrevate PolyN and I simply was sick of supplements. Im drained. My heart and soul. I too lost MD faith. I have severe autonomic and poly neuropathy from FQ’s. For 2 months, I have become very weak to walk, so weak my mouth muscles are affected, my mouth hangs open. I immediately started back b complex and cq10. It’s helping. My doctor thinks the weakness is severe polyN and of course, autonomic. I also took flagy given for digestive issues from fq’s by gastro. Double dip.
    Thanks for listening. I’m lost and weak.

    • For fluoroquinolones, I’d suggest looking at Lisa Bloomquist’s lovely website, There is so much medical literature and patient stories, including things they did to recover.

      It could be metronidazole toxicity only or fluoroquinolone toxicity only…it might be both. It’s hard to tell, as both can cause the issues you’re describing. I’ve heard the B6, at high doses for long periods of time, can cause neuropathy. Is there any way to take other B-vitamins and avoid that single one? I’m not a doctor, but if you’re concerned about that one vitamin, maybe it’s something to consider.

      Also, if you believe you’re suffering from thiamine deficiency, then that alone can imbalance other nutrients (as the example of B12 in the article). It gets complicated.

      Good luck! I hope you feel better.

    • Thank you, I’ve looked at it–great summary of side effects. Metronidazole is the most reviewed antibiotic on that site, I do believe.

      • Hi Erin, would it be possible if I could talk to you? I have gotten much worse after recent infections thank you Melissa

  28. For those readers that desire more reading on thiamin and its part in disease go to Amazon books and type in Derrick Lonsdale and Chandler Marrs

    • Hi Dr. Lonsdale,

      What test to measure thiamine levels do you recommend is the most accurate? On the Mayo Clinic website, it suggests measuring thiamine in whole blood is now the best test. I recently had this test taken and my thiamine was well within range. Is the Erythrocyte Transketolase test (only available in London) still the most accurate?

      Thank you for your wonderful research!

  29. Excellent article. Thank you for sharing your story. Your story will help many others. I wish you good health.

    I attribute my lifelong health issues to a chronic thiamine deficiency. I now avoid all antibiotic therapy as much as possible. I will never take fluoroquinolones, thanks to articles like yours.

    • Thank you! Yes, this experience has certainly made me wary of all drugs, especially antibiotics. No fluoroquinolones for me, either–they should only be given for life-threatening situations where other antibiotics have failed.

      • Dear Erin. Did u develope depression or issues on how u felt mentally. I’ve been struggle for 3 months now and I’m need advice. Nobody can seem to help me

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