9 main D-Mannose side effects and how to avoid them


Some say D-Mannose has practically no side effects and it is safe to take it indefinitely. Is it true? In this post, I’m sharing my personal experience and feedback from readers who tried D-Mannose supplement.

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Quality control

Unfortunately, FDA does not regulate food supplements. Therefore, every manufacturer  makes D-Mannose from different sources:

  • Some brands use additives, others don’t
  • Some make D-Mannose from corn, others use birch tree juice. Third might be making an artificial version of the sugar in a lab.
  • The quality of D-Mannose coming from the same producer may vary from batch to batch.

If you are experiencing problems with one brand, try another one to see if it works better for you (see my review of Top Five D-Mannose brands, 2017 that are worth spending your money on).

#1 Frequent D-Mannose side effect: diarrhea & loose stool

If you overdose on D-Mannose you will get diarrhea. I’ve learned this from my own experience and heard this many many times from others. You might get loose stools or it could be very watery diarrhea.

diarrhea is one of D-mannose side effects

What is the critical dose? For some, it could be three teaspoons within a day, for others – one heaped spoon. However, in comparison to horrible side-effects from antibiotics, diarrhea is not the worst thing. Just plan to stay close to home the first day you try D-Mannose!

Finally, if you experience diarrhea as a D-Mannose side effect, just lower your dose next time.

#2 Another side effect: GI tract issues

You might experience stomach pain, bloating and indigestion. Looks like even a small dose of the powder could produce this effect. It is hard to tell if any existing conditions or diet could be a contributing factor to this problem.

Try at your own risk, but again, you could get much worse side effects when using antibiotics. Once you stop D-Mannose, the side effects should disappear.

#3 Unusual D-Mannose side effects: bladder irritation symptoms

Another side effect that some people report is that D-Mannose can irritate the bladder. Some people complain about symptoms similar to UTI when they use D-Mannose for prevention, that goes away once they stop taking D-Mannose. Obviously, if you are taking D-Mannose to prevent or treat UTI, the last thing you want is UTI-like symptoms.

#4 Rare D-Mannose side effects: skin rash & itchiness

Some women experienced skin rash and itching (itchy scalp, red itchy skin) when taking the powder. Again, symptoms seem to subside and go away once they stop D-Mannose. It’s unclear if a certain brand (source of D-Mannose) might have something with this symptom or if it’s just personal sensitivity or overdose.

#5 Unlikely D-Mannose side effects: problems when conceiving

If you are trying to conceive you might want to be careful when you take D-Mannose. Studies show that D-Mannose could bind to sperm, therefore, preventing it from fertilizing the egg, however, in-vitro studies have so far been inconclusive and only demonstrated this effect when D-Mannose was present in unusually high concentrations. If you want to be on a safe side, avoid taking D-Mannose before “baby-making” sex or shortly after.

How else to prevent UTI naturally

Hence, D-Mannose is a great product that helped many women out there, however, try it at your own risk and remember to watch your symptoms carefully.

#6 Possible D-Mannose side effects if you have SIBO

Couple readers with SIBO pointed out that D-Mannose might aggravate SIBO symptoms.

One of chronic SIBO sufferers described her D-Mannose side effects as follows: “The pain was so severe I could hardly walk for several hours. I had so much abdominal swelling and pressure that I thought I would explode. These are all signs that I have consumed something that has fed my SIBO significantly”

D-Mannose is absorbed poorly, but it is a monosaccharide, so may be problematic for some people. Start with a small dose if you have SIBO and see how your body reacts.

#7 Low-risk D-Mannose side effect: Candida flare up

Yeasts (Candida albicans) consume organic, carbon-based compounds. They feed on sugars like glucose, fructose, and sucrose. Theoretically, mannose could be converted into glucose, but there is still very little clinical evidence to support this.

#8 Potentially high-risk D-Mannose side effects among CDG patients

Multiple genetic disorders disrupt intermediary mannose metabolism. For example, MPI-CDG and PMM2-CDG are two congenital disorders that change how our bodies produce and absorb mannose. These patients might suffer diabetic like complications if taking D-Mannose supplements.

Unfortunately, due to a small number of diagnosed patients, it is impossible to provide clear directions about signs and symptoms of these genetic disorders but you might want to study this subject a little further, especially if you have any neurological symptoms such as “diminished muscle tone, seizures, developmental disability, varying degrees of cognitive impairment, and underdevelopment of the cerebellum (cerebellar hypoplasia), which can cause problems with balance and coordination” as per RareDiseases.org.

#9 Potentially high-risk D-Mannose side effects in pregnancy with a child who inherited CDG disorder

While the frequency of MPI-CDG syndrome is unknown since in many cases these disorders go unrecognized and misdiagnosed. Such congenital disorders affect males and females in equal numbers. The exact incidence or prevalence of these disorders is the general population is unknown.

According to RareDiseases.org: “The most common type (PMM2-CDG) has been reported in more than 700 individuals. In most cases, these disorders become apparent in infancy.”

Therefore, women who are at risk for having MPI-CDG children may inadvertently cause side effects in their unborn child if taking D-Mannose while pregnant.

Things to remember:

  • D-Mannose products differ one from another, and the quality, purity, and origin may vary from brand to brand and even from a batch to a batch. Buy quality brands made in the USA
  • Stay at home since you might develop diarrhea
  • Don’t be surprised if you feel bloated
  • If you develop UTI-like symptoms while taking D-Mannose for prevention, you might want to try another brand
  • If your skin is itchy, it could be one of D-Mannose side effects
  • If you are trying to conceive, you might want to use something else to prevent UTI naturally.
  • Folks who suspect they or their unborn children might have a CDG disorder should steer clear from D-Mannose.
  • Lastly, D-Mannose is not the only “secret” to prevent UTIs. Many doctors don’t know that special probiotics can work wonders!

Please leave your reviews and share your experiences if you noticed anything unusual while taking D-Mannose. I’m tracking all responses and updating this post often. Do not use your real name or email if you’d like to protect your privacy.


  1. I have to stop. I”ve been using one that is corn based that’s in powder form and it’s from amazon. I think it’s just too much glucose and I can’t separate the d mannose from other health issues I have so I’m going to stop taking the D Mannose. I’m ready to rumble on line or on the phone. My brain can’t handle it on top of other big stuff going on. It just made toxic overload into toxic overload plus glucose. It got rid of the UTI though, a super bug.

    • Oh wow, Nancy! First of all, if it helped you with a resistant e.coli, I’m sure it was worth the side effects. Please do share more: which brand did you try and what kind of symptoms you have observed. Best wishes,

  2. Hey! I really enjoyed reading this blog and hearing about all the wonderful success stories. I have so far cured two UTI’s with D-mannose. I get them a lot…like a day or two after intercourse if I dont urinate or drink a lot of water. Well the other night I had intercourse and just could not urinate afterward…then drank coffee at work the next day, which was dumb of me but I needed it. So right now I am in the middle of a UTI 🙁 I just moved so I couldnt find my last bottle of Dmannose pills lol but I went to The Vitamin Shoppe right up the road from me and they had some. Im hoping it will work for this UTI like it has for all the others. I also need to get better at taking it daily as a preventative! I always use dmannose in conjunction with Cystex pills from the store…cystex is better than the Azo pills since it doesnt turn my urine all red or orange…Anyway, here’s to hoping this current UTI can get cured!

    • Hi Chelsea,
      Thank you for your note and for sharing your experience. Great to hear that D-Mannose has been working for you. I strongly recommend probiotics as well, especially since your UTIs are triggered by sex. Best of luck!

    • I had your same struggle with uti’s after intercourse. I started using high quality coconut oil during intercourse as a lubricant and it has changed my life!!! I very very rarely get utis anymore. Just try it and see! I use tropical traditions gold label coconut oil. Hope this helps!

  3. I tried D-Mannose yesterday for the first time. I got so light-headed and heart rate so high that I felt like I was having a heart attack. I took 1 – 500 mg pill from a company called Now. I calmed it down with Magnesium, but will never take it again. I again had symptoms this mornig. I have IC and Rheumatoid Arthritis. I had lower back pain. Symptoms are only starting to subside. Not for me!

  4. Do you know anything about kidney damage?
    – ¨When taken in excessive doses, there’s some concern that D-mannose may lead to kidney damage¨
    -¨ While it may be tempting to try D-mannose to self-treat a UTI, if the infection isn’t completely eradicated, it may spread (to the kidneys) even if the symptoms are gone¨
    – ¨D-Mannose may cause a flare in SIBO or Candida¨

    How much is too much ?
    It´s recommended dosage safe?

    • Hello Maria,
      – yes, this is a quote from WebMD. However, neither in conversations with folks who research mannosides, nor with naturopathic doctors who use it, I have not heard these concerns. Keep in mind, that in high doses even water can cause kidney damage. Just follow the instructions of the manufacturers and your doctor’s advice when taking any supplement.
      -yes, that’s why it is very important to repeat a lab test if you are experimenting with an alternative treatment to know for sure.
      -I have not seen any info to corroborate this statement. Where are you citing this from?
      -I don’t know how much is too much, I have not seen any research on this topic. Every drug or a supplement has a warning to take “recommended dose”.
      -If recommended dose would not be safe, we would know about such cases by now, I assume.
      Sure! Best of luck,

  5. Thanks for your reply.
    Quote from:
    ¨… I then went to Google and did a specific search on whether D-mannose feeds SIBO and came across this list of supplements
    from Dr. Alice Siebecker, one of the leading experts on SIBO, and indeed, there it was on the list. D-mannose is listed as a supplement that has the potential to exacerbate SIBO … ¨

  6. Hi,
    My husband has been prescribed several rounds of antibiotics including Amoxin comp, Tavanic & Cipro in the last month. None of them are helping and his UTIs keep coming back. He started taking D-mannose last friday 4 times a day + apple cider vinegar 4 times a day but again he has high CRP + nitrite in urine. Do you have any idea if D-mannose can be taken alongside antibiotics? Does it have an interactive effect with Amoxin comp (amoxicillin)? We could not find any info regarding the interaction between the two anywhere. Any feedback would be appreciated.

    • Hi Eva,
      I personally do not know about any clinically significant interactions between D-Mannose and any other drugs. Regardless, you can take D-Mannose couple hours after the antibiotics. And by all means ask your doc or a pharmacist to verify.
      Make sure he gets his prostate checked and a thorough work up of bladder and kidneys. Here is a post about UTI in men.
      Also, consider asking your doc about other supplements, especially NACs while being treated with antibiotics.
      Best of luck,

  7. Our daughter gets chronic uti’s due to an inability to fully empty her bladder (needs to catheterize). I have started using 1/2 tsp twice daily for prevention. Not sure it’s helping? It’s only good for E. coli (my understanding) so it wouldn’t work when you need Amoxil which I believe doesn’t kill E. coli. I’m noticing that she looks a bit pale and has stomach pain while on it. Anyone else notice this? I’d love to keep her off antibiotics, but so far we’ve not been able to keep uti’s away.

    • Hi Monique, I’m sorry to hear about your struggles. “I’m noticing that she looks a bit pale and has stomach pain while on it” do you mean on D-Mannose or Amoxil? Have you discussed D-Mannose with her doctor? If it’s from D-Mannose, the dose might be too high for her.
      Amoxil is prescribed against a wide range of bacteria, including E.coli. Unfortunately, with chronic UTI, especially with prolonged use of a catheter, there are more chances that the infections are caused by a combination of pathogenic bacteria.
      I would suggest that you to ask your doctor what other supplements besides D-Mannose (especially if she has stomach pain) could be tried. Best wishes,

  8. Hi I just tried D-Mannose for the first time. I have UTI’s after sex usually this one was particularly bad, I notice a feeling of speedy, tingling in my arms and feeling very hyper. I do not have any sugar issues normally very healthy. I am in good shape I work out 3x per week and I am 61 years old. I have not read any type of symptoms like mine. Do you think it is safe to take again? As I am writing this the symptoms are going away.

    • Hello! Maybe scroll through the comments, I have a feeling somebody reported something similar. In any case, D-mannose is not your regular sugar, so it is always possible to experience something unusual. We still don’t know much about how it interacts with the biochemistry of the body. I wouldn’t want to take the responsibility and to suggest that it is safe to proceed. If I were you, I would proceed with caution and check in with a doctor. Best wishes,

  9. I had wonderful relief of bladder pain and frequent urination. Unfortunately, I got a rash on my hands and chest that just worsened and was so itchy, I had to quit D-Mannose. That was with 1/2 teaspoon twice a day. I tried 1/4 teaspoon weeks later, but the rash is awful and has lasted 5 weeks. I could manage the diarrhea, but not the rash. I was sorry because it really helped my chronic bladder troubles.

  10. I am beyond happy that I found this website! It has seriously helped me in my ongoing fight to put an end to my chronically recurring UTIs. However, I am still battling them and am currently going through a really bad spout – four in two months (three of which were treated and cured with antibiotics and now on the fourth trying to beat it before having to resort to antibiotics again).

    I tried D-mannose for the first time for all these UTIs in the last two months but the infections just got too bad each time. On the second round of antibiotics, I developed severe oral thrush/yeast infection. I could barely open my mouth or move my tongue and it was painful to eat. When I went off the antibiotics it went away. So it seems to be the D-Mannose combined with antibiotics.

    Then on the third course of antibiotics (again after taking D-Mannose) I developed another oral thrush/yeast infection this time accompanied by vaginal thrush/yeast infection. The oral infection was so bad I struggled to swallow even my own salvia. It was in pockets all on the side of my tongue in the back and on the inner gums in the back.

    I went on a course of seven days on fluconazole which helped but I am still recovering from it and have small amounts left in my mouth still.

    I have to say that I never had problems with yeast infections before on antibiotics until I started trying D-Mannose.

    Also this time around I am suffering from the severe bloating and potentially the irritated bladder (or the irritated bladder is just a sign of the UTI getting worse) from the D-Mannose. That said- I have always had problems with my stomach which I am still working on figuring out. So there could be an underlying cause and issue with my gut bacteria that has always been present. I was very interested to read in this article about SIBO and will be following up to see if maybe that’s something I have.

    I bought the D-mannose brand you suggested (from Bulk Supplements) and have started taking a probiotic (the repHresh one you also suggested). So I hope that they will help me prevent UTIs once I’m out of this bad spell.

    A point of interest you may like to know is that recurring UTI’s are a problem for not only me, but both my sisters, my mother and even her mother, my grandmother! I have confirmed with my doctor that mine are all Ecoli.

    Looking forward to working with you to help put an end to it all! This is the best website I’ve been on to help so thank you for all you’re doing. Keep it up!


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