9 Main D-Mannose Side Effects And How To Avoid Them

Some say D-Mannose has practically no side-effects and it’s safe to take it indefinitely. While generally, this seems true, in many cases D-Mannose can cause some unpleasant side-effects and in some rare cases, it could be even dangerous.

Quality control

Unfortunately, the FDA does not regulate food supplements. Therefore, it’s up to a manufacturer how to make it and what to add to the powder. For example:

  • Some brands use additives, others don’t.
  • Some make D-Mannose from corn, others use birch tree juice, pineapples or cranberries.
  • Most buy D-Mannose in China and repackage in the USA.

Therefore, if you are experiencing problems with one brand, don’t give up on this supplement altogether and try another one instead (see my review of  D-Mannose brands).

Frequent D-Mannose Side-Effects

Diarrhea & Loose Stool

Simply put, if you overdose on D-Mannose you will get diarrhea. You might get loose stools or it could be very watery diarrhea.

What is the critical dose? For some, it could be three teaspoons within a day, for others – one heaped teaspoon. While unpleasant, it’s definitely not the worst side-effect and diarrhea stops as soon as D-Mannose is out of your system.

Bottom line, plan to stay close to home the first day you try D-Mannose. And if you experience diarrhea, just lower your dose next time.

GI Tract Issues

You might experience stomach pain, bloating and indigestion. Looks like even a small dose of the powder could produce this side-effect. It is hard to tell if any existing conditions or diet could be a contributing factor to this problem but many members of our Facebook group report experiencing this issue.

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 quickly disappear.

Since nowadays, most D-Mannose powder is made from corn and for some people corn could be an allergen in its own right. While corn allergy is much less common than other food allergies and is not included in the top-10 allergy list, it is becoming more prevalent. Some allergic reactions to corn include hives (light red skin bumps) or a skin rash, others may manifest in headaches and stomach aches. If you know or suspect that you might be allergic to corn, then try a brand of D-Mannose derived from pineapples and cranberries.

Unusual Side-Effect: Bladder Irritation Symptoms

Another side effect that some people report is that D-Mannose can irritate the bladder. Some users complain about symptoms similar to a urinary tract infection (UTI) when they use D-Mannose for prevention. The symptom seems to go away once you stop taking D-Mannose.

Obviously, if you are taking D-Mannose to prevent or treat a UTI, the last thing you want is to experience UTI-like symptoms as a side-effect. Some reported that switching to a different brand of D-Mannose helped to get rid of this problem, though.

Read Next: Do you really know how D-Mannose works?

Rare 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 to the powder.

If You Have SIBO

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

One of the 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.

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 and therefore aggravate or cause a yeast infection, but there is still very little clinical evidence to support this.

Unlikely 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.

Read Next: How else to prevent UTI naturally

CDG Patients’ Risks

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 (less than a thousand!), it is impossible to provide clear directions about the 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

Women who are at risk of 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.
  • Upset GI tract is one of the most reported side-effects.
  • If you develop UTI-like symptoms while taking D-Mannose for prevention, you might want to try another brand.
  • Lastly, the best way to prevent UTI among women is to maintain great vaginal health. Try a special type of probiotics. 

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.

221 thoughts on “9 Main D-Mannose Side Effects And How To Avoid Them”

  1. I’ve been using d-mannose in hopes to prevent E coli UTI along with vaginal estrogen. I’m seeing a functional medicine doctor to heal my Interstitial cystitis and she wants me to stop taking the D mannose because of fungus issues because it feeds the fungus. Your thoughts on this?

    1. Anastasia Visotsky

      Hi Gigi, good question. I’m not sure and this is the first time I hear about it as a concern. Please come back and tell us what you learn from your doctor!

  2. Sally Bayliss

    I wonder if anyone else thinks that d Mannose may cause vulval soreness and stinging?
    I know this isn’t a common side effect but I have very sensitive skin and have had difficulties with this since using it to reduce incidence of ecoli flares. Interestingly I have had more ecoli flares since taking it too.
    In response to a previous comment, I was under the impression that Now was birch based as I stopped it as I gave a birch allergy. I now use Focus but am convinced it is an irritant.
    Interested in anyone else’s experiences.

  3. Hi why do i still getting hives from NOW D-mannose Pure Powder? Are they made from corn? I have been getting hives every night since i started and i thought maybe it was just a rash but it didnt go away after couple of days.

  4. I have a friend who has been who has been was undergoing Chemo for cancer and by accident, of course, it has irritated he bladder something horrible. She is diabetic and can’t seem to get it to heal. She keeps getting UTI’s and all the doctor has done has put her on Cranberry pills and is now mentioning putting her in a Hyperberic Chamber again! Do you think this would be ok for he to try with her diabetes.

    1. Anastasia Visotsky

      Hi there, yes, if she keeps watching her glucose levels while trying it. I’ve heard mixed feedback from folks with diabetes.

  5. For UTI, a friend of ours and my wife found that berberine either by capsule or by making a tea from Oregon Grape Root Powder has been effective. I recently bought d-mannose for my wife
    (Dementia, non verbal) and her stools did become loose which is a real messy problem for me, her caregiver. I will stop giving her the mannose, but will continue with the tea.

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