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.

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

  1. Can D-mannose cause bleeding? I just got over a UTI and was using antibiotics to clear it up. Once I finished with the antibiotics, I started taking cranberry tablets, probiotics and D-Mannose in powdered form in water. I had also finished my period and then two days later I started bleeding, but it doesn’t look like my regular menstrual discharge. What can be causing this bleeding?

    1. Anastasia Visotsky

      Huh! Haven’t heard that one, but, perhaps, a good idea is to get your hormones checked if it’s vaginal bleeding. Also, perhaps hemorrhoids? 🙂

  2. I started having loose stool, nothing too bad, but on the fourth night, I couldn’t sleep due to the horrible cramps I was having and still am, but not quite as much now. Now I’m very gassy, and still feeling a little bit of the cramps. I had originally read there weren’t really any side effects so I came looking and found this page. Thanks for the information!

  3. Hi! I just started a regimend of raw garden of life probiotics and d mannose. I am 14 weeks pregnant and was going to be on my third round of antiobiotics for a uti when i decided to try these supplements instead. (Mostly because the uti just kept coming back but also because the antibiotics were making me feel awful).
    Ive had no problems taking the probiotic, but i tried taking d mannose the NOW brand last night and i vomited it all up aggresively. Im not entirely sure why… maybe i drank it too fast or i was too full? But my throat now hurts terribly and im afraid to try it again even though i want too. I made sure to get the nicer brand so i wouldnt react to it. But idk… would you try it again?

    1. Anastasia Visotsky

      Dear Rachel, I’m sorry, but I can’t stress enough how important it is to treat a UTI properly when pregnant, this is a case when you can’t experiment on your own because you are not on your own :). I can’t recommend ANY other option but seeing a doctor. If you can’t stand the idea of antibiotics, talk to a naturopath who has experience working with pregnant women. I know you are looking for an answer but I’m afraid I don’t know how to proceed in your case besides seeing a doctor. Hope you understand. Best wishes!

  4. I get terrible, terrible gas. What gives?? 😭 D Mannose is finally a solution for my UTIs but the gas hurts, smells really bad, and really puts a cramp in my life when I’m fighting a UTI. 🙁

  5. Has anyone had any trouble with their feet ankles or calves swelling. I’m trying to pinpoint what is causing this problem for me thank you. Gerry

    1. Anastasia Visotsky

      Hi Gerry, yes, I heard about swelling before but again, a very strange symptom and a very rare one. Since folks take all kinds of things it might or might not be related to D-Mannose.

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