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. Hello. Thank you for all the time and effort you put into this website. It’s been so helpful and it’s a relief to not feel alone when you’re suffering like this. Three days ago, I started taking d mannose ( waterfall sweet cures brand) and it aggravated my lingering UTI symptoms until it was like I was dealing with a full blown attack of cystitis! I had been able too old my bladder for about 8-9 hours ( which meant I could sleep) but suddenly I was having to go EVERY HOUR ( I couldn’t sleep or go anything). I kept taking more of the d mannose and couldn’t believe what was happening to me. It made no sense. Reading this post has given me an answer (the potentiality of d mannose irritating the bladder lining) . What confuses me is Sweet cures ( have you any experience with this brand, might I ask?) had always been my go to brand. Could it be a bad batch? Or have they changed their formulation? The only thing different is that they’ve come out with smaller (500mg as opposed to 1,000mg ) pills and that has suited me just fine as I have difficulty with the larger pills ( I used to chew them because they were too large to swallow). Please wish me well in my recovery as I’ve decided to leave the d mannose for now but I have lingering symptoms of irritation in my tract… Any advice you can offer me would be most welcome. Thank you so much for your time!

    1. Anastasia Visotsky

      HI Hannah, see how you feel without D-Mannose. It will be out of your system within ~4 hours, so if symptoms greatly subside then we can blame them on D-Mannose. You can ask the company and see what they think, but it could be that you developed an intolerance with time or, perhaps, some other bacteria, not E.coli caused your symptoms and D-Mannose is best when preventing UTIs caused by that bacteria. Best wishes,

  2. Hello. I was on Harmony D-Mannose for a few weeks and I started getting really potent smelling urine! I stopped taking it. Not sure what that was about. Do you know anything about that?

    1. Anastasia Visotsky

      Hello! This is new, I haven’t heard about D-Mannose causing this type of side-effect. Normally, if you have bacteria in your urine, it could smell differently and look cloudy, but this would mean an ongoing infection not a side-effect from the powder. See if stopping the supplement clears the urine and then try again to take it and monitor the results. You can also experiment with different brands.

  3. I am a chronic and recurrent UTI patient. I just completed my 14 days of nitrofurantoin last sunday and symptoms was decreased only
    not gone properly and I just started d mannose from this sunday. Today I’m having headache….

  4. My Mom has an antiobiotic resistant e-coli UTI and I was wondering if d-mannose might help her? My concern is that she is on coumadin. Does d-mannose interact adversely with coumadin?

    1. Anastasia Visotsky

      Hi there. You can give it a try for a resistant E.coli. As to interactions: very little has been studied but since the main effect of D-Mannose attributed to the fact that it is not fully metabolized and excreted in urine, the drug interaction is probably not a major concern. I’m not a physician so double-check with your doctor! Best wishes to your mom.

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