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.

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, 2018 that are worth spending your money on).

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.

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, or UTI symptoms, diarrhea is not the worst thing.

Bottom line, 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.

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.

As you know, most D-Mannose out there is made from corn. One of the readers suggested that for some people corn could be an allergen.

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, the best way is to order D-Mannose that is made of pineapple and cranberries, such as these two brands. Added benefits, these products are made in the USA, not in China:

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. Some reported that switching to a different brand of D-Mannose helped them to get rid of this side-effect.

Do you really know how D-Mannose works?Learn how D-Mannose works

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.

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.

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.

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.

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.

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 type of probiotics: link to the product, & link to the post 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.

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

  1. I have had frequent UTI’s so I decided to try Harmony D mannose. I was on 1 tablet per day for a week. I became so itchy and had bruises on my body. I stopped the medication 3 days ago and the itchiness has decreased and I have not noticed any new bruising. Not a good experience.

    1. Anastasia Visotsky

      Hi Debbie, thank you for sharing your unusual side-effects, I do hear about increased skin itching from time to time, so it’s valuable to have an extra data point. The good news is, you can try many other options for supplementing your UTI prevention efforts.

  2. I developed a UTI a couple days ago and started on a liquid product called Cystex, that has Dmannose in it. It’s always worked really well if I can start it at the onset of the symptoms. I was out of town and took it with me, it kept it at bay, kind of rocky, a couple times I actually bled after utinating and had burning pain. Once I got home I immediately started on the powder form. All symptoms are gone. I’m glad to have found this page and have read to continue taking dmannose for 2-3 days after symptoms disappear. AND also glad to have read why it is recommended to drink the dmannose with a half a glass of water instead of a full one. I didn’t think it made much difference, but it does. Thank you!

  3. Confused and tired


    First of all, I’m so happy I found your website – it’s been really informative and helpful in me understanding better about utis. I’ve been suffering from recurrent uti the past 10 years but it has been at its worst in the last few months. Would get it every time I had sex, without fail. Been on countless antibiotics and just desperate to find a way out, naturally. Was told to get on low dose antibiotics but didn’t want to get on that yet and that’s when I stumbled on your site!

    So I ordered my first pack of d-mannose and this is my first week taking it once daily as a preventive measure. On the third day, I realised I had a small amount of pale green vaginal discharge, which is unusual. It wasn’t continuous but just that one time. I was wondering if this could be related to the side effect that you mentioned – Candida flare up?

    And if so, would D mannose still work for me?

    Note: went for culture test a week back and all clear, have been abstaining from sex as well.

    Hope you’ll be able to help me!

    Lost and confused

    1. Hi there,
      Oh my, sorry to hear, that’s pretty exhausting to constantly worry about UTI after sex. Well, discharge not necessarily connected with D-Mannose, especially given the small prevention amount. But, if you keep getting UTIs I’d pay more attention to vaginal health in general.
      Best wishes,

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