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D-mannose

D-mannose

Supplements. Modern nutrition.

Also called Mannose

Pinyin: gān lù táng

Spanish: Manosa

Long-term safety unknown

A simple sugar, close in makeup to glucose, sold as a powder or capsule mainly to help prevent repeat bladder infections.

Did you know? Many bladder-infection E. coli bacteria have tiny hooks, called fimbriae, that grab onto mannose sugars lining the bladder wall.

What it may help, and how strong the proof is

Infections. Lab studies show D-mannose can stop some E. coli bacteria from sticking to bladder cells. Proof that this stops infections in people is not there yet.See the research: 31 studies in people
Traditional proof
Kidneys, bladder & UTIs. Studies so far do not show that D-mannose prevents repeat bladder infections. The largest trial, a blinded, placebo-controlled study in 598 women (2024), found no clear reduction. A 2025 review of six randomized trials also found no clear benefit. An earlier open-label trial (not blinded) found results similar to the antibiotic nitrofurantoin.See the research: 27 studies in people
Unproven

Parts of the body

Kidneys & bladder, Immune system

Traditional use

Not part of an old herbal system. Cranberry juice has a long folk use for bladder health, but D-mannose as a supplement is a modern idea.

How it is classified

Herbal actions: Nutritive, Antimicrobial. Energy: neutral.

How people take it

Trials have used 2 grams a day, usually mixed in water, for up to six months. Use for longer than six months has not been well studied.

Powder and capsule.

Where to get it

D-mannose is made commercially from plant sugars and is not a meaningful food source. It is sold as powder packets, capsules and drink mixes at pharmacies, health stores and online.

Be careful

Common side effects are loose stools or diarrhea, gas and bloating, especially at higher doses. Long-term safety is not known. Its effect on blood sugar has not been well studied, so people with diabetes should check with a clinician first. Pregnancy and breastfeeding are not well studied, so avoid it unless a clinician approves.

Avoid if: pregnancy; breastfeeding; diabetes.

Mixing with other things

Works well together
Both are used for bladder health. Cranberry has many more human trials on UTI prevention, and its results are also mixed.
Use caution
Diabetes medicine (metformin, insulin, glipizide, Ozempic)
Its effect on blood sugar has not been well studied. Check with your clinician before use if you take diabetes medicines.
Worth knowing
Antibiotics (doxycycline, Cipro and similar)
Not shown to boost antibiotics. An active bladder infection needs medical care, since untreated infections can spread to the kidneys.

Adds up with others that may lower blood sugar: , , , , , , , , , , , , , and 54 more.

The honest take

Early open-label results were promising, but the largest placebo-controlled trial found no clear benefit, and a 2025 review agreed. The evidence is still thin. Repeat infections deserve a medical check, because some need antibiotics.

Sources

Each “See the research” link opens PubMed, the U.S. National Library of Medicine's index of medical studies, showing only trials and reviews done in people. The number tells you how much a use has been tested, not whether it worked. The proof rating tells you that.

Study counts checked October 2026.