Awaiting clinical review. This entry is sourced but has not yet been signed off by a pharmacist or clinician.

D-mannose (a simple sugar)

D-mannose

D-mannose has not been shown to prevent recurrent urinary tract infections: the largest and best-run trial, of 598 women in UK primary care, found no benefit over placebo, and a Cochrane review judged the wider evidence too weak to support or refute its use. Side effects in trials were few and mild, mostly diarrhoea. Whether it helps treat an infection that has already started is untested in any reliable way, so it should not stand in for antibiotics when a clinician says you need them.

Written by

Healthy and Herbal editorial team

Updated

29 September 2026

White D-mannose powder in a glass of water with a spoon

At a glance

Last reviewed 29 September 2026

Evidence

Limited

Best for

Preventing recurrent UTIs

Typical form & use

Powder, 2 g daily

Onset

4+ weeks

Safety

Not a treatment for an active infection. No interactions in our data.

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What it's used for

Evidence is rated per use. The same ingredient can be strong for one thing and traditional for another.

Use	Evidence	What the research shows
Preventing recurrent UTIs in women	Limited	The 2024 UK trial (598 women, 99 primary care centres, 2 g daily for 6 months) found 51.0% of the D-mannose group and 55.7% of the placebo group saw a doctor or nurse for a suspected UTI (risk difference −5%, 95% CI −13% to 3%), with no difference in any secondary outcome. An earlier meta-analysis of three small studies reported a much lower relapse rate against placebo (RR 0.23), but a 2025 meta-analysis of six trials found no significant reduction (RR 0.57, 95% CI 0.29 to 1.15), and another of four trials found the same (RR 0.44, 95% CI 0.18 to 1.11) with very high heterogeneity. The Cochrane review found only very low certainty evidence.^1,2,3,4,5
Treating an active UTI	Traditional	Cochrane found one treatment-only trial among seven, and overall concluded there is little to no evidence to support or refute D-mannose for treating UTIs, with very low certainty and high risk of bias. We did not find a trial that tests D-mannose on its own against placebo for an established infection.¹

How much

Ranges below are what studies used and what supplements commonly contain. They are not a recommendation for you. Start at the low end.

Best-run trial

2 g daily for 6 months²

Powder versus matched placebo powder in women with at least 2 UTIs in 6 months or 3 in 12 months. It did not reduce suspected UTIs.

Range in trials

200 mg to 3 g daily^1,2

Cochrane describes early studies using 200 mg up to 2 to 3 g, and its included trials were too different in dose and comparator to pool. Another trial described in the UK paper used 1 g three times daily for 2 weeks, then 1 g twice daily for 22 weeks.

Duration studied

15 days to 6 months¹

This is the range across the trials Cochrane included. Long-term safety beyond 6 months was not assessed in the sources we read.

Timing · No source we read compared times of day. The UK trial gave the dose once daily as a powder.With food? · No source we read gave food guidance.How long to trial · Because the best-run trial found no benefit over 6 months, there is no evidence-based length of time at which to expect an effect.

How people take it

Powder or sachet (D-mannose alone)2 g daily (UK trial)The form tested in the largest placebo-controlled trial.

Capsule or tablet (D-mannose alone)Varies by productCochrane describes tablets and sachets as the concentrated forms trialled; the trial evidence on capsules specifically is not separated out.

Combination products with herbs or supplementsOften about 500 mg of D-mannoseCochrane included small trials of D-mannose with other ingredients, such as N-acetylcysteine and Morinda citrifolia extract. These cannot show what D-mannose itself contributes.

Safety

Who should avoid

Pregnancy and breastfeeding — not studied, the UK trial excluded these women
Symptoms of an active infection — no proof it treats one, see a clinician
Children — the sources we read covered adults only

Known interactions

No interactions in our data. Absence of a flag is not clearance.

Compare with

Head-to-head pages for the pairs people search most.

D-mannose vs Cranberry

Questions people ask

Does D-mannose prevent UTIs?

Probably not to a degree you would notice. The largest placebo-controlled trial, published in JAMA Internal Medicine in 2024, found no difference in suspected UTIs between D-mannose and placebo over 6 months. Older, smaller studies looked more positive, but Cochrane rates that evidence as very low certainty.

Can D-mannose treat a UTI I already have?

There is no reliable evidence that it can. Cochrane found little to no evidence to support or refute it for treatment. Speak to a GP or pharmacist about a suspected infection rather than relying on it.

What are the side effects of D-mannose?

Adverse events in the trials Cochrane reviewed were very few and none were serious, mostly diarrhoea and vaginal burning. One meta-analysis reported diarrhoea in 8 of 103 participants in a D-mannose-only study. In the UK trial no serious adverse events were judged related to the treatment.

Sources

Last reviewed 29 September 2026 · Next review March 2027 · How we rate evidence