D-mannose
Summary
The largest and best-run trial found no reduction in repeat urinary tract infections with 2 g/day of D-mannose in 598 women (no effect). An earlier open trial looked positive, and pooled analyses are inconsistent (grade C at best). Side effects in trials were mild.
Key facts
- 51.0% vs 55.7% had a suspected UTI over 6 months (risk difference −5%, P = 0.26; n = 583 analysed)[1]
- Recurrence 14.6% with D-mannose vs 20.4% nitrofurantoin vs 60.8% no prophylaxis (n = 308, not blinded)[2]
- Updated meta-analysis of 4 RCTs (890 women): RR 0.44, not significant, heterogeneity 90%[4]
- The large UK trial was publicly funded (NIHR) with no conflicts reported[1]
- 4 graded human outcomes on this page
- October 13, 2026
How it works
ProposedD-mannose may block bacteria from adhering to the cells lining the urinary tract by binding a site on the tip of their fimbriae; benefit was shown in animal models but not in the largest human trial.[1]
What the human research says
Human trials only, one row per outcome. The form column shows what each trial actually tested. Grades follow our evidence-grading policy.
| Outcome | Effect | Grade | Best evidence | PMID |
|---|---|---|---|---|
| Recurrent UTI (pooled RCTs) | Mixed | Grade C | Meta-analysis · n = 890 · 2025 Adult women in 4 RCTs Form: D-mannose vs placebo or no treatment · Dose: Varied by trial · Duration: Varied Recurrent UTI RR 0.44 (95% CI 0.18–1.11; P = 0.082; I² 90%); adverse events did not differ significantly. | 41195062 (opens PubMed)Source [4] |
| Recurrent UTI vs nitrofurantoin and no prophylaxis | Improved | Grade C | RCT · n = 308 · 2014 Croatian women with recurrent UTI after treatment of acute cystitis Form: D-mannose powder vs nitrofurantoin vs no prophylaxis · Dose: 2 g/day in 200 mL water (vs nitrofurantoin 50 mg/day) · Duration: 6 months Recurrence 14.6% with D-mannose, 20.4% with nitrofurantoin and 60.8% with no prophylaxis (RR 0.239 vs no prophylaxis); side effects were mild and less frequent than with nitrofurantoin. | 23633128 (opens PubMed)Source [2] |
| Recurrent UTI vs placebo or antibiotics (early studies) | Improved | Grade D | Systematic review · n = 248 · 2020 Adult women; pooled D-mannose vs placebo comparison Form: D-mannose alone or combined with other agents · Dose: Varied by study · Duration: Varied Pooled RR vs placebo 0.23 (95% CI 0.14–0.37) from small early studies; vs preventive antibiotics RR 0.39 (95% CI 0.12–1.25, not significant). | 32497610 (opens PubMed)Source [3] |
| Recurrent UTI in women in primary care | No effect | No effect | RCT · n = 583 · 2024 Women 18+ with recurrent UTI in 99 UK primary care centres (598 randomized) Form: D-mannose powder vs placebo · Dose: 2 g/day · Duration: 6 months A clinically suspected UTI occurred in 51.0% vs 55.7% (risk difference −5%, 95% CI −13% to 3%; P = 0.26); no secondary outcome differed. | 38587819 (opens PubMed)Source [1] |
Forms
| Form | Elemental % | Absorption (human data) | GI tolerance | Studied for |
|---|---|---|---|---|
| D-mannose powder | Varies[1][2] | Dissolved in water; the trials used 2 g/day.[1][2] | Mild side effects in the Croatian trial, fewer than nitrofurantoin.[2] | Recurrent UTI |
| D-mannose capsules | Varies[1][2] | Same compound in smaller units; the cited trials used powder.[1][2] | Not separately studied in the cited trials.[1][2] | Not tested in the cited trials |
Studied doses
Doses studied in human trials ranged from 2 g/day of D-mannose powder for 6 months in the UK primary care trial to the same 2 g/day dissolved in 200 mL of water for 6 months in the Croatian trial.[1][2]
Interactions
Published interactions only: each row cites a source. No row means none was found in our sources, not that a combination is safe.
None found in our sources.
Who should be careful
- People with UTI symptoms
- D-mannose did not reduce repeat infections in the largest trial and is not a substitute for assessment of a current infection.[1]
- Medicines
- No drug-interaction studies were found among the trials cited here; the product label advises consulting a physician if taking medication or living with a medical condition.[5]
Talk to your pharmacist or clinician before starting a supplement, especially if you take prescription medicines.
Where to buy D-mannose
Products from brands we partner with that contain D-mannose. Listing a product is not a claim that it works; check the amount per serving against the doses studied above, and the label for other ingredients.
- HerbsProPaid linkNow Foods, D-Mannose Powder, 6 oz1 level teaspoon (about 2 g): 2 g D-mannose, the amount used in the trialsOne-time price $30.70Shop at HerbsPro (opens in new tab)Price and label checked 2026-10-13 on the brand’s site.
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Frequently asked questions
Does D-mannose stop UTIs from coming back?
The largest double-blind trial (598 women) found no meaningful reduction in repeat UTIs with 2 g/day over 6 months.[1]
Why do some studies say D-mannose works?
Earlier positive studies were small, unblinded or non-randomized; pooled results are inconsistent.[2][3][4]
Is D-mannose safe?
It was well tolerated in trials, with mild side effects that were less common than with nitrofurantoin.[2]
Sources
- [1]d-Mannose for Prevention of Recurrent Urinary Tract Infection Among Women: A Randomized Clinical Trial.. JAMA Intern Med, 2024. RCT
- [2]D-mannose powder for prophylaxis of recurrent urinary tract infections in women: a randomized clinical trial.. World J Urol, 2014. RCT
- [3]D-mannose vs other agents for recurrent urinary tract infection prevention in adult women: a systematic review and meta-analysis.. Am J Obstet Gynecol, 2020. systematic-review
- [4]D-Mannose for prevention of recurrent urinary tract infection in adult women: An updated systematic review and meta-analysis of randomized controlled trials.. J Infect Prev, 2025. meta-analysis
- [5]Now Foods D-Mannose Powder, 6 oz: Supplement Facts and warnings (HerbsPro listing). HerbsPro, 2026. label
What changed
- Editorial evidence re-review: all trial numbers, NIHR funding and the no-conflicts statement re-checked in the MERMAIDS full text; medicines caution now cites the product label.
- Second-pass self-review: every PMID re-checked against NCBI esummary (title, year, no retraction or expression-of-concern flag), every dose, n and duration re-read against the PubMed abstract or PMC full text, grades held conservative, and interactions limited to what a cited source supports.
- First draft. Source titles and years taken from NCBI E-utilities esummary; abstracts read for every evidence row.