tuneTypical Dose
2 g daily dissolved in water, taken as a single dose
Supplement
D-Mannose
D-mannose (C₆H₁₂O₆, C-2 epimer of glucose)
Evidence TierDWADA NOT PROHIBITED
watchEffect Window
The MERIT trial assessed outcomes over 6 months. No significant benefit was observed at any time point during follow-up.
check_circleCompliance
WADA NOT PROHIBITED
Overview
Clinical Summary
D-Mannose is a simple sugar marketed for UTI prevention through competitive bacterial anti-adhesion, but the best placebo-controlled evidence does not support a significant preventive effect.
D-mannose has been widely promoted for preventing recurrent urinary tract infections based on a plausible anti-adhesion mechanism and one early positive open-label trial. However, the largest and most rigorous placebo-controlled study (the MERIT trial, 598 women, 2024) found no significant difference in UTI recurrence between D-mannose 2 g daily and placebo over 6 months. An updated 2025 meta-analysis also remained non-significant and highly heterogeneous. D-mannose is well tolerated and safe, but the efficacy evidence is insufficient to recommend it as an effective UTI prevention strategy.
D-mannose is a simple sugar excreted in urine that can competitively bind FimH adhesin on type 1 fimbriae of uropathogenic E. coli, theoretically reducing bacterial adhesion to urinary epithelial cells. This mechanism is demonstrated in vitro but has not translated to significant clinical UTI prevention in well-controlled human trials.
Outcomes
What This Is Expected To Influence
Primary Outcomes
- D-mannose 2 g daily did not significantly reduce medically attended UTI recurrence versus placebo in the largest RCT (MERIT trial, 598 women, 6 months)
Secondary Outcomes
- Two 2025 meta-analyses confirmed no significant pooled benefit for D-mannose vs placebo or active comparators
- D-mannose is well tolerated with a safety profile similar to placebo
Safety
Contraindications and Interactions
Contraindications
- Active UTI with systemic features
- Congenital disorders of glycosylation
Side effects
- Bloating
- Loose stools or diarrhea
- Nausea
Interactions
- Diabetes medications
Avoid if
- Active UTI symptoms are present and need medical evaluation
- Known congenital disorder of glycosylation
Evidence
Study-level References
d-mannose-SRC-001Double-blind, placebo-controlled, two-group randomized clinical trial
Sourceopen_in_newHayward G, Mort S, Hay AD, et al. d-Mannose for Prevention of Recurrent Urinary Tract Infection Among Women: A Randomized Clinical Trial. JAMA Intern Med. 2024;184(6):619-628.
Population: Women aged 18 and older with recurrent UTI (two or more episodes in the past 6 months or three or more in the past 12 months) recruited from 99 primary care centers in the UK (n=598)
Dose protocol: 2 g D-mannose daily vs matched placebo for 6 months in 598 women across 99 UK primary care centers.
Key findings: No significant difference in medically attended UTI recurrence (51.0% vs 55.7%, risk difference -5%, 95% CI -13% to 3%, p=0.26). No benefit for time to first UTI, total episodes, or antibiotic use.
Notes: The definitive study for D-mannose. Large, well-powered, double-blind, placebo-controlled, primary care setting. Negative result effectively settles the question of efficacy at 2 g daily.
Paper content
The MERIT trial is the largest and most rigorous RCT of D-mannose for UTI prevention to date. In 598 women with recurrent UTI across 99 UK primary care centers, 2 g of D-mannose daily for 6 months did not significantly reduce the proportion experiencing medically attended clinically suspected UTI compared with placebo (51.0% vs 55.7%, risk difference -5%, 95% CI -13% to 3%, p=0.26). No significant differences were observed in time to first UTI, total UTI episodes, or antibiotic use. D-mannose was well tolerated with no significant increase in adverse events. The authors concluded that D-mannose should not be recommended to prevent future episodes of medically attended UTI in women with recurrent UTI in primary care.
d-mannose-SRC-002Systematic review and meta-analysis of randomized controlled trials
Sourceopen_in_newKrishna MM, Joseph M, Pereira V, Nizami A, Ezenna C, Sreemathy LS. 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.
Population: Adult women with recurrent UTI from 4 included RCTs (n=890, D-mannose n=447)
Dose protocol: Meta-analysis of 4 RCTs (890 participants) with D-mannose at various doses, most commonly 2 g daily.
Key findings: Pooled RR 0.44 (95% CI 0.18-1.11, p=0.082). Not statistically significant. Very high heterogeneity (I-squared 90%).
Notes: The high heterogeneity is driven by inclusion of both blinded and unblinded trials. When the best-designed studies dominate, the signal disappears.
Paper content
This updated meta-analysis pooled 4 RCTs with 890 participants and found that D-mannose prophylaxis did not significantly reduce the risk of recurrent UTI in adult women (RR 0.44, 95% CI 0.18-1.11, p=0.082). Heterogeneity was very high (I-squared 90%), likely driven by differences in blinding, comparator arms, and population characteristics across the included trials. Adverse events were not significantly increased (RR 2.19, 95% CI 0.68-7.05, p=0.190). The authors concluded that the results do not confirm the efficacy of D-mannose for UTI prophylaxis in adult women but noted that a beneficial effect cannot be entirely ruled out. They called for additional high-quality placebo-controlled trials.
d-mannose-SRC-003Open-label, three-arm randomized clinical trial
Sourceopen_in_newKranjčec B, Papeš D, Altarac S. d-mannose powder for prophylaxis of recurrent urinary tract infections in women: a randomized clinical trial. World J Urol. 2014;32(1):79-84.
Population: Women with acute UTI and history of recurrent UTI, no significant comorbidities (n=308)
Dose protocol: 2 g D-mannose daily vs nitrofurantoin 50 mg daily vs no prophylaxis for 6 months in 308 women. Open-label, no placebo.
Key findings: 14.6% UTI recurrence with D-mannose vs 60.8% with no prophylaxis (p<0.001). Appeared strongly positive but was open-label without placebo.
Notes: The study that generated initial enthusiasm. Its positive result is almost certainly inflated by lack of blinding and absence of a placebo arm. The MERIT trial, which corrected these flaws, did not replicate the finding.
Paper content
This early RCT found that 2 g daily D-mannose reduced recurrent UTI to 14.6% over 6 months compared with 60.8% in the no-prophylaxis arm. Nitrofurantoin showed a similar reduction (20.4%). Both active groups were significantly better than no prophylaxis (p<0.001). D-mannose had fewer side effects than nitrofurantoin. However, the study was open-label with no placebo arm, which introduces substantial performance and detection bias. The no-prophylaxis arm does not control for placebo effect. This study generated initial enthusiasm for D-mannose but its methodological limitations are significant and the results were not confirmed by the later, larger, placebo-controlled MERIT trial.