D-Mannose

Tier 2 — promising · UTI prevention · Bladder health

Evidence has weakened considerably. The large MERIT trial (JAMA 2024, 598 women in UK primary care) found D-mannose did NOT significantly reduce recurrent UTIs versus placebo. Earlier small trials had suggested benefit comparable to low-dose antibiotics, but these were lower quality. It works in principle by preventing E. coli from adhering to the bladder wall. Very safe with no significant side effects — may still be worth a trial alongside cranberry extract, but is no longer first-line evidence-based prevention.

Dose: 2 g/day for prevention (note: 2024 MERIT trial found no benefit at this dose); 2 g × 3 daily at symptom onset