Benefits
Urinary tract health
A Cochrane review of 50 trials found cranberry products probably lowered symptomatic, culture-confirmed urinary tract infections in women with repeat infections (8 trials, 1,555 women, risk ratio 0.74). It found little or no benefit in older people in care homes, in pregnancy, or with bladder-emptying problems, and no clear difference from preventive antibiotics.
Urinary tract health in children
In the same Cochrane review, cranberry products lowered the risk of symptomatic, culture-confirmed urinary tract infections in children (5 trials, 504 children, risk ratio 0.46). A child with urinary symptoms needs medical evaluation, and cranberry should only be used alongside a clinician's advice.
Less antibiotic use
A network meta-analysis of 20 randomized trials (3,091 people) found cranberry juice linked to a 27% lower rate of urinary tract infections than a placebo drink and a 49% lower rate of antibiotic use, based on six studies for antibiotics. The authors rated the certainty of this evidence as moderate to low.
Mechanism of action
Anti-adhesion in the urinary tract
Cranberry proanthocyanidins (PACs) block the attachment of P-fimbriated E. coli to the cells lining the bladder in laboratory studies. Bacteria that cannot attach are more easily flushed out with urine. This explanation comes from lab work and has not been confirmed directly in people.
Clinical trials
Double-blind, randomized, placebo-controlled trial of 2 cranberry capsules a day (72 mg proanthocyanidins in total) for 1 year in 21 nursing homes (Juthani-Mehta et al. 2016, JAMA)
185 women aged 65 or older (mean age 86).
No difference in the primary outcome, bacteria plus white cells in urine (29.1% versus 29.0%, OR 1.01). Symptomatic UTIs (10 versus 12 episodes), deaths, hospital admissions and antibiotic use for suspected UTI did not differ significantly. The result applies to nursing home residents, not to younger women with repeat infections.
Double-blind randomized trial of standardized cranberry proanthocyanidin extract, 2 x 18.5 mg/day versus 2 x 1 mg/day, for 24 weeks (Babar et al. 2021, BMC Urol)
145 healthy women with 2 or more UTIs in 6 months or 3 or more in 12 months.
The primary outcome was not met: the high dose gave a non-significant 24% reduction in symptomatic UTIs versus the low dose (incidence rate ratio 0.76, 95% CI 0.51 to 1.11). A post-hoc subgroup of 97 women with fewer than 5 infections in the prior year showed a significant reduction. No major side effects. Two authors were employees of the extract supplier.
Double-blind, placebo-controlled trial of 8 oz of 27% cranberry juice twice daily for up to 6 months (Barbosa-Cesnik et al. 2011, Clin Infect Dis)
319 college women presenting with an acute UTI.
Primary outcome negative: a second UTI occurred in 20.0% on cranberry juice versus 14.0% on placebo juice, with no meaningful difference in urinary symptoms. Overall recurrence (16.9%) was lower than the 30% the study was designed around.
Randomized, placebo-controlled, double-blind trial of 125 mL cranberry juice or placebo drink at bedtime for 24 weeks (Takahashi et al. 2013, J Infect Chemother)
Outpatients aged 20 to 79 with repeated UTIs.
A benefit was seen only in a subgroup: in women aged 50 or older, UTI relapse occurred in 29.1% on cranberry juice versus 49.2% on placebo (p=0.04). The abstract does not report a significant result for the whole study group.
Prospective, uncontrolled exploratory study of a supplement containing cranberry extract, pumpkin seed extract, vitamin C and vitamin B2 for 6 months (Jeitler et al. 2022, J Integr Complement Med)
23 women with recurrent uncomplicated UTIs.
Reported UTIs fell from 2.2 in the 6 months before to 0.5 during the 6 months of use, and antibiotic courses also fell. Intestinal microbiota did not change. With no control group and a multi-ingredient product, this cannot show that cranberry caused the change.
Systematic review of 2 randomized trials and 1 nested cohort study of cranberry supplements in pregnancy (Bolgarina et al. 2023, Cureus)
1,156 pregnant women in total.
The trials showed a tendency toward fewer UTIs but had major recruitment and retention problems, and 23% of women on juice had stomach intolerance (capsules were better tolerated). Safety data on 919 women showed no increase in malformations, bleeding or newborn complications. Efficacy in pregnancy remains unproven.