Cranberry

What it is

Cranberries are small, tart red berries (Vaccinium macrocarpon) eaten fresh or dried and drunk as juice; supplement forms include capsules, tablets and powders [1][2]. The compounds studied most are proanthocyanidins (PACs), measured in milligrams per serving [1].

How it might work

Proposed mechanism: PACs interfere with hair-like structures (fimbriae) on E. coli, the bacterium behind most UTIs, so it sticks less easily to the cells lining the bladder [1]. Reviews also describe gut bacteria breaking PACs down into active metabolites that may add to the effect [3].

What the research says

Preventing repeat infections. The 2023 Cochrane review pooled 50 randomised trials with 8,857 participants; across 26 trials (6,211 people) cranberry products reduced symptomatic, culture-verified UTIs by about 30% (risk ratio 0.70, 95% CI 0.58 to 0.84), with high heterogeneity between studies (I2 = 69%) [1]. In women with recurrent UTIs the reduction was about a quarter (risk ratio 0.74, 95% CI 0.55 to 0.99; 8 trials, 1,555 women) [1]. A 2021 meta-analysis of 23 trials (3,979 people) found similar results overall (risk ratio 0.70) and in women (risk ratio 0.68), and a trial sequential analysis suggested the effect was conclusive [4]. A 2025 network meta-analysis of 50 trials (10,495 people) found a 28% reduction versus placebo (risk ratio 0.72) with no excess adverse events [5].

Individual trials. In a 24-week trial, 373 women with a recent UTI drank 240 mL of a cranberry beverage or placebo daily: 39 versus 67 clinical UTI episodes (incidence rate ratio 0.61), about one episode prevented per 3.2 woman-years [6]. A 2024 trial in 160 women found 240 mg of PACs daily roughly halved UTI episodes over 12 months (incidence rate ratio 0.49) [7]. A 2025 trial in 150 women found 500 mg of whole-fruit powder daily cut culture-confirmed UTIs by 52% over 6 months (relative risk 0.48) [2]. A 2015 trial in 182 women found whole-fruit powder reduced UTI diagnoses (10.8% versus 25.8%) [8].

Children and procedures. In the Cochrane review, children had about half the risk (risk ratio 0.46; 5 trials, 504 children) and people whose infection risk rose after a medical procedure about half the risk (risk ratio 0.47; 6 trials, 1,434 people) [1]. A 2021 meta-analysis in children found cranberry reduced recurrence versus placebo (risk ratio 0.48) and matched antibiotics (risk ratio 0.92) [9]; a 2024 review of 23 studies (3,335 children) found cranberry lowered the odds of symptomatic UTIs during prophylaxis, while no prophylaxis option reduced kidney scarring [10]. A 2015 trial in 160 women found cranberry capsules cut UTIs after gynaecological surgery (19% versus 38%; odds ratio 0.38) [11]; a 2020 trial in 210 women found no significant difference after pelvic-floor surgery (12.4% versus 20.0%) [12].

Juice, doses and antibiotic use. A 2024 network meta-analysis of 20 trials (3,091 people) estimated cranberry juice lowered UTI rates by 54% versus no treatment and 27% versus a placebo drink, and reduced antibiotic use by 49-59% [13]. A 2024 meta-analysis of 10 trials suggested doses of at least 36 mg of PACs a day reduced UTI risk by 18% while lower doses did not, and only 12-24 weeks of use was linked to fewer infections [14]. In the Cochrane review it was unclear whether juice and tablets differ, and no PAC dose-response could be shown [1].

Groups that did not benefit. Cochrane subgroups found no clear reduction in older people in care homes (risk ratio 0.93; 3 trials, 1,489 people), pregnant women (risk ratio 1.06; 3 trials, 765 women), or people with bladders that do not empty fully (risk ratio 0.97; 3 trials, 464 people) [1]. A 185-woman nursing-home trial also found no difference in bacteriuria plus pyuria (29.1% versus 29.0%) or symptomatic UTIs (10 versus 12 episodes) over a year [15].

Treating an infection. A 2023 Cochrane review on treating UTIs found no randomised trial that met its standards, so there is no good evidence that cranberry clears an existing infection [16]. A 2021 feasibility study in 46 women showed a general-practice trial could be run, but it did not test whether symptoms improved [17].

Doses used in studies

Studies used 240 mL of cranberry juice or juice drink daily [6]; capsules providing 240 mg of PACs daily for 12 months [7]; two capsules (72 mg of PACs) daily for a year [15]; and whole-fruit powder at 500 mg daily for 6 months [2][8]. After gynaecological surgery, 2 cranberry juice capsules twice a day (equivalent to two 8-ounce servings of juice) were given for 6 weeks [11]. A 2024 meta-analysis suggested at least 36 mg of PACs a day and 12-24 weeks of use as the range linked to fewer UTIs, while the Cochrane review could not confirm a dose-response [14][1].

Safety and interactions

Common side effects. In 10 trials (2,166 people), gastrointestinal side effects were about as common with cranberry products as with placebo (risk ratio 1.33, 95% CI 1.00 to 1.77), so cranberry probably makes little difference [1]. A 2024 trial in 160 women reported no adverse events [7].

Upper doses and toxicity. The trials did not establish a toxic dose, and a safety review found no serious risks from cranberry ingredients consumed properly in supplements [18][1].

Interactions. Case reports have linked cranberry to stronger warfarin effects, but a randomised trial in 30 patients on stable warfarin found no effect of 240 mL of cranberry juice daily on warfarin levels in blood, with one small INR change judged unlikely to be clinically important [19]. A safety review found moderate intakes (240-480 mL/day) were not associated with interactions, and that reported interactions mainly involved very large intakes (1-2 L/day of juice or 3,000 mg/day of extract) or people who were seriously ill [18]. A 2021 systematic review still lists cranberry among foods reported to interact with warfarin, so people taking warfarin or other blood thinners should ask their doctor [20].

Pregnancy and breastfeeding. Three trials in 765 pregnant women found no reduction in UTIs [1]; no data on breastfeeding were found in the studies read.

Kidney and stone risks. Data are contradictory: a small randomised trial in 20 men found cranberry juice lowered oxalate excretion and the relative saturation of calcium oxalate in urine [21], while the safety review reports conflicting data, with some reports suggesting cranberry is linked to a reduced risk of kidney stones [18].

Caveats and open questions

The pooled 30% reduction comes with high heterogeneity (I2 = 69%), and several subgroups - care-home residents, pregnant women and people with bladder-emptying problems - show no benefit [1]. It is unclear whether juice, tablets and powders differ, and no PAC dose-response has been shown [1]. Some evidence has industry ties: a 2017 meta-analysis was partly funded by Ocean Spray [22] and the 2025 whole-fruit powder trial by a supplement company [2]. Earlier reviews disagreed partly because they weighted different populations differently, which is why the recurrent-UTI group matters most [23]. No completed trial has tested cranberry for treating an active infection [16].