Cranberry Supplements: The PAC Number That Isn't on the Label
Educational overview — not medical advice. Cranberry is for reducing the risk of recurrent UTIs, not treating an active infection — if you have UTI symptoms, see a clinician. This statement has not been evaluated by the FDA. This product is not intended to diagnose, treat, cure, or prevent any disease.
Cranberry's active ingredient is the A-type proanthocyanidin (PAC) — it works by stopping bacteria from adhering to the urinary-tract wall, not by acidifying urine. In the 2023 Cochrane review, cranberry products reduced the risk of recurrent UTIs in women (RR 0.74, 95% CI 0.55–0.99, moderate certainty) and children (RR 0.46) (Williams 2023). The studied dose is ~36 mg A-type PAC/day (Howell 2010). The catch that defines this whole category: almost no product discloses its PAC — of 13 we track, only 4 print an actual PAC figure.
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What cranberry is (and what actually does the work)
Cranberry is marketed for "urinary tract health," and that part is grounded — but the ingredient responsible is the A-type proanthocyanidin (PAC), a class of condensed tannins concentrated in the fruit. The leading mechanism is bacterial anti-adhesion: A-type PACs interfere with the P-fimbriae that uropathogenic E. coli use to grip the bladder wall, so the bacteria are more easily flushed out (Howell 2010). What does not do the work: the total cranberry mass, the added vitamin C, or the old "acidifies your urine" story — that mechanism is largely outdated. That single fact — the dose is PAC, not total cranberry — is why the milligram or "equivalent" number on almost every label is close to meaningless.
Does it work? (the short version)
Modestly, and only for prevention. The flagship 2023 Cochrane review of cranberry products found a reduced risk of recurrent UTIs — RR 0.74 (95% CI 0.55–0.99, moderate certainty) in women and RR 0.46 in children (Williams 2023). A 2024 meta-analysis adds a dose signal: trials using ≥36 mg PAC/day cut UTI risk (RR 0.82) while trials below that dose showed no effect (Xiong 2024). But be honest about the mixed picture: a 2016 JAMA trial in nursing-home women found no effect on bacteriuria (Juthani-Mehta 2016), and the most direct dose-controlled trial was null on its primary endpoint (Babar 2021). Small and specific, not a cure.
The one-line takeaway The evidence is for a PAC dose you mostly can't verify from the bottle. Of the 13 products we track, only 4 disclose an actual PAC figure and 9 leave it a black box — so shop on disclosure first, not on the "equivalent mg" number.
The buying problem: PAC, not "equivalent mg"
Two traps. First, the label: "25,000 mg equivalent," "600 mg Pacran," and "500 mg cranberry concentrate" all describe fruit-equivalent or blend weight, not the A-type PAC that was studied (the PAC label trap). Second, the comparison: because PAC is almost never disclosed, cost per day at the studied 36 mg dose is literally incomputable for most products, so the usual value ranking breaks down (best cranberry by disclosure). The honest move is to prioritize any product that actually prints a PAC figure — the 4 that do are the only ones where "cost per active dose" means anything.
Frequently asked questions
What is the active ingredient in cranberry?
The A-type proanthocyanidin (PAC), which works by bacterial anti-adhesion (Howell 2010) — not the total cranberry mass, vitamin C, or urine acidification. That's why "equivalent mg" doesn't tell you the dose that matters.
Does cranberry actually work for UTIs?
For prevention, modestly: recurrent-UTI risk RR 0.74 in women, RR 0.46 in children (Williams 2023, moderate certainty). But it's mixed — the 2016 JAMA trial (Juthani-Mehta) and the 2021 PACCANN trial (Babar) were null. It's prevention, not treatment of an active UTI.
How much should I take?
Measured in A-type PAC: ~36 mg/day (Howell 2010). A 2024 meta-analysis found ≥36 mg/day cut risk while lower doses didn't (Xiong 2024). Most labels don't disclose PAC, so you usually can't confirm the dose.
Why is comparing products so hard?
The number that matters — A-type PAC per serving — is almost never printed. Only 4 of 13 products we track disclose a PAC figure, so a cost-per-active ranking is impossible for the rest.
Related guides
- Probiotics — strain-specific urogenital and gut evidence (with its own "which strain?" trap)
- Cranberry for UTI prevention — the honest efficacy and safety picture
- The PAC label trap — why the "equivalent mg" number isn't the dose
Sources
- Williams G, et al. "Cranberries for preventing urinary tract infections." Cochrane Database Syst Rev. 2023. PMID: 37068952
- Howell AB, et al. "Dosage effect on uropathogenic Escherichia coli anti-adhesion activity in urine following consumption of cranberry powder standardized for proanthocyanidin content." BMC Infect Dis. 2010. PMID: 20398248
- Xiong Z, et al. "Cranberry supplementation for the prevention of urinary tract infections: a meta-analysis." Front Nutr. 2024. PMID: 39668896
- Full product dataset: /cranberry/cost-by-brand.json (CC BY 4.0).