Cranberry

A preventive, not a treatment. The right form is a capsule standardized to ~36 mg A-type PACs rather than sugary juice, and the expectations should be set honestly; it lowers the odds of the next UTI, it does not clear one you already have.

Moderate and honestly a bit mixed, which is normal for a food-derived supplement. The strongest, most consistent signal is for reducing recurrent UTIs in people prone to them, particularly women with a history of repeat infections; pooled analyses lean positive when the product actually delivers a standardized PAC dose. A lot of the disappointing older trials used underdosed or poorly characterized products (or plain juice), which muddied the picture and is a big reason the field looks noisier than it should. The mechanism, anti-adhesion against P-fimbriated (mannose-resistant) uropathogenic E. coli, is well characterized in the lab and gives the clinical story a plausible backbone. Evidence for anything beyond urinary prevention (the general antioxidant claims) is real at the polyphenol level but much softer in terms of hard clinical outcomes.

Cranberry is a food, so the safety margin is wide and it is generally very well tolerated. The most common complaints are mild stomach upset and, especially with large juice volumes, loose stools; the sugar and acid load of juice is its own downside. There is a long-standing caution about warfarin (a blood thinner); cranberry has been reported to increase its effect in some cases, so if you take warfarin, loop in your doctor first. People prone to calcium-oxalate kidney stones sometimes worry about the oxalate content of cranberry, so heavy chronic use there is worth a conversation with a clinician. The big honest caveat is not toxicity, it is scope; if you already have an active UTI (burning, urgency, fever, blood), cranberry is not the answer and you need proper medical treatment, usually antibiotics. General educational info, not medical advice.

Cranberry is native to North America, where Indigenous peoples used the tart berry as food, dye, and a folk remedy long before it became a supermarket staple. The idea that it helps the urinary tract is old folk wisdom, originally chalked up to making urine more acidic; that acidification theory was later largely set aside once researchers identified the proanthocyanidins and the anti-adhesion mechanism as the real story. Over the last few decades the product evolved from sweetened juice cocktail into standardized PAC capsules, and the science matured alongside it as people realized dose and standardization, not just 'drinking cranberry', were what mattered.

Cranberry has one of the most recognizable reputations in the supplement aisle; almost everyone has heard 'drink cranberry juice for a UTI'. The catch is that the popular version of that advice is half wrong, because it frames cranberry as a treatment and pushes sugary juice. Among people who actually read the evidence, the respected form is a standardized PAC capsule used as prevention for recurrent UTIs, and expectations are kept modest and honest. It sits in the sweet spot of being genuinely useful for a specific job while being badly oversold for everything else.