One of the most popular uses of cranberry juice is for the home remedy treatment of urinary tract infections (UTI). It has been verified clinically and in research that cranberry juice does have a positive effect in preventing UTIs. However, it appears less likely that cranberry juice can cure a UTI once it has started. From the National Institutes of Health:
People used to think that cranberry worked for urinary tract infections
by making the urine acidic and, therefore, unlikely to support the growth of
bacteria. But researchers don’t believe this explanation any more. They now
think that some of the chemicals in cranberries keep bacteria from sticking to
the cells that line the urinary tract where they can multiply. Cranberry,
however, does not seem to have the ability to release bacteria which are already
stuck to these cells. This may explain why cranberry is possibly effective in
preventing urinary tract infections, but possibly ineffective in treating
Cranberry juice appears to have other positive effects as a preventative. Since it contains salicylic acid, which is an ingredient in aspirin, it can have positive effects on the heart. However, if you have an allergy to aspirin, you may need to avoid drinking cranberry juice.
One misconception is that cranberry juice can help to break up or cure kidney stones. This does not appear to be the case.
Cranberry juice and cranberry extracts contain a large amount of a
chemical called oxalate. In fact, there is some evidence that some cranberry
extract tablets can boost the level of oxalate in the urine by as much as 43%.
Since kidney stones are made primarily from oxalate combined with calcium,
healthcare providers worry that cranberry might increase the risk of kidney
stones. If you have a history of kidney stones, avoid taking cranberry extract
products or drinking a lot of cranberry juice. [emphasis added]
Cranberry juice can also slow clotting of the blood. Since many popular blood-thinners do the same (such as Coumadin or warfarin), cranberry juice should not be consumed while you are currently taking a blood-thinner.