Cranberry juice or extracts may be helpful for urinary tract infections (UTIs) in limited populations. 
Cranberries contain compounds called proanthocyanidins that may prevent bacteria from attaching to the bladder wall, which could cause UTIs. Human studies suggest possible benefit in some populations including prostate cancer patients, but overall evidence is conflicting. Cranberry may also prevent bacteria from attaching to the stomach lining and areas in the mouth. Although lab studies suggest activity against several types of cancer cells, these properties have yet to be evaluated in human studies.
In patients who are prone to kidney stones, regular use of cranberry should be avoided as it contains oxalates, a compound found in the most common form of kidney stones