Can you use cranberry juice to prevent urinary tract infections?

Possibly. There are some studies that have shown that drinking cranberry juice may reduce the risk of contracting a urinary tract infections. It should be noted, however, that taking cranberry pills did not provide a similar benefit. Additionally, cranberry juice has not been found to help treat a urinary tract infection. Bottom line: may prevent infections but does not treat infections.
Fairly effective. Well controlled placebo/cranberry juice trials have demonstrated a definite effect in preventing utis. Cranberries contain substances known as proanthocyanidins which are effective in preventing bacteria from attaching to lining cells of the bladder. These unattached bacteria get flushed out of the bladder with urination. Cranberry juice has not been shown to cure utis contrary to popular myth.