E.K.
I have a chronic bladder condition. Have been dealing with UTIs since birth.
I assume, you really do mean cranberry juice. Natural, organic, etc. and NOT cranberry cocktail. Cocktail anything is just plain useless. For a UTI or anything else. Trader Joe's has the best deal on cranberry juice ($3.99 vs $8-$10 at other stores). I stock up every month.
I stock up and drink it all the time because cranberry juice works best when used preventatively. It is far less effectively when used after UTI symptoms start. Depends on the severity of the UTI I imagine. I drink it all day every day. The juice is highly concentrated. I do about 1 part CJ and 2 parts water.
So go and ahead and try it. But carefully monitor your symptoms because what you might end up doing is keeping the infection at bay vs "curing" it and if left untreated a UTI can reach the kidneys.