Cranberry juice, along with many other juices can in fact, cause diarrhea. What you should consider is exactly how much is consumed. More than a couple glasses can cause diarrhea, but more often than not, it is used to help clear the bacteria in your system that can sometimes cause diarrhea. A bit confusing, but apparently too much of anything can be harmful. Drinking too much water can be an issue! When all else fails, just remember, everything in moderation.
Taking large amounts of more than 3 or 4 liters per day of cranberry juice can cause diarrhea and other gastrointestinal symptoms. To prevent urinary infections, it is recommended to take three to six ounces of juice, twice a day of with up to 32 ounces a day for an active infection.