It depends on what is causing the diarrhea. I've had problems with parasites (amoeba). That's not your average bacterial infection that goes away relatively fast. The only thing that worked for me was raw garlic. About 6 medium sized cloves, once a day every other day. Relieve started after a week or two, but since parasites are notorious for hanging around I needed to repeat this every second week for months to get them out and not show activity again.