If you look online, it appears that probiotics have many, many positive side effects. I started taking them a couple months ago. I was taking a liquid form with 20 billion organisms per tablespoon (I took two twice a day). The first week or so, I had a lot of gas. I heard that it's because the gut is balancing, and bad bacteria are dying. Once I got that little adjustment taken care of, things worked just great.
Not sure if it helps answer anything at all, but that's my experience with probiotics!