im 3 months in and im starting to be completely symptom free so if I could afford it I would try to get 200 billion. I read about someone who was cured while using 500 billion a day. It took him 9 months so theres no sure why of knowing if the higher you go the faster the cure. Go with what you feel good with. If you can handle 100 billion or 200 billion then I say go for it. We need plenty of probiotics.