It depends on how much you weigh and also your philosophy of use. My philosophy is that you are getting plenty of cysteine in your GSH, which is a safer form of cysteine than "free" cysteine. So we give our boy who weighs 100 pounds 500 mg of NAC per day. We gave our infants about 100 mg per day. I have known adults who have used up to 2 grams per day, but my philosophy would preclude me from that level of use.