Its easy, you let your body tell you how much vitamin c it needs. Build up how much you take each day, until you reach bowel tolerance, then back off a little. The main point of this article is that you can take ALOT of C when you are sick- say for example you have had blocked sinus for years, plus you also have a cold, and you are under stress, then your body can take a LOT of vitamin C before it reaches bowel tolerance. If you are healthier then you will reach bowel tolerance at a lot lower dosage. Most will need to stay on the high dose for weeks then drop to maitanence dose. And you take it in small doses throughout the day, but I find its fine to take 5 gram doses at once.