The medical doctors that used mega vitamin C used the cheapest stuff and it worked, but it was lot. They also said that is a person is severely ill, that sometime that person can tolerate 100,000 mg orally before they reached bowel intolerance, since so much of the vitamin C was being consumed in the gut to fight bad pathogens. The sicker you are the more you can tolerate. Also the more toxins you have the more you can take before reaching bowel intolerance. In any case, vitamin C is non-toxic at any dose and the worst that can happen in the case of oral vitamin C is bowel intolerance.