HIgh doses are supposed to have that effect, it's called bowel tolerance and shows that you've saturated your tissues with the C, which is what you want.
Of course, you can spread out the dosage, as that guy did who cured his gum disease by taking 5 grams with every meal for a total of 15,000 grams/day.
I take Twinlab full flush niacin, 1000 mg. 2-3 times a day.