Hmm interesting... I have found wide variance in how my stomach reacts to Vitamin C. I got the NOW brand with rose hips, bioflavoids, and all that jazz and couldn't tolerate it cause it was straight ascorbic acid (made my stomach rumble, etc...), then I tried Natrol "Ester-C", which is actually "calcium ascorbate" and thus has a higher PH and I tolerated it fine. I have also tried the powdered "sodium ascorbate" from Bronson research and it was the easiest cause I just mixed it with water but I think it made my BP go up cause of all the sodium. Not too much but like 5-10mm Hg... I think people just have to try the reputable brands until they find something that works. Or if you have a nutritionally savvy Dr. thats a good place to start to...