A customized formulation of Ester-C® with bioflavonoids. Ester-C® is a patented nutritional product that contains ascorbic acid and calcium.* This formulation is non-acidic and minimally irritating to the intestines.* Esterol also provides 3 types of bioflavonoids - quercetin, rutin, and proanthocyanidins. Ester-C® vitamin C is corn-source.