Mega-CBR is a complex of vitamin C (ascorbic acid), citrus bioflavonoids, and rutin, an non-citrus bioflavonoid. Vitamin C and bioflavonoids occur naturally together in plants, where they provide a synergistic antioxidant effect. Vitamin C is the single most commonly used vitamin supplement. It plays a major role in the formation of collagen (a structural protein in connective tissue), amino acid metabolism and hormone synthesis, and in the utilization of many nutrients, such as folic acid and iron. It is also a key factor in the body's immune system.