Solgar® Quercetin Complex includes the important bioflavonoid Quercetin in a synergistic formula with Ester-C® Plus to provide unique antioxidants as well as immune health support.* Quercetin is found in onions and other foods. It possesses antioxidant properties which help to fight free radicals.* Ester-C® Plus provides a unique, pH neutral (non-acidic), form of vitamin C that is gentle on the stomach. Ester-C® Plus offers the additional benefits of incorporating acerola berry, citrus bioflavonoids, rutin and rose hips. This formula also features bromelain, a natural enzyme derived from pineapple.