NATURAL FACTORS - NATURAL FACTORS Quercetin (500 mg - 60 veg caps) - 60 Capsule(s) - NPN: 80102203 -- Natural Factors Quercetin 500 mg provides a concentrated source of the antioxidant quercetin, a potent bioflavonoid found in certain fruits, vegetables, and herbs. Quercetin is used in herbal medicine as a blood vessel protectant and supports cardiovascular and immune health. It is an effective supplement for adults who want to protect against oxidative stress and relieve seasonal allergies.