Mason Natural Plant Based Quercetin Complex 625 mg - Immunity Booster, Healthy Inflammatory Response, Potent Antioxidant, 60 Tablets Quercetin is a plant pigment belonging to a group of plant compounds called flavonoids, which are present in grains, fruits, and vegetables. As an antioxidant, it may bind to and neutralize free radicals which are known to cause cellular damage. As an anti-inflammatory agent, it may help reduce swelling and inflammation in the body. Individuals who take Quercetin supplements are looking for an immunity booster, inflammation reducer, and improved general health.