Quercetin is a bioflavonoid and is commonly found in fruits and vegetables, especially in onions, citrus, and apples. Other sources include dark berries, grapes, olive oil, green tea and red wine which have notable amounts of quercetin. Quercetin dihydrate is derived from a flower bud called Sophora japonica and is one of the most biologically active flavonoids to support optimal health.

It is an antioxidant that is also a natural anti-histamine, and anti-inflammatory. It may expel phlegm and arrest coughing; is used for seasonal allergies and is recommended for general well-being. Quercetin has been used to support normal respiratory health as it offers support against oxidative stress. It has also been used in herbalism as a capillary/blood vessel protectant and exhibits analgesic, anti-bacterial, anti-viral and antiseptic properties.