Quercetin is a Flavonol a subtype of potent substances called flavonoids that naturally occur in plants and offer a variety of beneficial health benefits to humans. In particular, quercetin is found in rinds, young shoots, and barks of plants, and is one of the most abundant flavonoids in our diets.

Foods that commonly contain quercetin include onions, apples, grapes, berries, broccoli, citrus fruits, cherries, green tea, coffee, red wine, and capers. It is available as a dietary supplement in powder and capsule form. Typical dosages range from 500-1000 mg per day.

Quercetin as a supplement is generally well-tolerated, and side effects are uncommon at doses of 500-1000mg/day. The most common side effects are stomach upset, headache, and tingling of the arms and legs.

Quercetin is reported to be effective on treatment and prophylaxis of other SARS like coronavirus infections, as a strong antioxidant and scavenger flavonoid without any adverse events. It was shown that quercetin has the ability to chelate zinc ions and act as zinc ionophore. Therefore, quercetin could have antiviral activity against many RNA viruses. It has unique biological properties that may improve the reduction of infection risk.