A 2021 multicenter RCT (Di Pierro et al.) found quercetin phytosome 500 mg twice daily significantly reduced COVID-19 symptom duration (mean 6.7 vs 15.1 days), hospitalization rate (0% vs 8.3%), and viral clearance time vs standard of care alone. The zinc ionophore mechanism (enhancing intracellular zinc to inhibit viral RdRp) is the most likely primary antiviral pathway.

Can quercetin prevent COVID infection?

Quercetin is not a proven preventive for COVID infection. Evidence supports reduced severity and duration in mild-to-moderate cases. It does not substitute for vaccination.

What dose of quercetin was used in COVID trials?

The most cited COVID quercetin RCT used quercetin phytosome 500 mg twice daily (1,000 mg/day total) for symptomatic cases. Some prophylaxis studies used lower doses (200–400 mg/day).