Quercetin is a phytoestrogen and flavonoid found in fruits, vegetables, and grains; it exhibits antiviral, anti-inflammatory, antihypertensive, anti-allergic, immunomodulatory, and neuromodulatory activities. Quercetin inhibits reverse transcriptase activity and suppresses replication of hepatitis C virus. In vivo, quercetin increases energy expenditure and decreases release of inflammatory cytokines. Clinically, this compound decreases blood pressure. In animal models of OVA-induced allergy, quercetin decreases levels of IL-4 and Th2 cytokines and increases levels of IFN-γ and Th1 cytokines. Quercetin also inhibits calcineurin and monoamine oxidase (MAO).