Properties, Pharmacological Activities and Toxicities of Quercetin

Abstract

Quercetin is a natural polyphenolic flavonoid copiously found in fruits, onions, shallots, herbs, teas, red wines, etc. By adding sugar moieties into quercetin backbone, derivatives of quercetin, like enzymatically modified isoquercitrin (EMIQ), hydroxyethylrutosides (HERs), quercetin-4′-O-β-D-glucoside, etc. are produced. Quercetin exhibits many activities beneficial for health and well-being, for instance, anti-inflammatory, antioxidant, anti-viral, anti-allergy, and anti-cancer activities.  Recently, commercial quercetin products were available for both therapeutic and dietary supplement purposes. Nevertheless, quercetin was proved to interact with other medications when used together as in combination, or unintentionally from food supplement ingestion. Quercetin might interfere by pharmacodynamic and pharmacokinetic interactions, with either increase or decrease effects of other medications. Moreover, quercetin could cause adverse effects with high dose usages. Fortunately, the recommended quercetin is 1,000 mg/kg body weight orally per day, for at most 12 weeks. Even if at this dose, quercetin causes no harm in animal studies, the long-term effects were largely unknown. Careful usage of quercetin should be practiced, especially with other medication concurrently intake.