- What is quercetin? Quercetin is a yellow-colored flavonoid found in plant-based foods such as capers, onions, and kale. In its natural form it is attached to sugar molecules and known as rutin (which is 49.5% quercetin), but supplements typically contain just the quercetin molecule or quercetin that has been attached to water molecules (quercetin dihydrate, which is about 90% quercetin). Interestingly, quercetin from plant-based foods has been shown to be better absorbed than quercetin from supplements. See What It Is.
- How is quercetin used? Many short-term and relatively small clinical studies have been conducted with quercetin, suggesting modest benefit in conditions such as prostatitis, insulin resistance, and rheumatoid arthritis. Quercetin may also modestly reduce blood pressure. See What It Does.
- What did CL's tests of quercetin find? Tests by ConsumerLab revealed that two products contained 12% to 14% less quercetin than claimed. Five other products were Approved, including one tested through CL's Quality Certification Program. The cost to obtain 500 mg of quercetin was found to range from just 11 cents to $1.17, depending on the product. See What CL Found, the Cost graph, and the Results table to compare amounts and costs of quercetin in products.)
- Top Picks for quercetin supplements — ConsumerLab selected two Top Picks among quercetin supplements based on quality and cost.
- How much quercetin should I take and when? Typical dosage is 500 mg taken once or twice daily. To enhance absorption, it is best to take quercetin with a meal containing fats or oils. See the ConsumerTips™ section for the dosage for specific uses.
- Safety and side effects of quercetin: Side effects of quercetin are uncommon and generally mild. However, quercetin may interact with a variety of prescription medications. For details, see Concerns and Cautions.