Quercetin is a flavonoid,  it's usually the red color in onions, grapes, wine, berries, and apples. It's a super supplement. It's pricey, can cause stomach upset on an empty stomach. Some people say it gives them a caffeine like buzz.

If you take raw buckwheat and make a tea, you can get a good dose.

It is a cancer fighter, inflammation fighter, and all around athletic performance enhancer.  I feel it, I take it only in the recommended amounts with food.