Quercetin is extremely common, especially apple peels. Beware of hops, as it has estrogenic effects.
Not even 100mg per liter. Purposely reduced content about 25 years ago. Wonder why?
Castrate the fucking FDA and let some of us with the skills start manufacturing iIgh Quinine Tonic Water.
I have Cinchonine (from the same Peruvian tree) but the evidence isn't really there.
However, since it's still unknown if the HIV insertions are real, look at Kudzu.