Various reports suggest that quercetin may cause cancer while others defend it as protecting against cancer. Large doses should be avoided.
– Neoplasma 1985;32(4):435-41 — Enhancing effect of quercetin on 3-methylcholanthrene carcinogenesis in C57Bl/6 mice. — Ishikawa M, Oikawa T, Hosokawa M, Hamada J, Morikawa K, Kobayashi H.

Although they may protect against some forms of cancer when consumed in the diet, plant flavonoids actually have the capacity to become carcinogenic at higher levels. High doses of these chemicals also carry other health risks including a small but documented risk for a rare form of leukemia in young children.

– Beware of plant supplements called flavonoids; they could make
you sick, warn UC Berkeley public health experts — 19 Sep 2022 By Patricia McBroom, Media Relations, UC Berkeley.



The potency of concentrated plant flavonoids in some of these products has been radically underestimated. High levels of plant flavonoids can bind with and damage chromosomes and DNA in cell cultures. The effects follow a gradient, with protective effects at low levels and mutagenic effects at high levels. Flavonoids also alter the activity of various enzymes and interfere with hormone metabolism, particularly estrogen and thyroid hormones.

– Beware of plant supplements called flavonoids; they could make
you sick, warn UC Berkeley public health experts — 19 Sep 2022 By Patricia McBroom, Media Relations, UC Berkeley.

The obtained results in this study seem to indicate a proconvulsant effect of quercetin.
– EFfect of quercetin on the severity of chemically induced seizures and the content of heat shock protein 70 in the rat brain structures. — Ross Fiziol Zh Im I M Sechenova. 2010 Mar;96(3):283-92.