Quercetin Side Effects and Warnings

Safety Issues

Quercetin appears to be quite safe. However, concerns have been raised that, under some circumstances, it might raise cancer risk. Quercetin "fails" a standard laboratory test called the Ames test, which is designed to identify chemicals that might be carcinogenic. Nonetheless, a bad showing on the Ames test does not definitely mean a chemical causes cancer. Most other evidence suggests that quercetin does notcause cancer and may, in fact, help prevent cancer. ¹ Still, one highly preliminary study suggests that quercetin combined with other bioflavonoids in the diet of pregnant women might increase the risk of infant leukemia. ² On this basis, pregnant women should probably avoid quercetin supplements. Maximum safe dosages for young children, nursing women, or people with serious liver or kidney disease have not been established.

Evidence suggests that use of quercetin supplements can elevate urine and blood levels of the substance homovanillic acid. ³ While this itself should be harmless, lab tests for homovanillic acid are used to diagnose a rare, dangerous condition called neuroblastoma, and for this reason, use of quercetin supplements could potentially cause a false positive diagnosis of this condition.