Little is known about the effects of an overdose with quercetin. It is not even clear if an overdose is possible or how much quercetin would result in an overdose. If you think you or someone else may have overdosed on any medication or supplement, including quercetin, please seek medical attention immediately.
It is not known how to best treat a quercetin overdose (if, indeed, an overdose is even possible), since it is not known exactly what effects an overdose might cause. Therefore, treatment (if necessary) will involve supportive care, which consists of treating the symptoms that occur as a result of the overdose.
Again, it is important that you seek medical attention immediately if you believe that you may have overdosed on quercetin.