I have personally used quercetin and I have not seen or had any of the milder side effects reported such as headache or tingling in the arms or legs. As with most products it has not been studied in pregnancy, so that would be a possible contraindication, although there is a list of many foods that naturally contain quercetin on this site.

[link to www.webmd.com (secure)]

Quercetin is known to have antiviral properties

[link to www.ncbi.nlm.nih.gov (secure)]