I was asked this by my older brother.  Actually, he asked me about FRS products , that have been endorsed by Lance Armstrong .  Let me say that I'm a big fan of Lance.  That being said though, I had to do this research.  The stated active ingredient is quercetin .  I did not know what that is. Although Wikipedia is not a 100% reliable site, and according to my daughter Wikipedia should not be cited as a reference, the entry on quercetin has at least 2 good references: the American Cancer Society's summary of quercetin and the FDA's summary essentially stating they have not approved any health claims about quercetin .  Quercetin is a naturally occurrring compound in many fruits.  A PubMed of "quercetin exercise" found some articles either showing no benefit and other articles showing a slight benefit.  One other point, quercetin is thought to be safe.