There is plenty of debate about the efficacy of most herbal supplements, but that's not my question.
I just want to know if there is a reliable/standard source of verification for the active ingredient purity of particular branded/packaged herbal supplements.
In other words, if I buy Brand X Gingko Biloba tablets, how much Gingko Biloba is in each tablet, and how much is inert fillers?
I have heard of organizations that audit the manufacturing sites of herbal supplement makers, including USP and NSF, but it appears that they do not actually test the contents of the supplements themselves.