Based on my experience I am convinced the knotweed is the issue. My partner and I had terrible symptoms using highly purified resveratrol (99% confimed by an independent lab etc.). Knotweed is known to have quinolones and these are known to cause tendon issues (for example Cipro makes people more susceptible to Achilles tendon ripping). Enough quinolones could be present in the 99% formulations that they are causing these problems.
I have no doubt of geo12the's reports of tendon problems, and I think that the synthetic product (ResVida) would remove any doubts about the remaining 1% of impurities. Certainly there could be something in those impurities causing a problem, although I have not had any joint or tendon issues after years of use of a 99% product.
The one question I have for geo12the is the report that knotweed contains quinolones. I have not been able to document this. I know that certain plants, such as Samento, the South American variety of Cat's Claw, have quinovic acid gylcosides, which are related to the synthetic quinolones such as Cipro. Samento has been reported to cause joint pain in some patients, as has Cipro. But I haven't seen a report of quinovic acid gylcosides in knotweed.
There is a similar-sounding substance in knotweed which is a secondary metabolite of resveratrol, 2-methoxy-6-acetyl-7-methyljuglone, which is a variety of naphthoquinone, but that is not associated with joint pain. Also emodin, found in knotweed, is an anthraquinone, but again, not associated with joint pain. Juglone has been reported to inhibit joint pain:
http://www.jimmunol....83/10/6689.longThere is a previous thread which speculates on whether emodin causes symptoms similar to quinolones:
http://www.longecity...ing-quinolones/But I don't see any reports of this in the literature. Just the opposite, emodin has been used to suppress joint inflammation:
http://www.ncbi.nlm....pubmed/23685361http://www.ncbi.nlm....pubmed/21881229It's possible that in some people, emodin may have an opposite effect. If that is true, then there is your answer. A significant portion of those 1% of impurities is going to be emodin, which is why I'm suspicious that it may be the cause for those people who have a bad reaction to a 99% product.
In short, I'm sure there is something going on, but it may not be due to a quinolone.
Edited by cudBwrong, 15 January 2014 - 08:08 PM.