Hey Craig. I know that Japanese Knotweed is a source of resveratrol. People who drink red wine may do so for their health.
Supplement companies don't usually use red grape skins as their source, they use the cheaper source- Japanese Knotweed.
This info may be helpful. "Some caution
should be exercised when consuming this plant because it, similar to rhubarb, contains oxalic acid, which may aggravate conditions such as rheumatism, arthritis, gout, kidney stones or hyperacidity." (From Wikipedia.)
BTW, I work in a health food store.
"I plan on living forever, so far so good!"