Japanese knotweed is the most concentrated, available, and economical source of resveratrol. It is extracted from this plant that grows wild throughout the world. Giant knotweed is not subjected to herbicides as are grown crops. Giant knotweed provides resveratrol along with emodin, a natural molecule that may induce episodes of diarrhea. To eliminate diarrhea side effects, resveratrol should be an 80-plus percent extract from giant knotweed.

Resveratrol is a polyphenol compound found in grapes, berries, peanuts, red wine, and giant knotweed. Giant knotweed is widely grown throughout Japan and is foraged as a wild edible vegetable. The root of Polygonum cuspidatum, were widely used in traditional Chinese and Japanese medicine. It is also known to be a rich source of resveratrol, which is a natural polyphenol.