Resveratrol (3,5,4'-trihydroxy-trans-stilbene) is a polyphenol and phytoalexin produced naturally by several plants when under attack by pathogens such as bacteria or fungi.

In the only positive human trial, extremely high doses (3-5 g) of resveratrol in a proprietary formulation have been necessary to significantly lower blood sugar. Despite mainstream press alleging resveratrol's anti-aging effects, there is little present scientific basis for the application of these claims to mammals (see Life-Extension section below).

Resveratrol is found in the skin of red grapes and is a constituent of red wine, but apparently not in sufficient[citation needed] amounts to explain the French Paradox. Resveratrol has also been produced by chemical synthesis or by biotechnological synthesis (metabolic engineered microorganisms) and is sold as a nutritional supplement derived primarily from Japanese knotweed.