Resveratrol (trans-3,5,4'-trihydroxystilbene) is a substance found in the skins of certain red grapes, in peanuts, blueberries, some pines (Scots pine, eastern white pine) and the roots and stalks of Japanese knotweed (hu zhang in China) and giant knotweed. It is now being sold as a mass-produced nutritional supplement. The supplement, first sourced as ground dried red grape skins, has shifted somewhat to include certain of the knotweeds as a raw material.

Resveratrol is a polyphenol produced in plants with the help of the enzyme stilbene synthase, and which has anti-fungal properties. The mechanisms of resveratrol's apparent effects toward life extension are not fully understood, but it is believed to have longevity-enhancing properties for animals by acting as a CR-mimetic, antioxidant and optimizer of beneficial cellular apoptosis. An explanation for the French Paradox (how the French live longer and have less heart disease while consuming a high-fat diet) has also been suggested in terms of resveratrol's red grape skin form present in the red wines drunk in France.

Recent experiments have demonstrated that resveratrol significantly extends the "lifespan" of a yeast, although here lifespan is meant in the sense of extending the duration of a viable yeast culture. All higher plants have the enzyme chalcone synthase, which is very similar to stilbene synthase but does not produce resveratrol.

Resveratrol has also been seen to increase the potency of some antiretroviral drugs in vitro. Recent research at Ohio State University indicated that resveratrol inhibits the development of cardiac fibrosis .

The image shown is of trans-resveratrol. Trans-resveratrol can convert to cis-resveratrol under the influence of heat or UV irradiation. Only the trans- form is capable of activating SIRT1 in vitro; it is also the form predominately found in red wine.