Resveratrol is a naturally occurring polyphenol belonging to a class of compounds called stilbenoids (or stilbenes). Plants produce it as a defence compound in response to stress, injury and fungal attack. It is found in the skin of red grapes, in peanuts, in red wine, and in unusually high concentrations in Japanese knotweed (Polygonum cuspidatum, also called Reynoutria japonica) — which is the main commercial source for supplements.

The word "trans" refers to the molecule's geometry. Resveratrol exists in two isomeric forms — trans-resveratrol and cis-resveratrol — that share the same atoms but are arranged differently around a central double bond. Trans-resveratrol is the form that research uses and that quality supplements standardise to, because it is more stable and far better characterised. When a label simply says "resveratrol", the meaningful question is how much of it is trans.

Trans-resveratrol is one of the most studied plant polyphenols. Published research has investigated it most often in the context of the sirtuin pathway, cellular stress responses and its antioxidant chemistry, frequently in combination with NAD+ biology. As a UK food supplement it carries no authorised health claims, so the honest framing is to describe what research has explored, not what the supplement will do.

People interested in longevity most often take trans-resveratrol as part of a NAD+ routine — alongside NMN and lifestyle factors. For the rationale behind that pairing, see NMN and resveratrol and our broader longevity supplements UK guide.