One of the bestselling herbal products of the early 1990s was an extract of the bark of French maritime pine. This substance consists of a family of chemicals known scientifically as oligomeric proanthocyanidin complexes (OPCs) or procyanidolic oligomers (PCOs). Similar (but not identical) substances are also found in grape seed. The research record is complicated by the fact that certain identically named proprietary products have consisted at different times of various proportions of these related substances.

OPCs are marketed for a wide variety of uses. As yet, however, there is no solid evidence that they are effective for any medical condition.

OPCs aren't a single chemical, but a group of closely related compounds. Several food sources contain similar chemicals: red wine, cranberries, blueberries, bilberries, tea (green and black), black currant, onions, legumes, parsley, and the herb hawthorn. However, most OPC supplements are made from either grape seed or the bark of the maritime pine. These two OPC sources lead to products that are not necessarily identical in function, although there do seem to be many similarities. In the discussion of scientific studies below, we indicate the source of the OPCs used when it is possible to do so. In some cases, however, identifying the exact product is difficult, as both grape seed and pine bark OPCs, or their combination, have at various times been sold under the same name.