Oligomeric proanthocyanidins (OPCs) are plant based flavonol compounds that are found in grape seeds (or pine bark). The oligomeric proanthocyanidins, as a group of distinct compounds are named after the flavonoid compounds they are derived from. This class of compounds is found at the highest concentrations in the skin and the seeds of different plant species. The simplicity of their chemical structure differentiates these versatile compounds from the more complex flavonoids they are partly derived from, the simple chemical structure of these compounds enables their rapid absorption into the blood. They are considered to be beneficial compounds for human health.
Much of the research into OPC's utilised extracts of grape seeds. Grape seed extracts can be found commercially with OPC concentrations up to about 80%. They are rich in several Proanthocyanidin B compounds, which are not found in pine bark extracts and Polyphenols are found in red wine (grape skin), peanuts and some plants.