OPC is mainly present in grape seeds and skins of red grapes. OPC is available to buy commercially in the form of OPC capsules and OPC tablets. This is grape seed extract. Side effects of OPC are not yet known. Of course, as with any dietary supplement, there are exceptional cases in which some people may feel uncomfortable taking it.
OPC is the short form for oligomeric proanthocyanidins. In general, one also speaks of vitamin P. It is a herbal agent which has antioxidative and anti-inflammatory properties. This substance belongs to the group of polyphenols, but is assigned to flavanols due to its chemical structure.