Extra Strength Anti-Oxidant Grape Seed Extract is a set of bioflavonoid complexes (polyphenols and flavonoids) that perform as free radical scavengers in the human body. OPC bioflavonoids were first noticed in the laboratory because they have the uncanny ability to strengthen blood vessel walls within hours after taking them. Our Grape Seed Extract is naturally extracted, so there are NO chemical or solvent residues.