Display Mode:

    Main content

    Health Information



    Skip to the navigation


    Proanthocyanidins-also called "OPCs" for oligomeric procyanidins or "PCOs" for procyanidolic oligomers-are a class of nutrients belonging to the flavonoid family.

    What Are Star Ratings?

    Our proprietary "Star-Rating" system was developed to help you easily understand the amount of scientific support behind each supplement in relation to a specific health condition. While there is no way to predict whether a vitamin, mineral, or herb will successfully treat or prevent associated health conditions, our unique ratings tell you how well these supplements are understood by the medical community, and whether studies have found them to be effective for other people.

    For over a decade, our team has combed through thousands of research articles published in reputable journals. To help you make educated decisions, and to better understand controversial or confusing supplements, our medical experts have digested the science into these three easy-to-follow ratings. We hope this provides you with a helpful resource to make informed decisions towards your health and well-being.

    3 Stars Reliable and relatively consistent scientific data showing a substantial health benefit.

    2 Stars Contradictory, insufficient, or preliminary studies suggesting a health benefit or minimal health benefit.

    1 Star For an herb, supported by traditional use but minimal or no scientific evidence. For a supplement, little scientific support.

    This supplement has been used in connection with the following health conditions:

    Used for Why
    3 Stars
    Chronic Venous Insufficiency
    50 to 100 mg two to three times daily
    Proanthocyanidins, a group of flavonoids, have been shown to strengthen capillaries in double-blind research.

    Proanthocyanidins (OPCs), a group of flavonoids found in pine bark, grape seed, grape skin, bilberry , cranberry , black currant, green tea , black tea, and other plants, have also been shown to strengthen capillaries in double-blind research using as little as two 50 mg tablets per day.1 In a double-blind trial using a total of 150 mg OPCs per day, French researchers reported reduced symptoms for women with CVI.2 In another French double-blind trial, supplementation with 100 mg taken three times per day resulted in benefits within four weeks.3

    2 Stars
    Capillary Fragility
    150 mg daily
    Proanthocyanidins, flavonoids extracted from grape seeds, have been shown to increase capillary strength in people with hypertension and diabetes.

    Compounds called flavonoids may help strengthen weakened capillaries. In test tube and animal studies, they have been shown to protect collagen, one of the most important components of capillary walls.4 , 5 A preliminary study found that proanthocyanidins (flavonoids extracted from grape seeds), 150 mg per day, increased capillary strength in people with hypertension and/or diabetes .6 A double-blind trial found a combination of two flavonoids (900 mg per day of diosmin and 100 mg per day hesperidin) for six weeks reduced symptoms of capillary fragility.7 Use of vitamin C with flavonoids, particularly quercetin , rutin, and hesperidin, is sometimes recommended for capillary fragility.8 Doctors often recommend 400 mg of rutin or quercetin three times per day or 1 gram of citrus flavonoids three times per day.

    2 Stars
    300 mg per day
    According to one study, grape seed extract may lower blood pressure in people with mildly elevated blood pressure.
    In a double-blind study, supplementing with 300 mg per day of grape seed extract for eight weeks resulted in a statistically significant decrease in both systolic and diastolic blood pressure in adults with prehypertension (mildly elevated blood pressure).9 In another double-blind study of people with prehypertension or mild hypertension, 300 mg per day of grape seed extract for eight weeks produced a small decrease in blood pressure that was not statistically significant compared with the placebo group.10
    2 Stars
    150 mg daily
    Proanthocyanidins, a group of flavonoids found in pine bark, grape seed, and other plant sources, may help slow the progression of diabetic retinopathy.

    Proanthocyanidins (OPCs), a group of flavonoids found in pine bark, grape seed, and other plant sources have been reported in preliminary French trials to help limit the progression of retinopathy.11 , 12 In one controlled trial, 60% of people with diabetes taking 150 mg per day of OPCs from grape seed extract had no progression of retinopathy compared to 47% of those taking a placebo.13

    2 Stars
    1.1 to 1.66 mg per 2.2 lbs (1 kg) of body weight per day during periods of high sun exposure
    Proanthocyanidins are a group of flavonoids found in pine bark, grape seed, and other plant sources that may increase the amount of ultraviolet rays necessary to cause sunburn.

    Trials have tested combinations of several antioxidants . One preliminary study found that a daily combination of beta-carotene (6 mg), lycopene (6 mg), vitamin E (15 IU), and selenium for seven weeks protected against ultraviolet light.14 However, a double-blind trial of a combination of smaller amounts of several carotenoids , vitamins C and E, selenium, and proanthocyanidins did not find significant UV protection compared with placebo.15 Similarly, in a controlled trial, a combination of selenium, copper , and vitamins was found to be ineffective.16

    Proanthocyanidins (OPCs) are a group of flavonoids found in pine bark, grape seed, and other plant sources. In a preliminary trial, volunteers were supplemented with Pycnogenol, an extract of French maritime pine bark rich in OPCs, in the amount of 1.1 mg per 2.2 pounds of body weight per day for the first four weeks, and 1.66 mg per 2.2 pounds of body weight per day for the next four weeks.17 Compared with ultraviolet sensitivity before supplementation, the lower amount of Pycnogenol was found to significantly increase the amount of ultraviolet rays necessary to cause sunburn, and the higher amount was significantly more effective than the lower amount.

    1 Star
    Pancreatic Insufficiency
    Refer to label instructions
    In a preliminary report, three patients with chronic pancreatitis who were treated with grape seed extract saw reduced frequency and intensity of abdominal pain.

    In a preliminary report, three patients with chronic pancreatitis were treated with grape seed extract in the amount of 100 mg 2-3 times per day. The frequency and intensity of abdominal pain was reduced in all three patients, and there was a resolution of vomiting in one patient.18

    1 Star
    Varicose Veins
    Refer to label instructions
    One trial found that supplementing with proanthocyanidins improved the function of leg veins in people with widespread varicose veins.

    A small, preliminary trial found that supplementation with 150 mg of proanthocyanidins per day improved the function of leg veins after a single application in people with widespread varicose veins.19 Double-blind trials are needed to determine whether extended use of proanthocyanidins can substantially improve this condition.

    How It Works

    How to Use It

    Flavonoids (proanthocyanidins and others) are a significant source of antioxidants in the average diet. Proanthocyanidins at 50-100 mg per day is considered a reasonable supplemental level by some doctors, but optimal levels remain unknown.

    Where to Find It

    Proanthocyanidins can be found in many plants, most notably pine bark, grape seed, and grape skin. However, bilberry , cranberry , black currant, green tea , black tea, and other plants also contain these flavonoids . Nutritional supplements containing proanthocyanidins extracts from various plant sources are available, alone or in combination with other nutrients, in herbal extracts, capsules, and tablets.

    Possible Deficiencies

    Flavonoids and proanthocyanidins are not classified as essential nutrients because their absence does not induce a deficiency state. However, proanthocyanidins may have many health benefits, and anyone not eating the various plants that contain them would not derive these benefits.


    Interactions with Supplements, Foods, & Other Compounds

    At the time of writing, there were no well-known supplement or food interactions with this supplement.

    Interactions with Medicines

    As of the last update, we found no reported interactions between this supplement and medicines. It is possible that unknown interactions exist. If you take medication, always discuss the potential risks and benefits of adding a new supplement with your doctor or pharmacist.
    The Drug-Nutrient Interactions table may not include every possible interaction. Taking medicines with meals, on an empty stomach, or with alcohol may influence their effects. For details, refer to the manufacturers' package information as these are not covered in this table. If you take medications, always discuss the potential risks and benefits of adding a supplement with your doctor or pharmacist.

    Side Effects

    Side Effects

    Flavonoids , in general, and proanthocyanidins, specifically, have not been associated with any consistent side effects. As they are water-soluble nutrients, excess intake is simply excreted in the urine.


    1. Dartenuc JY, Marache P, Choussat H. Resistance Capillaire en Geriatrie Etude d'un Microangioprotecteur. Bordeax Médical 1980;13:903-7 [in French].

    2. Delacroix P. Etude en Double Avengle de l'Endotelon dans l'Insuffisance Veineuse Chronique. Therapeutique, la Revue de Medicine 1981;Sept 27-28:1793-1802 [in French].

    3. Thebaut JF, Thebaut P, Vin F. Study of Endotelon in functional manifestations of peripheral venous insufficiency. Gazette Medicale 1985;92:96-100 [in French].

    4. Schlebusch H, Kern D. Stabilization of collagen by polyphenols. Angiologica 1972;9:248-56 [in German].

    5. Monboisse J, Braquet P, Randoux A, Borel J. Non-enzymatic degradation of acid-soluble calf skin collagen by superoxide ion: protective effect of flavonoids. Biochem Pharmacol 1983;32:53-8.

    6. Lagrue G, Olivier-Martin F, Grillot A. A study of the effects of procyanidol oligomers on capillary resistance in hypertension and in certain nephropathies. Sem Hop 1981;57:1399-401 [in French].

    7. Galley P, Thiollet M. A double-blind, placebo-controlled trial of a new veno-active flavonoid fraction (S 5682) in the treatment of symptomatic capillary fragility. Int Angiol 1993;12:69-72.

    8. Bruneton J. Pharmacognosy Phytochemistry Medicinal Plants. Andover: Intercept Ltd., 1995, 277.

    9. Robinson M, Lu B, Edirisinghe I, Kappagoda CT. Effect of grape seed extract on blood pressure in subjects with pre-hypertension. J Pharm Nutr Sci 2012;2:155-9.

    10. Ras RT, Zock PL, Zebregs YE, et al. Effect of polyphenol-rich grape seed extract on ambulatory blood pressure in subjects with pre- and stage I hypertension. Br J Nutr2013;110:2234-41.

    11. Fromantin M. Procyanidolic oligomers in the treatment of fragile capillaries and diabetic retinopathy. Med Int 1981;16:432-4 [in French].

    12. Verin MM, Vildy A, Maurin JF. Retinopathies and OPC. Bordeaux Medicale 1978;11:1467-74 [in French].

    13. Arne JL. Contribution to the study of procyanidolic oligomeres: Endotelon in diabetic retinopathy (in regard to 30 observations). Gaz Med de France 1982;89:3610-4 [in French].

    14. Cesarini JP, Michel L, Maurette JM, et al. Immediate effects of UV radiation on the skin: modification by an antioxidant complex containing carotenoids. Photodermatol Photoimmunol Photomed 2003;19:182-9.

    15. Greul AK, Grundmann JU, Heinrich F, et al. Photoprotection of UV-irradiated human skin: an antioxidative combination of vitamins E and C, carotenoids, selenium and proanthocyanidins. Skin Pharmacol Appl Skin Physiol 2002;15:307-15.

    16. La Ruche G, Cesarini JP. Protective effect of oral selenium plus copper associated with vitamin complex on sunburn cell formation in human skin. Photodermatol Photoimmunol Photomed 1991;8:232-5.

    17. Saliou C, Rimbach G, Moini H, et al. Solar ultraviolet-induced erythema in human skin and nuclear factor-kappa-B-dependent gene expression in keratinocytes are modulated by a French maritime pine bark extract. Free Radic Biol Med 2001;30:154-60.

    18. Banerjee B, Bagchi D. Beneficial effects of a novel IH636 grape seed proanthocyanidin extract in the treatment of chronic pancreatitis. Digestion 2001;63:203-6.

    19. Royer RJ, Schmidt CL. [Evaluation of venotropic drugs by venous gas plethysmography. A study of procyanidolic oligomers]. Sem Hop 1981;57:2009-13 [in French].

    This information does not replace the advice of a doctor. Healthwise, Incorporated, disclaims any warranty or liability for your use of this information. Your use of this information means that you agree to the Terms of Use. Learn how we develop our content.

    Healthwise, Healthwise for every health decision, and the Healthwise logo are trademarks of Healthwise, Incorporated.