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Oligomeric Proanthocyanidins (OPCs)
What is it? Overview Usage Side Effects and Warnings

Oligomeric Proanthocyanidins (OPCs) Side Effects and Warnings

Written by FoundHealth.

Safety Issues

OPCs have been extensively tested for safety and are generally considered to be essentially nontoxic. 1 Side effects are rare, but when they do occur they are limited to occasional allergic reactions and mild digestive distress.

However, one study unexpectedly found that a combination of OPCs and vitamin C might slightly increase blood pressure in people with high blood pressure . 2 Neither treatment alone had this effect. These results may have been a statistical fluke, but nonetheless people with hypertension should use the combination of vitamin C and OPCs only with caution.

Maximum safe dosages for young children, pregnant or nursing women, or those with severe liver or kidney disease have not been established.

OPCs may have some anticoagulant properties when taken in high doses, and therefore should be used only under medical supervision by individuals on blood-thinner drugs, such as warfarin (Coumadin), heparin, clopidogrel (Plavix), ticlopidine (Ticlid), pentoxifylline (Trental), or aspirin.

Interactions You Should Know About

If you are taking:

  • Warfarin (Coumadin) , heparin , clopidogrel (Plavix), ticlopidine (Ticlid), pentoxifylline (Trental) , or aspirin : High doses of OPCs might cause a risk of excessive bleeding.


  1. Schulz V, Hansel R, Tyler VE. Rational Phytotherapy: A Physicians' Guide to Herbal Medicine. 3rd ed. Berlin, Germany: Springer Verlag; 1998:283.
  2. Ward NC, Hodgson JM, Croft KD, Burke V, Beilin LJ, Puddey IB. The combination of vitamin C and grape-seed polyphenols increases blood pressure: a randomized, double-blind, placebo-controlled trial. J Hypertens. 23(2):427-34.


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