OPC (Grape Seed Extract)

What the evidence says

OPC usually refers to oligomeric proanthocyanidin complexes, a family of polyphenols concentrated in grape seeds. Grape-seed extracts can differ substantially in proanthocyanidin content, polymer size, dose, and other constituents, so a milligram amount or an 'OPC' label does not guarantee equivalence to a product tested in a trial.^[1][2]

Blood-pressure evidence is inconsistent. A 2022 meta-analysis of 19 controlled trials found an average 2.2 mmHg reduction in diastolic pressure but no statistically significant effect on systolic pressure or flow-mediated dilation, with very high between-study heterogeneity. A small randomized trial in 30 adults with prehypertension reported lower systolic pressure at 400 mg per day, but endothelial function did not improve and the subgroup analyses were exploratory.^[2][3]

Lipid changes are similarly modest. A meta-analysis of 11 randomized trials found small average reductions in LDL cholesterol and triglycerides but no overall change in total or HDL cholesterol. A broader metabolic meta-analysis reported small reductions in fasting glucose, lipids, and C-reactive protein, but no improvement in HbA1c, HDL cholesterol, or body measurements. These surrogate changes do not prove prevention of heart attack, stroke, diabetes complications, or death.^[4][5]

Claims about generalized antioxidant protection, cancer prevention, cognition, skin rejuvenation, or longevity are not supported by adequate clinical evidence. NCCIH concludes that the best-studied areas are cholesterol and blood pressure, while even those conclusions are limited by small studies and variable products. Grape-seed extract should not replace proven treatment for hypertension or dyslipidemia.^[1][4][2]

Short studies generally describe oral grape-seed extract as well tolerated. Reported symptoms include mild nausea, headache, dizziness, or itching, often at rates similar to placebo. In one 29-person open-label safety study, two participants taking 2,500 mg per day developed temporary reductions in serum iron. Long-term safety is not established, pregnancy and breastfeeding data are sparse, and anyone taking medicines should review possible interactions with a clinician or pharmacist.^[7][6][1]