Grape Seed Extract and Pine Bark Extract: Oligomeric Proanthocyanidins and Evidence
What grape seed and pine bark extracts contain, what reviews found for blood pressure, leg veins and chronic conditions, and the bleeding and medicine cautions to know about.
Content last updated . This page has not been medically reviewed.
What is Grape seed extract and pine bark extract (oligomeric proanthocyanidins, OPC) good for?
What the body uses it for, and how strong the evidence is. A normal job in the body is not proof that extra supplements add benefit; each card says which.
Plant antioxidant compounds (lab activity)
Lab or animal research onlyGrape seed and pine bark extracts contain procyanidins and related compounds that act as antioxidants in laboratory tests. This shows chemistry, not a proven health benefit from taking them.
Supplements: Raising a blood antioxidant marker is not a health outcome; no good evidence that this prevents disease or slows ageing.
Blood pressure (grape seed extract)
Preliminary or mixedTwo reviews of grape seed extract trials found small drops in blood pressure, but they disagreed on systolic pressure and the trials varied widely. Pine bark reviews found no blood pressure benefit.
Supplements: Small and inconsistent changes in small trials; not a replacement for blood pressure treatment.
Leg vein problems (chronic venous insufficiency)
Not enough evidenceGrape seed and pine bark were each only a small part of a large review of oral vein-support products, which found a slight reduction in leg swelling for the group overall. Findings for these two extracts specifically are too limited to judge.
Supplements: Insufficient evidence for these specific extracts; the group of vein-support products made little difference to quality of life.
Chronic conditions (pine bark extract)
Not enough evidenceA Cochrane review of 15 small trials of a pine bark extract in seven conditions, including asthma, diabetes, high blood pressure and osteoarthritis, found the evidence insufficient to support its use for any chronic disorder.
Supplements: Insufficient evidence; trials were small and varied.
Cholesterol and blood markers (grape seed)
Preliminary or mixedPreliminary human studies suggest grape seed extract may lower LDL cholesterol, but results for fats, glucose and inflammation markers are mixed.
Supplements: Mixed marker results; not shown to prevent heart disease.
Diabetic eye disease (grape seed, adjunct)
Preliminary or mixedOne source notes a possible extra benefit of grape seed extract alongside usual care in diabetic retinopathy. This is preliminary.
Supplements: Preliminary only; do not use in place of eye care or diabetes treatment.
Joint, menopause and pain symptoms (pine bark)
Preliminary or mixedSmall early human studies of pine bark extract suggest possible effects on osteoarthritis symptoms, menopausal symptoms and period pain. The evidence is limited.
Supplements: Evidence is limited and from small studies.
Radiotherapy skin effects (grape seed)
Not enough evidenceOral grape seed extract did not improve tissue hardness, pain or tenderness in breast cancer patients after radiotherapy.
Supplements: No good evidence of benefit in the study reported.
Connected topics
Open a group to see how each topic connects and how strong the evidence is.
Health goals (3)
- Blood Pressure SupportPreliminary or mixed
Two grape seed meta-analyses found small drops, but they differed on systolic pressure and trials varied widely; pine bark reviews found no benefit.
- Cellular ProtectionLab or animal research only
Antioxidant activity in the lab; this is not proof that supplements protect cells in people.
- Heart HealthPreliminary or mixed
Small, inconsistent changes in blood pressure and heart rate in grape seed trials; no proof of fewer heart events.
Body systems (2)
- Cardiovascular SystemPreliminary or mixed
Grape seed extract trials show small, inconsistent effects on blood pressure and heart rate; confirmation in larger trials is needed.
- Heart & CirculationPreliminary or mixed
Grape seed extract trials show small, inconsistent effects on blood pressure and heart rate; no proof of fewer heart problems.
Body parts (1)
- Blood VesselsPreliminary or mixed
Studied for blood pressure and vessel widening (flow-mediated dilation); the 2022 review found no significant change in vessel widening.
Functional actions (2)
- AntioxidantLab or animal research only
The compounds act as antioxidants in the lab and raised a blood antioxidant marker in preliminary studies; that does not prove a health benefit from supplements.
- Cardiovascular SupportPreliminary or mixed
Grape seed trials show small, inconsistent changes in blood pressure and heart rate; pine bark reviews found no blood pressure benefit.
Root causes (2)
- Medication Side EffectsDocumented risk
May increase bleeding risk with warfarin-type blood thinners, and grape seed extract affected liver drug-processing enzymes in the lab. Ask a pharmacist about your medicines.
- Oxidative StressLab or animal research only
The extracts counter oxidative stress in lab studies. Whether supplements change disease risk linked to oxidative stress is not shown.
Documented risks and interactions (2)
- Bleeding risk with blood thinners. Grape seed extract showed antiplatelet activity in the lab, and pine bark may raise bleeding risk with warfarin-type drugs. People on blood thinners should ask their prescriber or pharmacist first.
- Interaction with medicines processed by liver enzymes. In laboratory tests grape seed extract inhibited the liver enzyme CYP3A4 and affected UGT enzymes, which could change how some medicines behave. Whether this matters in people is not established.
What these products are
Grape seed extract is made from the seeds of wine grapes and sold as tablets, capsules and liquid extracts. [1] Its main compounds are proanthocyanidins, which also occur naturally in fruits, vegetables, chocolate and tea. [1] Memorial Sloan Kettering Cancer Center notes that people generally consume 460 to 1,000 mg a day of these combined substances (population and country not stated). [1]Pine bark extract here means extracts from the bark of French maritime pine. A Cochrane review describes the one it assessed as standardized to contain 70 percent procyanidin. [2] "OPC" (oligomeric proanthocyanidins) is a label used for such products. The sources we read do not define a standard amount or composition for it, so two products can differ.
Do not confuse grape seed extract with grapefruit seed extract, which has different biological effects. [1] For the compound class, see polyphenols and their main classes.
What reviews found
Evidence labels: mixed, insufficient evidence and promising but limited. Findings for one extract do not transfer to the other. Blood markers, such as total antioxidant activity, are not health outcomes. Sloan Kettering lists increased serum antioxidant activity among preliminary human findings for grape seed extract. [1]| Extract and question | What the source found | Label |
|---|---|---|
| Grape seed, blood pressure | A 2016 meta-analysis of 16 trials (810 people) found systolic pressure fell by about 6.1 mmHg and diastolic by about 2.8 mmHg, with larger drops in younger, obese or metabolic-syndrome groups, and called for larger trials. [3] A 2022 meta-analysis of 19 trials found diastolic pressure fell 2.2 mmHg and heart rate 1.25 beats per minute, but no significant change in systolic pressure or in flow-mediated dilation (how widely arteries open); results varied widely between trials. [4] | Mixed |
| Grape seed, leg vein problems | One grape seed trial was among 69 trials in a Cochrane review of oral vein-support products, which overall probably reduced leg swelling slightly and made little difference to quality of life. Findings for specific products were limited. [5] | Insufficient evidence |
| Grape seed, radiotherapy skin effects | Oral grape seed extract did not improve tissue hardness, pain or tenderness in breast cancer patients after radiotherapy. [1] | No good evidence of benefit |
| Pine bark, chronic conditions | A 2012 Cochrane review of 15 trials (791 people) across seven conditions, including asthma, diabetes, high blood pressure and osteoarthritis, found evidence insufficient to support use for any chronic disorder; the trials were small and varied. [2] | Insufficient evidence |
Proper evidence not found for a newer systematic review of pine bark extract that we could read this round; the Cochrane review dates from 2012. We searched PubMed for pine bark and chronic venous insufficiency and for pine bark systematic reviews.
Frequently asked questions
Does grape seed extract lower blood pressure?
Two meta-analyses found small drops, but they differed on systolic pressure and trials varied widely. [3][4]
Does pine bark extract treat any condition?
A 2012 Cochrane review found insufficient evidence for any chronic disorder. [2]
What does OPC mean on a label?
It stands for oligomeric proanthocyanidins, a plant compound group. The sources we read give no standard amount, so compare ingredient forms carefully.
Can I take it with a blood thinner?
Sloan Kettering says grape seed extract may increase bleeding risk with warfarin and similar drugs. [1] Ask your prescriber or pharmacist.
Is grape seed extract the same as grapefruit seed extract?
No. They have different biological effects. [1]
More details: evidence, limits and cautions
The details behind this page: cautions, limits of the evidence and where sources disagree. Open any note to read it.
Safety
- Reported effects. Sloan Kettering's patient page says side effects have not been reported for grape seed extract, while its clinician section lists gastrointestinal upset. [1]
- Bleeding. In the lab, grape seed has antiplatelet activity, and Sloan Kettering tells people on blood thinners such as warfarin to talk with their provider because bleeding risk may rise. [1] Clinical relevance is not yet determined. [1]
- Other medicines. In the lab, grape seed extract inhibited CYP3A4 and modulated UGT enzymes, which may affect drugs processed that way. [1] Pharmacists can check your list; see medication interactions.
- Vein-support products in general. Cochrane found they probably increase side effects slightly, mostly gastrointestinal, and only short-term safety was studied. [5]
- Pine bark and children. Two of the 15 pine bark trials were in children only, but the review said no definitive safety conclusion was possible. [2]
Pregnancy, breastfeeding, kidney or liver disease and surgery. Not described in the sources we read for either extract. Lack of evidence is not proof of safety. See pregnancy and breastfeeding, supplements before surgery and quality testing and certifications. Talk to a clinician or pharmacist before use, particularly if you take a blood thinner.
References
- Grape Seed. Memorial Sloan Kettering Cancer Center, About Herbs (US). Read 2026-10-23.
- Cochrane review of French maritime pine bark extract for chronic disorders (2012). The Cochrane database of systematic reviews (2012). PubMed abstract. Abstract read on PubMed. Product trade name omitted. Read 2026-10-23.
- The impact of grape seed extract treatment on blood pressure changes: A meta-analysis of 16 randomized controlled trials. Medicine (2016). PubMed abstract. Read 2026-10-23.
- The effect of grape (Vitis vinifera) seed extract supplementation on flow-mediated dilation, blood pressure, and heart rate: A systematic review and meta-analysis of controlled trials with duration- and dose-response analysis. Pharmacological research (2022). PubMed abstract. Read 2026-10-23.
- Phlebotonics for venous insufficiency. The Cochrane database of systematic reviews (2020). PubMed abstract. Read 2026-10-23.