Our approach
Plant polyphenol

Grape seed extract

CLimited evidence

At a glance

Typical studied dose
150–300 mg a dayOf standardised extract, usually for 4 to 16 weeks. Some trials went higher.
Average blood pressure fall
≈6 / 3 mmHgSystolic and diastolic, pooled across 16 trials and 810 people. An earlier 9-trial analysis found a much smaller systolic effect.
Who responded most
Under 50, BMI 25+The reduction was significant only in younger subjects and larger in those who were overweight or had metabolic disorders.
Effect on LDL cholesterol
Not significantPooled trials have not shown a reliable change in lipids.
Main interaction
Blood thinnersGrape seed polyphenols have anticoagulant and antiplatelet activity in laboratory studies.

What is Grape seed extract?

Grape seed extract is made from the seeds of grapes, usually Vitis vinifera, the species used for wine. The seeds are a by-product of wine and juice production, which is part of why the extract is cheap. What makes it interesting is its concentration of oligomeric proanthocyanidins, or OPCs: chains of polyphenol building blocks that also give red wine, tea and dark chocolate some of their bitterness and astringency. Good-quality extracts are standardised, typically to 90 per cent or more total polyphenols or to a stated OPC percentage. The number on the label only means something if that standardisation is given. "Grape seed 500 mg" with no percentage could be almost anything.

How it works

In laboratory work, grape seed polyphenols act as antioxidants, help the lining of blood vessels release nitric oxide, and reduce some markers of inflammation. The nitric oxide effect is the plausible link to blood pressure: blood vessels that relax more easily lower the pressure inside them. The word "antioxidant" deserves a caution, though. A compound that neutralises free radicals in a test tube does not necessarily do so in the body at the doses that are absorbed, and large trials of antioxidant supplements have repeatedly failed to show the benefits predicted from laboratory work. Proanthocyanidins are also poorly absorbed intact. Much of what reaches the bloodstream consists of smaller compounds made by gut bacteria, which may be responsible for part of the effect.

What the research actually shows

Evidence strength varies by what is being claimed, so each use is graded separately against the published criteria rather than averaged into one reassuring letter.

Lowering blood pressure

BModerate evidence

This is the claim the ingredient earns. A 2016 meta-analysis in Medicine pooled 16 randomised trials with 810 participants. It found average falls of about 6 mmHg systolic and 2.8 mmHg diastolic. That is similar in size to a meaningful cut in dietary salt, and smaller than a single blood pressure drug. The detail matters: the reduction was statistically significant only in trials of people under 50, and it was larger in people who were overweight or had metabolic disorders. An earlier 2011 meta-analysis of nine trials found a much smaller systolic effect, about 1.5 mmHg. B rather than A because the trials are small, they disagree about the size of the effect, and the benefit is concentrated in particular groups. It is a plausible add-on for someone with mildly raised blood pressure. It is not a replacement for prescribed treatment.

Sources: Zhang H et al, Feringa HHH et al

Improving cholesterol

DWeak evidence

The 2011 meta-analysis that looked at cardiovascular risk markers found no significant effect on LDL cholesterol, HDL cholesterol or triglycerides. Individual small trials have reported improvements, but they do not hold up when pooled. If cholesterol is the reason you are considering grape seed extract, the evidence points elsewhere, for example to soluble fibres such as psyllium, or to prescribed treatment where it is indicated.

Sources: Feringa HHH et al

Circulation and chronic venous insufficiency

DWeak evidence

Grape seed extract has a long history of use in parts of Europe for heavy, swollen legs and poor venous circulation, and there are older trials suggesting benefit. Most are small, short and methodologically weak by current standards. The idea is plausible given the effects on blood vessels, but it has not been tested properly.

General antioxidant protection and anti-ageing

DWeak evidence

Proanthocyanidins are powerful antioxidants in a test tube. That is true and nearly meaningless for a buyer. Antioxidant capacity measured in a laboratory does not predict health effects in people, and the large trials of antioxidant supplements, for vitamins E and C and beta-carotene, did not deliver the benefits the laboratory work promised. A label claiming "antioxidant protection" is describing chemistry, not an outcome anyone has shown in trials of grape seed extract.

Effective dosage

Blood pressure trials typically used 150 to 300 mg a day of standardised extract for 4 to 16 weeks, and a few used more. Look for a label that states the standardisation, commonly 90 to 95 per cent polyphenols or a stated OPC percentage. It is usually taken with food. If you are trying it for blood pressure, measure before you start and again after two to three months, on the same device at the same time of day. A home reading is the only way to know whether it is doing anything for you.

Where products diverge from the research. The gap here is usually standardisation rather than dose. A product listing "grape seed extract 100 mg" without a polyphenol or OPC percentage gives you no way to compare it with the trials, which used standardised extracts. Multi-ingredient "heart health" or "antioxidant" blends are worse: grape seed often appears as a small part of a proprietary blend at a fraction of the studied amount. The other trap is "grape extract" or "resveratrol", which are different materials from grape seed extract and should not borrow its evidence.

Safety, side effects and interactions

Grape seed extract is generally well tolerated in trials lasting up to several months. The reported side effects are mild: headache, nausea, stomach upset, dizziness and an itchy scalp. The one interaction worth taking seriously is with blood thinners. In laboratory studies grape seed polyphenols have anticoagulant and antiplatelet activity, so combining the extract with warfarin, clopidogrel, aspirin or similar drugs could in principle increase bleeding risk. Stop it before planned surgery, and check with a clinician if you take any of those drugs or have a bleeding disorder. Because it can lower blood pressure, anyone already on blood pressure medication should monitor their readings. There is not enough information on use in pregnancy or breastfeeding, and grape allergy is a contraindication.

None of this is medical advice. See the medical disclaimer for what that means before you act on anything here.

Common questions

Does grape seed extract lower blood pressure?

Modestly, in some people. A meta-analysis of 16 trials found average falls of about 6 mmHg systolic and 3 mmHg diastolic. The effect was clearest in people under 50 and in those who were overweight or had metabolic disorders. An earlier analysis found a smaller effect. If you try it, check your blood pressure before and after two to three months so you know whether it is working for you.

Can I take it instead of my blood pressure medication?

No. The average effect is smaller than a single blood pressure drug and inconsistent between people. If you take medication and want to add grape seed extract, talk to your clinician and keep monitoring, because the two effects could add together.

Does it lower cholesterol?

Not reliably. A 2011 meta-analysis of cardiovascular risk markers found no significant effect on LDL, HDL or triglycerides. Soluble fibres such as psyllium have much better evidence for LDL cholesterol.

What should I look for on the label?

A stated standardisation, such as "95% polyphenols" or a stated OPC percentage, and an amount of 150 to 300 mg a day. Without the standardisation there is no way to compare the product with the trials.

Is grape seed extract the same as resveratrol?

No. Resveratrol is a different polyphenol, found mainly in grape skins and in Japanese knotweed. Grape seed extract is rich in proanthocyanidins. They have different research bases, and one should not borrow the other’s evidence.

Is it safe with blood thinners?

Check with your doctor first. Grape seed polyphenols have anticoagulant and antiplatelet activity in laboratory studies, which could add to the effect of drugs such as warfarin, clopidogrel or aspirin. Stop taking it before planned surgery.

Related ingredients

Omega-3 (EPA and DHA) Green tea extract

Compiled by SNL Team