Grapes have been used medicinally for thousands of years. The ancient Greeks used grape leaves and sap for various ailments, though they had no scientific understanding of why these remedies might work. Modern interest in grape seed extract began in the 1970s when researchers started isolating and studying the compounds found in grape seeds.

What is grape seed extract?

Grape seed extract is a dietary supplement made from the seeds of wine grapes (Vitis vinifera). The seeds are dried, ground, and processed to concentrate specific compounds, particularly oligomeric proanthocyanidin complexes (OPCs).

Proanthocyanidins are a type of polyphenol found throughout the plant kingdom. They give certain foods their astringent taste and red, blue, or purple colouring. Besides grape seeds, you can find them in cranberries, pine bark (Pycnogenol), cocoa, blueberries, and red wine.

In laboratory studies, proanthocyanidins demonstrate antioxidant activity and can interact with cell signalling pathways. Whether these laboratory effects translate into meaningful health benefits when you swallow a capsule is a different question, and one that clinical trials have attempted to answer with mixed results.

How to take grape seed extract

Grape seed extract comes as capsules, tablets, or liquid extracts. Most supplements contain between 50 and 300 mg per dose.

There’s no established recommended dose because grape seed extract isn’t an approved medicine. Studies have used doses ranging from 100 to 600 mg daily, with most using around 150-300 mg. The duration of supplementation in clinical trials has varied from a few weeks to several months.

One thing to note: grape seed extract is not the same as grape seed oil (used for cooking) or resveratrol supplements. While resveratrol also comes from grapes, it’s a different compound with its own research profile.

What does the research actually show?

I’ve reviewed the clinical evidence for grape seed extract, and I should be honest from the start: the research base is smaller and less conclusive than the marketing might suggest. Most studies have been small, short-term, and the results have been inconsistent.

1. Blood pressure reduction

High blood pressure affects roughly 40% of adults over 25 worldwide, according to the World Health Organisation [1]. It’s a major risk factor for heart disease, stroke, and kidney failure, so anything that might help manage it gets attention.

A 2016 meta-analysis pooled data from 16 randomised controlled trials involving 810 participants [2]. The analysis found that grape seed extract did reduce blood pressure, but with some caveats. The effect was more pronounced in younger people, those who were obese, and patients with metabolic conditions. In healthy people with normal blood pressure, the effect was minimal.

The proposed mechanism involves polyphenols enhancing nitric oxide activity, which relaxes blood vessels. This is plausible, but the meta-analysis authors noted significant heterogeneity between studies. Some showed clear benefits; others showed almost nothing.

My take: if you already have high blood pressure (which can also cause urinary symptoms), grape seed extract isn’t going to replace medication. But it might provide modest additional support alongside proper medical treatment.

2. Non-alcoholic fatty liver disease

Non-alcoholic fatty liver disease (NAFLD) is increasingly common, largely driven by rising obesity rates. It ranges from simple fat accumulation to more serious inflammation (steatohepatitis) that can progress to cirrhosis.

A 2010 randomised controlled trial studied 30 patients with NAFLD over three months [3]. Half received grape seed extract; half received vitamin C as a control. The grape seed group showed improved liver enzyme levels (AST) and reduced fat accumulation on ultrasound compared to the vitamin C group.

This is interesting but far from conclusive. Thirty patients over three months is a small trial. We don’t know if the benefits persist long-term, or if the ultrasound improvements translate into meaningful clinical outcomes. Still, for people looking at supplements that might support liver health, this provides some early evidence worth watching.

3. Chronic kidney disease

Chronic kidney disease is defined as reduced kidney function (glomerular filtration rate below 60 mL/min/1.73m²) persisting for at least three months. It’s a progressive condition that can eventually require dialysis. The main risk factors include diabetes, high blood pressure, and age.

A 2016 randomised, double-blind, placebo-controlled trial followed 33 patients with chronic kidney disease for six months [4]. Those taking grape seed extract showed improvements in glomerular filtration rate, proteinuria (protein in urine), inflammatory markers (CRP), and triglyceride levels.

Thirty-three patients isn’t a large trial, but the results were statistically significant across multiple markers. The findings suggest grape seed extract might slow disease progression or reduce associated cardiovascular risk. However, I wouldn’t take this to mean grape seed extract treats kidney problems or kidney stones. Far more research is needed before making that claim.

4. Menopause symptoms

About 85% of women experience at least one menopausal symptom, whether that’s hot flushes, night sweats, sleep disturbances, or mood changes.

An 8-week randomised, double-blind, placebo-controlled trial enrolled 96 women aged 40-60 with menopausal symptoms [5]. The grape seed extract group reported improvements in hot flushes, anxiety, and insomnia. They also showed increased muscle mass and reduced blood pressure (about 5 mmHg on average).

The results are promising, though the trial was short. Many women have menopausal symptoms for years, so we’d need longer studies to know if benefits persist. There’s also the question of how grape seed extract compares to other options like soy isoflavones, which have a longer research history for menopausal symptoms.

5. Reducing chemotherapy side effects

This is perhaps the most intriguing area of grape seed research, though it remains largely preclinical.

A 2015 systematic review examined 41 in vitro (lab dish) and animal studies [6]. The findings suggested grape seed proanthocyanidins might protect normal cells from damage during chemotherapy or radiation therapy, while not interfering with the treatment’s effectiveness against cancer cells.

The drugs studied included doxorubicin, cisplatin, methotrexate, 5-fluorouracil, and cyclophosphamide, which are common chemotherapy agents known for causing significant side effects like nausea, fatigue, and mouth ulcers.

I should be clear: this research is pre-clinical. Laboratory and animal findings don’t always translate to humans. Nobody should start taking grape seed extract during cancer treatment without discussing it with their oncologist. Some supplements can interfere with chemotherapy drugs in unpredictable ways. But as an area for future research, the preliminary findings are worth noting.

Side effects

Grape seed extract appears to be reasonably well tolerated in most people. Side effects reported in clinical trials include:

Headache
Sore throat
Stomach pain
Nausea
Dizziness
Itchy scalp

These side effects were generally mild and similar in frequency to placebo groups in controlled trials. The NHS notes that grape seed extract is generally considered safe for short-term use [7].

Safety precautions and contraindications

1. Grape allergy

If you’ve had allergic reactions to grapes, grape products, or wine, avoid grape seed extract. Allergic reactions can include facial or hand swelling, throat tightness, difficulty breathing, and hives. If you experience any of these symptoms, stop taking the supplement and seek medical attention.

2. Pregnancy and breastfeeding

There’s insufficient safety data for grape seed extract during pregnancy or breastfeeding. Most clinical trials have excluded pregnant and nursing women. Until more data is available, it’s sensible to avoid grape seed extract during these periods.

3. Blood-thinning effects

Grape seed extract may have anticoagulant properties. If you’re taking blood-thinning medications like warfarin, clopidogrel, or aspirin, discuss grape seed extract with your doctor before starting. The combination could theoretically increase bleeding risk.

Similarly, if you have a bleeding disorder or are scheduled for surgery, stop grape seed extract at least two weeks beforehand to reduce bleeding risk during the procedure.

4. Drug interactions and existing conditions

If you have liver or kidney disease, talk to your doctor before supplementing. While some research suggests potential benefits, the safety profile in people with existing organ impairment isn’t fully established.

Grape seed extract may interact with various medications beyond blood thinners, including some processed by liver enzymes. If you’re taking multiple medications, check with your pharmacist or doctor about potential interactions.

The bottom line

Grape seed extract is a dietary supplement with some interesting preliminary research behind it. The evidence for modest blood pressure reduction in certain populations is probably the strongest, though even that comes with caveats about study quality and heterogeneity.

For other conditions, the research is earlier stage. Small trials with promising results need replication in larger studies before we can make confident recommendations.

If you’re considering grape seed extract, it’s not a replacement for medical treatment, a healthy diet, or lifestyle modifications. At best, it might provide marginal additional support. At worst, it’s an expensive way to produce slightly more colourful urine.

Talk to your doctor if you’re interested in trying it, particularly if you have existing health conditions or take medications.

References

World Health Organization. Hypertension. https://www.who.int/news-room/fact-sheets/detail/hypertension
Zhang H, Liu S, Li L, et al. The impact of grape seed extract treatment on blood pressure changes: A meta-analysis of 16 randomized controlled trials. Medicine (Baltimore). 2016;95(33):e4247. https://pubmed.ncbi.nlm.nih.gov/27537554/
Khoshbaten M, Aliasgarzadeh A, Masnadi K, et al. Grape seed extract to improve liver function in patients with nonalcoholic fatty liver change. Saudi J Gastroenterol. 2010;16(3):194-197. https://pubmed.ncbi.nlm.nih.gov/20616415/
Turki K, Charradi K, Boukhalfa H, et al. Grape seed powder improves renal failure of chronic kidney disease patients. EXCLI J. 2016;15:424-433. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5083963/
Terauchi M, Horiguchi N, Kajiyama A, et al. Effects of grape seed proanthocyanidin extract on menopausal symptoms, body composition, and cardiovascular parameters in middle-aged women: a randomized, double-blind, placebo-controlled pilot study. Menopause. 2014;21(9):990-996. https://pubmed.ncbi.nlm.nih.gov/24518152/
Vaid M, Singh T, Prasad R, et al. Grape seed proanthocyanidins for protection from environmental toxicants. Mol Nutr Food Res. 2015;59(6):1078-1093. https://pubmed.ncbi.nlm.nih.gov/25880972/
NHS. Vitamins and minerals - Others. https://www.nhs.uk/conditions/vitamins-and-minerals/others/