What kind of interaction is it?

Caution: an interaction that may reduce efficacy or raise side-effect risk and warrants monitoring.

Is this interaction backed by published research?

Yes. NutriStack lists 2 citation rows for the Grape Seed Extract + Warfarin pair, each linking to PubMed by PMID where available. Full sourcing methodology at https://nutristackapp.com/methodology/interactions.

Interaction databaseSupplement × PrescriptionReviewed May 2026

Grape Seed Extract and Warfarin, a caution.

Q: Can I take Grape Seed Extract and Warfarin together?

Possibly, but with caution. Grape Seed Extract and Warfarin have a documented caution-tier interaction. Grape seed extract contains procyanidins that inhibit platelet aggregation and prolong APTT and PT in vitro. A case report describes a stable warfarin patient developing a subcutaneous hematoma and INR of 7.9 within three days of starting grape seed extract drops. The mechanism is pharmacodynamic plus possible CYP inhibition.

Q: How does this affect a NutriStack Stack Score?

-5 to your Stack Score per scored caution row.

Grape seed extract contains procyanidins that inhibit platelet aggregation and prolong APTT and PT in vitro. A case report describes a stable warfarin patient developing a subcutaneous hematoma and INR of 7.9 within three days of starting grape seed extract drops. The mechanism is pharmacodynamic plus possible CYP inhibition.

2 primary source citations. Emerging evidence. Last verified May 30, 2026.

Open the interaction checker →Read the methodology

One pair, every claim cited. The two substances, the type, the mechanism, the recommendation, and the primary literature.
Same shape as the other 1,729 pairs in the public database.

Sourcing standards·Evidence tiers

From the interaction database

What the row says.

Every entry follows the same shape: what is happening, the mechanism, the recommendation, and the primary literature.

At a glance

Substances: Grape Seed Extract and Warfarin
Pair type: Caution
Evidence (highest tier): Emerging
Source citations: 2 sources
Stack Score effect: −5 to your Stack Score (per scored caution row).
Scope: Supplement × Prescription
Last verified: May 30, 2026

Caution · Emerging evidence

Caution

What is happening. Grape seed extract contains procyanidins that inhibit platelet aggregation and prolong APTT and PT in vitro. A case report describes a stable warfarin patient developing a subcutaneous hematoma and INR of 7.9 within three days of starting grape seed extract drops. The mechanism is pharmacodynamic plus possible CYP inhibition.

Mechanism. Procyanidins and oligomeric proanthocyanidins in grape seed extract inhibit collagen- and thrombin-induced platelet aggregation by binding platelet receptors and inhibiting protein tyrosine phosphatase signaling. They also prolong APTT, PT, and thrombin time, adding to warfarin's anticoagulation.

Recommendation. Avoid grape seed extract supplements while on warfarin. If unavoidable, keep the dose constant, watch for unusual bruising or bleeding, and ask your anticoagulation clinic for an INR check within 1-2 weeks of any change.

Sources (2)

Stack Score

How this pair moves the number.

Effect on the composite score

If both Grape Seed Extract and Warfarin are in the same stack, this pair applies −5 to your Stack Score (per scored caution row).

The full algorithm, the clamping rules, and four worked stacks are documented at /methodology/stack-score.

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