NutriStack
Evening Primrose Oil and Warfarin, a caution.
Evening primrose oil is rich in gamma-linolenic acid (GLA), which has documented antiplatelet activity and can prolong bleeding time. Adverse-event reviews of warfarin patients have flagged evening primrose oil as a supplement that may potentiate warfarin's effect.
One pair, every claim cited. The two substances, the type, the mechanism, the recommendation, and the primary literature.
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What the row says.
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At a glance
- Substances
- Evening Primrose Oil 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. Evening primrose oil is rich in gamma-linolenic acid (GLA), which has documented antiplatelet activity and can prolong bleeding time. Adverse-event reviews of warfarin patients have flagged evening primrose oil as a supplement that may potentiate warfarin's effect.
Mechanism. Gamma-linolenic acid is metabolised to dihomo-gamma-linolenic acid, which shifts platelet eicosanoid production toward less aggregatory prostaglandins (PGE1) and reduces thromboxane A2 production, lowering platelet aggregation.
Recommendation. Avoid evening primrose oil while on warfarin. If you take it for menstrual symptoms or skin conditions, tell your anticoagulation clinic, keep the dose constant, and ask for an INR check within 1-2 weeks.
Sources (2)
- Heck AM, DeWitt BA, Lukes AL. Potential interactions between alternative therapies and warfarin. Am J Health Syst Pharm. 2000;57(13):1221-7. PMID 10902065
- Tan CSS, Lee SWH. Warfarin and food, herbal or dietary supplement interactions: A systematic review. Br J Clin Pharmacol. 2021;87(2):352-374. PMID 32478963
Stack Score
How this pair moves the number.
Effect on the composite score
If both Evening Primrose Oil 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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