NutriStack
Garlic Extract and Warfarin, a caution.
Garlic supplements possess antiplatelet properties that may increase bleeding risk when combined with warfarin. Several case reports have documented elevated INR and bleeding episodes in patients taking garlic supplements with warfarin. The effect is more pronounced with concentrated garlic extracts than with culinary amounts.
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
- Garlic Extract and Warfarin
- Pair type
- Caution
- Evidence (highest tier)
- Moderate
- Source citations
- 6 sources
- Stack Score effect
- −5 to your Stack Score (per scored caution row).
- Scope
- Supplement × Prescription
- Last verified
- May 30, 2026
Caution · Moderate evidence
Caution
What is happening. Garlic supplements possess antiplatelet properties that may increase bleeding risk when combined with warfarin. Several case reports have documented elevated INR and bleeding episodes in patients taking garlic supplements with warfarin. The effect is more pronounced with concentrated garlic extracts than with culinary amounts.
Mechanism. Allicin and ajoene in garlic inhibit platelet aggregation via multiple mechanisms including thromboxane synthesis inhibition, phospholipase activity modulation, and calcium mobilization interference in platelets.
Recommendation. Avoid concentrated garlic supplements while on warfarin. Moderate culinary use of garlic is generally safe. If you use garlic supplements, inform your prescriber and monitor INR more frequently.
Sources (6)
- Macan H et al. Aged garlic extract may be safe for patients on warfarin therapy. J Nutr. 2006;136(3 Suppl):793S-795S. PMID 16484565
- Scharbert G et al. Garlic at dietary doses does not impair platelet function. Anesth Analg. 2007;105(5):1214-1218. PMID 17959944
- Wang M, Zeraatkar D, Obeda M, Lee M et al.. Drug-drug interactions with warfarin: A systematic review and meta-analysis. British Journal of Clinical Pharmacology. 2021. PMID 33769581
- Saadh MJ, Kariem M, Shukla M et al.. Effects of aged garlic extract on blood pressure in hypertensive patients: A systematic review and meta-analysis of randomized controlled trials. Prostaglandins & Other Lipid Mediators. 2024. PMID 39437887
- Gadidala SK, Johny E, Thomas C et al.. Effect of garlic extract on markers of lipid metabolism and inflammation in coronary artery disease (CAD) patients: A systematic review and meta-analysis. Phytotherapy Research. 2023. PMID 36640154
- Mirzavandi F, Mollahosseini M, Salehi-Abargouei A et al.. Effects of garlic supplementation on serum inflammatory markers: A systematic review and meta-analysis of randomized controlled trials. Diabetes & Metabolic Syndrome. 2020. PMID 32673835
Stack Score
How this pair moves the number.
Effect on the composite score
If both Garlic 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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