Supplements and Warfarin sodium.
Warfarin sodium, sold under the brand names Coumadin, Jantoven, is a vitamin-K antagonist anticoagulant. It sits in a narrow therapeutic window monitored by INR.
Below are the 8 documented pairs we have explicitly assessed against Warfarin sodium in the Distil database: 2 red and 6 amber. The pairs cluster around 4 mechanisms: CYP induction, Vitamin K pathway, Additive anticoagulation, and Additive antiplatelet effect. Every call is cited to either a clinical reference (PMID) or the British National Formulary. Anything not on this list is either still to be assessed or beyond our database scope. The checker beneath surfaces assessments by supplement, and the missing-item form at the bottom of the page routes any uncatalogued supplement into our next curation pass.
Documented interactions
CYP induction
St John's Wort can cause your body to clear warfarin too quickly, dropping your INR and raising clot risk. Do not combine.
Vitamin K pathway
Vitamin K is the nutrient warfarin works against. Supplementing vitamin K can blunt warfarin's effect and raise clot risk. Do not start, stop, or change vitamin K supplements without your anticoagulation clinic's guidance.
CoQ10 has a similar molecular shape to vitamin K and may reduce warfarin's effect for some people. If you start or stop CoQ10 on warfarin, check INR within two weeks.
Additive anticoagulation
Curcumin may add to warfarin's blood-thinning effect. If you take warfarin, ask your GP before adding curcumin and monitor your INR closely if you do.
Quercetin may add to warfarin's blood-thinning effect at high doses. If you take warfarin, ask your GP before adding quercetin and monitor INR closely if you do.
Additive antiplatelet effect
Garlic at supplement doses has a mild blood-thinning effect of its own. Combined with warfarin, that can shift INR. If you take both, mention the garlic supplement to whoever monitors your INR and do not stop or start without telling them.
Ginkgo biloba has a mild antiplatelet effect of its own. The clinical data on whether it meaningfully shifts INR is mixed, but bleeding events have been reported, so combining with warfarin is best done with INR monitoring rather than freely.
At supplement doses below 1 gram per day, omega-3 fish oil has minimal effect on INR. At higher doses (3 grams per day and above) used for triglyceride lowering, the antiplatelet effect is more meaningful and INR can shift. Tell your GP what dose you take if you are on warfarin.
What this list does not say. Pairs not flagged here are not implicitly safe. They are either not yet in our database, or fall outside our inclusion scope (food-supplement interactions only; for drug-drug interactions, the BNF is authoritative). Use the checker below to surface any supplement, and submit a missing item if you take something we have not catalogued.
For adults over 18.
This tool gives evidence-graded information, not medical advice. Always discuss changes with your GP, pharmacist, or specialist before making them, especially if you take any medication, are pregnant, breastfeeding, or have a serious health condition.
How we grade severity, choose what's in scope, and what we exclude.
Every call on this page is reasoned. We publish the full rubric for severity tiers, the medication inclusion logic, the evidence grades we accept, and what we deliberately leave out. About three thousand words. Worth reading once if you use this tool more than occasionally.
Read the full methodologySomething missing?
If a supplement or medication you take isn't in our autocomplete, tell us and we'll add it in the next quarterly update.