Supplements and Warfarin sodium.
Warfarin sodium, sold under the brand names Coumadin, Jantoven, Marevan, is a vitamin-K antagonist anticoagulant. It sits in a narrow therapeutic window monitored by INR.
Warfarin is the original vitamin K antagonist, largely displaced by DOACs but still prescribed for mechanical heart valves and antiphospholipid syndrome. The narrow therapeutic window is why INR is measured regularly: too little leaves stroke risk, too much drives bleeding. Vitamin K opposes warfarin directly, in supplements and in K2-rich foods like natto, though nattokinase supplements may add bleeding risk. Curcumin's caution rests on antiplatelet activity and one reported case of a sharply raised INR; a human study found no CYP2C9 effect. Garlic and ginkgo come up most often, but the mechanism is additive antiplatelet effect rather than a change in warfarin levels: randomised crossover trials found neither altered warfarin pharmacokinetics or INR (Jiang 2005, Mohammed Abdul 2008). The bleeding case reports are real, and an antiplatelet effect can raise bleeding risk while INR sits unchanged, so both belong with the anticoagulant clinic rather than in an INR reading. St John's Wort induces CYP and drops INR, raising clot risk, and that combination is hard excluded. Cranberry acts on warfarin's own pathway rather than on CYP2C9. Cases cluster at high juice volumes, but capsules equivalent to 57g of fruit daily raised the INR response, so extracts need monitoring too.
Below are the 28 documented pairs we have explicitly assessed against Warfarin sodium in the Distil database: 2 severe and 26 caution. The pairs cluster around 8 mechanisms: CYP induction, Vitamin K pathway, Additive anticoagulation, Reduced anticoagulant effect, Additive antiplatelet effect, CYP-mediated metabolism, CYP2C9 inhibition, and Nrf2 + CYP modulation. 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
Last reviewed 12 November 2026. Each interaction below lists the evidence its assessment drew on: some rest on studies of the exact pair, others on mechanism evidence, where a citation may support one part of the reasoning rather than the exact combination. The evidence line on each entry says which.
CYP induction
Severe Does St John's Wort interact with Warfarin sodium?
St John's Wort can cause your body to clear warfarin too quickly, dropping your INR and raising clot risk. Do not combine.
Evidence: Supported by human study data.
Caution Does Panax Ginseng interact with Warfarin sodium?
Ginseng tends to work against warfarin rather than with it. Some people on warfarin see their INR drop when they add ginseng, which can leave them under-protected against clots. The evidence is mixed between ginseng types, so if you take warfarin, tell your anticoagulation clinic before starting ginseng and ask for an INR check a couple of weeks in.
Evidence: Supported by human study data.
Reviewer-flagged: awaiting clinical-reviewer sign-off.
Vitamin K pathway
Severe Does Vitamin K2 interact with Warfarin sodium?
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.
Evidence: Supported by human study data.
Caution Does Coenzyme Q10 interact with Warfarin sodium?
CoQ10 is structurally related to vitamin K, and case reports describe it reducing warfarin's effect, though a small trial in people on long-term warfarin found no change at 100 mg a day. If you start or stop CoQ10 on warfarin, check INR within two weeks.
Evidence: Limited human data, from small studies or case reports.
Reviewer-flagged: awaiting clinical-reviewer sign-off.
Additive anticoagulation
Caution Does Andrographis interact with Warfarin sodium?
Andrographis may raise warfarin's effect, both by mild blood-thinning of its own and by slowing how the body clears warfarin. The direct warfarin evidence so far is from animal studies rather than people. If you take warfarin, tell your anticoagulation clinic before starting andrographis and ask for an INR check a couple of weeks in.
Evidence: No direct study of this exact combination yet; the caution rests on a plausible mechanism or on reports involving a related medicine.
Reviewer-flagged: awaiting clinical-reviewer sign-off.
Caution Does Bromelain interact with Warfarin sodium?
Bromelain has a mild blood-thinning effect of its own and may add to warfarin's. If you take warfarin, tell whoever monitors your INR before adding bromelain and check your INR if you do start it. If you have surgery planned, mention bromelain to your team; stopping high-dose bromelain about two weeks beforehand is a common precaution.
Evidence: Limited human data, from small studies or case reports.
Reviewer-flagged: awaiting clinical-reviewer sign-off.
Caution Does Cinnamon interact with Warfarin sodium?
Whether cinnamon adds to warfarin's effect depends on the type: Cassia cinnamon, the common supermarket kind, contains coumarin, a natural compound that can act like a mild blood thinner at high regular intake, while Ceylon (true) cinnamon contains far less. Do not read that as a guarantee: the one reported human case of a cinnamon-related bleeding problem involved Ceylon cinnamon taken at about a tablespoon a day for ten months. A pinch on food is not the issue; the concern is large daily doses or concentrated cinnamon supplements of either type. If you take warfarin and use cinnamon regularly in large amounts, tell your GP and check your INR.
Evidence: Limited human data, from small studies or case reports.
Reviewer-flagged: awaiting clinical-reviewer sign-off.
Caution Does Cordyceps interact with Warfarin sodium?
Cordyceps may add to warfarin's blood-thinning effect through a mild antiplatelet action of its own. This is based on laboratory work on human platelets rather than studies in people taking warfarin, so the real-world size of the effect is unknown. If you take warfarin, mention cordyceps to your anticoagulation clinic and ask whether an INR check is worth doing after you start.
Evidence: No direct study of this exact combination yet; the caution rests on a plausible mechanism or on reports involving a related medicine.
Reviewer-flagged: awaiting clinical-reviewer sign-off.
Caution Does Cranberry Extract (PAC-standardised) interact with Warfarin sodium?
Cranberry can push warfarin's blood-thinning effect higher. Most case reports involve large volumes of juice, but in a controlled trial cranberry capsules raised warfarin's effect too, so tell your GP whichever form you take and ask whether INR monitoring should be a little tighter for the first few weeks.
Evidence: Supported by human study data.
Reviewer-flagged: awaiting clinical-reviewer sign-off.
Caution Does Curcumin interact with Warfarin sodium?
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.
Evidence: Limited human data, from small studies or case reports.
Reviewer-flagged: awaiting clinical-reviewer sign-off.
Caution Does Fisetin interact with Warfarin sodium?
Fisetin may mildly thin the blood by reducing how platelets clump, which could add to warfarin and nudge bleeding risk up. The concern is with a high-dose fisetin course, not the small amount in food. If you take warfarin, tell your anticoagulant clinic before starting a fisetin course and expect closer INR checks at first.
Evidence: No direct study of this exact combination yet; the caution rests on a plausible mechanism or on reports involving a related medicine.
Reviewer-flagged: awaiting clinical-reviewer sign-off.
Caution Does Ginger interact with Warfarin sodium?
Ginger has a reputation for thinning the blood, but the controlled studies are reassuring. When ginger was given to people taking warfarin in proper trials, it did not change their INR or how warfarin behaved. A small number of case reports describe raised INR or bleeding, so the safe approach is to keep your ginger intake steady rather than suddenly taking large supplement doses, and to mention it to whoever monitors your INR. There is no need to avoid normal dietary ginger.
Evidence: Limited human data, from small studies or case reports.
Reviewer-flagged: awaiting clinical-reviewer sign-off.
Caution Does Glucosamine interact with Warfarin sodium?
Glucosamine can push warfarin's blood-thinning effect higher, raising your INR and your bleeding risk. This shows up more when the glucosamine dose goes up. If you take warfarin, tell your anticoagulation clinic before starting glucosamine and ask for an INR check within a couple of weeks, especially if you change the dose.
Evidence: Supported by human study data.
Caution Does L-Carnitine interact with Warfarin sodium?
Two published case reports describe L-carnitine making acenocoumarol, a close relative of warfarin, work more strongly, and in the more recent one the INR settled once L-carnitine was stopped. Neither involved warfarin itself, so the evidence for warfarin is thin. If you take warfarin, mention L-carnitine to your anticoagulation clinic and ask whether an INR check is worth doing after you start.
Evidence: No direct study of this exact combination yet; the caution rests on a plausible mechanism or on reports involving a related medicine.
Reviewer-flagged: awaiting clinical-reviewer sign-off.
Caution Does Pine Bark Extract interact with Warfarin sodium?
Pine bark extract (pycnogenol) has a mild blood-thinning effect of its own, shown in people as reduced platelet stickiness, but only in smokers: in the same study it made no measurable difference to non-smokers. It has not been studied alongside warfarin, so the size of any combined effect is unknown. If you take warfarin, tell your anticoagulation clinic before starting pine bark extract and ask for an INR check a couple of weeks in.
Evidence: No direct study of this exact combination yet; the caution rests on a plausible mechanism or on reports involving a related medicine.
Reviewer-flagged: awaiting clinical-reviewer sign-off.
Caution Does Quercetin interact with Warfarin sodium?
Quercetin may, in theory, add to warfarin's blood-thinning effect at high doses, though a small human study found no change in INR. If you take warfarin, mention any high-dose quercetin to your GP and monitor your INR if you start it.
Evidence: Limited human data, from small studies or case reports.
Caution Does Resveratrol interact with Warfarin sodium?
Resveratrol can act on warfarin in two ways: it can slow how the body clears warfarin and it can mildly thin the blood by reducing how platelets clump. Both could nudge your INR up and raise bleeding risk. The concern is with supplement doses, not the small amount in food. If you take warfarin, tell your anticoagulant clinic before starting resveratrol and expect closer INR checks at first.
Evidence: No direct study of this exact combination yet; the caution rests on a plausible mechanism or on reports involving a related medicine.
Reviewer-flagged: awaiting clinical-reviewer sign-off.
Caution Does Spirulina interact with Warfarin sodium?
Spirulina has a mild antiplatelet signal in laboratory studies, but a human trial at a high dose found no change in clotting tests or platelet activity. Any effect on warfarin is likely to be small. If you take warfarin, keep your spirulina intake steady rather than starting or stopping suddenly, and tell your anticoagulation clinic what you take.
Evidence: No direct study of this exact combination yet; the caution rests on a plausible mechanism or on reports involving a related medicine.
Reviewer-flagged: awaiting clinical-reviewer sign-off.
Reduced anticoagulant effect
Caution Does Collagen Precursors interact with Warfarin sodium?
The 1,000 mg of vitamin C in this collagen precursor blend (a high daily dose) may make warfarin work less well, so your INR (the blood test that shows how thinned your blood is) drops below the level you need. There are reports of vitamin C supplements doing this, one at 200 mg twice a day, with the INR coming back up once the vitamin C was stopped. If you take warfarin, tell whoever manages it before starting or stopping this blend, so your INR can be watched and kept stable.
Evidence: Limited human data, from small studies or case reports.
Reviewer-flagged: awaiting clinical-reviewer sign-off.
Caution Does Green Tea Extract interact with Warfarin sodium?
Very large amounts of green tea have been reported to work against warfarin: one man's INR fell after he began drinking two to four litres a day, and recovered when he stopped. Why is not settled, since brewed tea carries very little vitamin K. Whether a concentrated extract capsule does the same is unknown, so it is not safe to assume a capsule is exempt. Either way, keep your green tea habit steady rather than changing it suddenly while on warfarin, and tell your anticoagulation clinic what you take.
Evidence: Limited human data, from small studies or case reports.
Reviewer-flagged: awaiting clinical-reviewer sign-off.
Caution Does Vitamin C interact with Warfarin sodium?
There are rare reports of vitamin C supplements making warfarin work less well, so your INR (the blood test that shows how thinned your blood is) drops below the level you need. In the two recent case reports the INR came back up once the vitamin C was stopped. One of those people was taking 200 mg twice a day, an ordinary supplement dose, so a low-dose supplement cannot be assumed to be exempt. Vitamin C from food is not the concern. If you take a vitamin C supplement alongside warfarin, tell whoever manages your warfarin so your INR can be watched, keep the dose steady, and let them know before you start or stop it.
Evidence: Limited human data, from small studies or case reports.
Reviewer-flagged: awaiting clinical-reviewer sign-off.
Additive antiplatelet effect
Caution Does Garlic Extract interact with Warfarin sodium?
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.
Evidence: Supported by human study data.
Caution Does Ginkgo Biloba interact with Warfarin sodium?
Ginkgo has been linked to reports of bleeding, and bleeding with ginkgo and warfarin together is among the herb and medicine interactions reported most often in older adults. In trials in people, ginkgo at the 120 to 240mg doses sold in the UK has not shown a meaningful effect on standard clotting tests, and two small controlled studies found no change in INR, so the caution rests on the bleeding reports: take the two together only with INR monitoring agreed with your anticoagulant clinic.
Evidence: Supported by human study data.
Caution Does Omega-3 EPA interact with Warfarin sodium?
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.
Evidence: Limited human data, from small studies or case reports.
Caution Does Vitamin E interact with Warfarin sodium?
A small double-blind trial in people on long-term warfarin found vitamin E did not change their INR, but it did not count bleeding events, and vitamin E has a mild blood-thinning effect of its own that an INR reading would not show, so a low dose cannot be assumed to add nothing. Tell your anticoagulant clinic before taking vitamin E at any dose, and stop it at least two weeks before planned surgery.
Evidence: Limited human data, from small studies or case reports.
CYP-mediated metabolism
Caution Does Schisandra interact with Warfarin sodium?
Schisandra may change how quickly your body clears warfarin, which could move your INR. In a study in rats, a schisandra extract made the body clear warfarin faster, which in people would weaken warfarin's effect, but this has not been tested in people, and other studies point to schisandra slowing some drug-clearing enzymes instead. Tell whoever manages your warfarin before you start schisandra, keep to your usual INR checks, and do not change your warfarin dose yourself.
Evidence: No direct study of this exact combination yet; the caution rests on a plausible mechanism or on reports involving a related medicine.
Reviewer-flagged: awaiting clinical-reviewer sign-off.
CYP2C9 inhibition
Caution Does Berberine interact with Warfarin sodium?
Berberine may increase the effect of warfarin and with it your risk of bleeding, so tell whoever manages your warfarin before you start taking it. The reason for the caution is that berberine has been shown in people to slow the liver enzyme that clears the more powerful half of warfarin, which could raise your INR. No study has tested the two together in people; in one study in mice, berberine made warfarin's effect on clotting stronger. Other evidence puts berberine's effects on different enzymes, so this is a reason to keep to your usual INR checks and mention the supplement rather than a known problem. Do not stop or change your warfarin dose yourself.
Evidence: No direct study of this exact combination yet; the caution rests on a plausible mechanism or on reports involving a related medicine.
Reviewer-flagged: awaiting clinical-reviewer sign-off.
Nrf2 + CYP modulation
Caution Does Sulforaphane (Broccoli Sprout Extract) interact with Warfarin sodium?
Sulforaphane affects liver enzymes responsible for clearing warfarin (mainly CYP2C9). The direction and magnitude in humans at supplement doses are not well characterised. Tell your GP and ask whether INR monitoring should be tightened for the first few weeks.
Evidence: No direct study of this exact combination yet; the caution rests on a plausible mechanism or on reports involving a related medicine.
Reviewer-flagged: awaiting clinical-reviewer sign-off.
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.
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How the checker decides
Every result has a source
Each pair we have assessed is cited to a published study (PMID) or the British National Formulary, so you can read the source yourself.
Four kinds of answer
Severe, caution, no known interaction, and not yet assessed. A pair we have not assessed is never shown as clear.
- Severe
- Caution
- No known interaction
- Not yet assessed
Nothing in our data is not a clearance
When nothing in our data records a problem with a pair, the result says no known interaction at typical doses, which is not a clearance: your pharmacist or GP can check the pair against your full medical history.
A full supplement review, built around you, not a generic stack.
The free checker answers one interaction question at a time. A Distil report reviews the bigger picture: your goals, diet, medications, current supplements and any blood results you provide, then shows what appears worth keeping, changing, adding or leaving out.
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The interaction check is one section of the full report. You also get the reasoning behind each recommendation and the evidence references used.
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