Medication·Interactions·Reviewed June 9, 2026
Warfarin interactions.
Warfarin has 36 documented interactions in the NutriStack database, including 7 flagged to avoid or as a serious conflict. The full interaction list is below. None of this is a substitute for your prescriber's advice.
Warfarin at a glance.
A quick, data-grounded summary. The full tables are below.
Warfarin has 36 documented interactions in the NutriStack database, including 7 flagged to avoid or as a serious conflict. The full interaction list is below. None of this is a substitute for your prescriber's advice.
Substances that interact with warfarin.
Every supplement and medication in the NutriStack database with a documented interaction with this drug, highest-severity first. Open any pair for the mechanism and sources.
| Substance | Interaction | What happens |
|---|---|---|
| St. John's Wort | Contraindicated | St. John's Wort is a potent inducer of CYP3A4, CYP2C9, and P-glycoprotein, which dramatically accelerates warfarin metabolism and reduces its plasma... details → |
| Chlorella | Conflict | Chlorella is high in vitamin K, which antagonizes warfarin's anticoagulant effect. Case report: thrombotest values exceeded therapeutic limit. details → |
| Green Tea Extract | Conflict | Green tea contains vitamin K1 which can antagonize warfarin's anticoagulant effect. Concentrated green tea extract supplements provide substantially... details → |
| Vitamin C Liposomal | Conflict | High-dose vitamin C has rare case-report evidence of reducing warfarin response, followed by rapid INR increases after vitamin C is stopped.... |
| Vitamin K1 | Conflict | Vitamin K1 (phytonadione) directly reverses warfarin's anticoagulant effect. Even small, regular doses found in multivitamins (25 mcg/day) have been... details → |
| Vitamin K2 | Conflict | Vitamin K2 directly opposes warfarin's mechanism of action. Warfarin works by inhibiting vitamin K-dependent clotting factor synthesis, so... details → |
| Vitamin K2 MK-4 | Conflict | Vitamin K2 in the MK-4 (menatetrenone) form opposes warfarin in the same way as K1 and K2 MK-7: it restores production of vitamin K-dependent... details → |
| Aspirin Low-Dose | Caution | Concurrent anticoagulant and antiplatelet therapy significantly increases bleeding risk. While sometimes used intentionally (e.g., mechanical heart... details → |
| Bee Pollen | Caution | Bee pollen has case-report evidence of potentiating warfarin. A stable warfarin patient developed an INR of 7.1 about one month after starting... |
| Berberine HCl | Caution | Berberine displaces warfarin from plasma protein binding sites and inhibits CYP2C9 (warfarin metabolism enzyme). May alter INR unpredictably. |
| Black Seed Oil | Caution | Thymoquinone, the main bioactive in black seed oil (Nigella sativa), is a competitive inhibitor of CYP2C9-mediated warfarin 7-hydroxylation.... |
| Boswellia | Caution | Boswellia serrata extracts inhibit CYP2C9, CYP3A4, and CYP2C19, the isoenzymes responsible for warfarin metabolism. Spontaneous postoperative... |
| Bromelain | Caution | Bromelain, a proteolytic enzyme from pineapple stem, inhibits platelet aggregation and has been shown to reduce thrombin-, ADP-, and... |
| Cannabis (THC-Dominant) | Caution | THC-dominant cannabis can raise INR and bleeding risk in people taking warfarin. Case reports describe supratherapeutic INR after recreational or... details → |
| Chondroitin | Caution | Chondroitin is structurally a heparan-like sulfated glycosaminoglycan and is commonly taken with glucosamine for joint pain. Combined... details → |
| Clopidogrel | Caution | Triple therapy (warfarin + clopidogrel + aspirin) or dual therapy (warfarin + clopidogrel) substantially increases major bleeding risk compared to... details → |
| Coenzyme Q10 | Caution | Coenzyme Q10 (ubiquinone) is structurally similar to vitamin K and may reduce warfarin's anticoagulant effect in some patients. Case reports... details → |
| Coenzyme Q10 Ubiquinol | Caution | CoQ10 is structurally similar to vitamin K2 (both are quinones) and may partially reduce warfarin's anticoagulant effect. Several case reports have... details → |
| Evening Primrose Oil | Caution | Evening primrose oil is rich in gamma-linolenic acid (GLA), which has documented antiplatelet activity and can prolong bleeding time. Adverse-event... |
| Fenugreek | Caution | Fenugreek aqueous extract inhibits coagulation in vitro and significantly prolongs prothrombin time. A well-documented case describes a... |
| Fish Oil | Caution | Fish oil may potentiate warfarin's anticoagulant effect through its own antiplatelet and antithrombotic properties. While moderate doses (1-2g/day)... details → |
| Garlic Extract | Caution | Garlic supplements possess antiplatelet properties that may increase bleeding risk when combined with warfarin. Several case reports have documented... details → |
| Ginger Extract | Caution | Ginger extract inhibits platelet aggregation via thromboxane synthase suppression and may potentiate warfarin. Case reports describe... details → |
| Ginkgo Biloba | Caution | Ginkgo biloba has significant antiplatelet activity that increases bleeding risk when combined with warfarin. Multiple case reports document serious... details → |
| Glucosamine | Caution | 21 spontaneous reports of increased INR with glucosamine use in WHO database. |
| Grape Seed Extract | Caution | Grape seed extract contains procyanidins that inhibit platelet aggregation and prolong APTT and PT in vitro. A case report describes a stable... |
| Ibuprofen | Caution | NSAIDs increase bleeding risk with warfarin through dual mechanisms: antiplatelet effects and GI mucosal damage. Ibuprofen also inhibits CYP2C9,... details → |
| Krill Oil | Caution | Krill oil contains the same omega-3 fatty acids (EPA and DHA) as fish oil, which reduce platelet thromboxane A2 and may prolong bleeding time. The... |
| Nattokinase | Caution | Nattokinase is a fibrinolytic enzyme that degrades fibrin directly and reduces clotting factors. Combined with warfarin, the additive effects... details → |
| Pine Bark Extract | Caution | Pine bark extract (pycnogenol) inhibits platelet aggregation and reduces thromboxane generation. Combined with warfarin, these pharmacodynamic... |
| Quercetin | Caution | Quercetin and its metabolites strongly displace warfarin from human serum albumin, which can transiently raise free (active) warfarin... |
| Resveratrol | Caution | Resveratrol inhibits CYP2C9, the main enzyme that clears the more potent S-enantiomer of warfarin, and also inhibits BCRP-mediated efflux. In animal... |
| Royal Jelly | Caution | Royal Jelly has case-report evidence of potentiating warfarin. An elderly patient with previously stable warfarin therapy developed hematuria with... |
| Saw Palmetto | Caution | Saw palmetto has been linked to coagulopathy and excessive surgical bleeding in case reports, including hematuria and intraoperative hemorrhage.... |
| Turmeric/Curcumin | Caution | Curcumin may inhibit platelet aggregation and has shown anticoagulant properties in vitro and in animal studies. When combined with warfarin, there... details → |
| Vitamin E | Caution | High-dose vitamin E may potentiate warfarin's anticoagulant effect and increase bleeding risk. Vitamin E at high supplemental doses can interfere... details → |
The full warfarin profile.
Uses, typical dosing, side effects, and the cited evidence for this medication.
Common warfarin questions.
Quick answers drawn from the tables above.
What interacts with Warfarin?
In the NutriStack database, Warfarin has 36 documented interactions. The most notable include St. John's Wort, Chlorella, Green Tea Extract, Vitamin C Liposomal, and Vitamin K1. Check any specific combination before taking it and confirm with your prescriber.
Which substances should I avoid with Warfarin?
Warfarin is flagged against 7 substances in the database, including St. John's Wort, Chlorella, Green Tea Extract, Vitamin C Liposomal, Vitamin K1, and Vitamin K2. These pairings carry a higher risk and should be reviewed with a clinician before combining.
Is it safe to take St. John's Wort with Warfarin?
NutriStack classifies the St. John's Wort and Warfarin pairing as contraindicated: St. John's Wort is a potent inducer of CYP3A4, CYP2C9, and P-glycoprotein, which dramatically accelerates warfarin metabolism and reduces its plasma levels. This can... Do not take St. John's Wort with warfarin. This is a well-established dangerous interaction. If you are currently taking both, consult your... Always confirm with your prescriber.
Check your whole stack
See how warfarin fits your supplements.
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