Warfarin
Warfarin competitively inhibits the vitamin K epoxide reductase complex 1 (VKORC1), blocking hepatic carboxylation of clotting factors II, VII, IX, and X.
Kitchen Food, Drink & Dietary Conflicts
Biochemical interactions with common foods, beverages & cooking ingredientsEat a healthy diet. Some foods and beverages that contain vitamin K can affect how warfarin works. Ask your doctor or pharmacist for a list of foods that contain vitamin K. Eat consistent amounts of vitamin K-containing food on a week-to-week basis. Do not eat large amounts of leafy, green vegetables or certain vegetable oils that contain large amounts of vitamin K. Be sure to talk to your doctor before you make any changes in your diet. Talk to your doctor about eating grapefruit and drinking grapefruit juice while taking this medication.
Grapefruit / Pomelo (Citrus paradisi / Citrus maxima)
Destroys enterocyte CYP3A4 enzymes, collapsing first-pass drug metabolism and causing up to 12-fold spikes in bioavailability for oral CYP3A4 substrates (statins, calcium channel blockers, immunosuppressants, PDE5 inhibitors).
Spinach / Swiss Chard (High-Oxalate & High-Vitamin K Greens)
Exogenous vitamin K directly reactivates hepatic clotting factor synthesis (Factors II, VII, IX, X), rapidly decreasing INR and precipitating thromboembolism or stroke in warfarin patients.
Fresh Orange Juice & Apple Juice (OATP Influx Blockers)
Unlike CYP3A4 inhibitors that increase drug levels, fruit juice bioflavonoids block the enterocyte OATP influx pumps, plummeting absorption of oral fexofenadine (Allegra), ciprofloxacin, and atenolol by 30-70%.
Alcoholic Beverages (Beer, Wine, Spirits)
Multiplies respiratory depression and profound sedation with opioids and sedatives; blocks hepatic lactate uptake with metformin (lactic acidosis); triggers acute disulfiram-like vomiting and tachycardia with metronidazole; and accelerates dose-dumping in extended-release capsules.
Prescription & OTC Drug Interactions (DDI)
Documented pharmacological conflicts & contraindicated co-prescriptionsAntiplatelet Agents (Aspirin, Clopidogrel) & NSAIDs
Mechanism: Dual impairment of primary platelet plug formation and secondary coagulation cascade carboxylation, combined with gastric mucosal ulceration.
Broad-Spectrum Antibiotics & Azole Antifungals
Mechanism: Antibiotics eradicate intestinal vitamin K-synthesizing flora; azoles (fluconazole) potently inhibit CYP2C9 clearance of S-warfarin.
Dietary Supplements, Herbs & Minerals (DNI)
Interactions with over-the-counter vitamins, minerals, and herbal preparationsSt. John's Wort (Hypericum perforatum)
Hyperforin potently activates the Pregnane X Receptor (PXR), inducing hepatic CYP enzymes and intestinal P-gp pumps. This accelerates medication clearance and precipitates therapeutic failure.
Ginkgo Biloba & High-Dose Garlic Extracts
Ginkgolides and ajoene exert independent antiplatelet properties that amplify anticoagulant therapy, increasing spontaneous mucosal, gingival, and gastrointestinal bleeding.
Chronotherapy & Meal Administration Protocols
Optimal absorption, meal-timing rules & GI tolerability protocolsFrequently Researched Drug-Substance Combinations
Explore pairwise interaction dossiers and laboratory safety analysesWarfarin and Aspirin
Pairwise Clinical Analysis & Safety RatingWarfarin and Spinach
Pairwise Clinical Analysis & Safety RatingWarfarin and Ginkgo
Pairwise Clinical Analysis & Safety RatingWarfarin and Garlic
Pairwise Clinical Analysis & Safety RatingWarfarin and Curcumin
Pairwise Clinical Analysis & Safety RatingWarfarin and Omega-3
Pairwise Clinical Analysis & Safety RatingTaking Warfarin alongside daily coffee, supplements, or other medications?
Add all your daily medications, foods (Dairy, Spinach, Coffee, Grapefruit), and botanicals (Ashwagandha, Curcumin, Melatonin) into the SafeStack interactive engine to run full multi-way synergy collision analysis in real time.
Data on this clinical monograph is compiled from the U.S. National Library of Medicine (MedlinePlus), openFDA Structured Product Labeling (SPL Section 7 Drug Interactions), the NIH Office of Dietary Supplements (ODS), and Krause and Mahan's Food & Nutrition Care Process.