Vitamin K and Warfarin interaction
Vitamin K and Warfarin: the Warfarin prescribing label flag this combination with the strongest language, such as a contraindication, a boxed warning, or an instruction to avoid it.
Do not combine without a prescriber's guidance. The label language below is the strongest FDA uses.
What the FDA labels say
Curated guidance for Vitamin K
Vitamin K reduces the anticoagulant effect of warfarin; sudden changes in intake from supplements or diet can throw off INR.
From the Warfarin (Warfarin Sodium) label · effective 2026-06-24
Polycythemia vera Vasculitis Diabetes mellitus 5.9 Endogenous Factors Affecting INR The following factors may be responsible for increased INR response: diarrhea, hepatic disorders, poor nutritional state, steatorrhea, or vitamin K deficiency.
The following factors may be responsible for decreased INR response: increased vitamin K intake or hereditary warfarin resistance.
Pharmacodynamic mechanisms for drug interactions with warfarin sodium are synergism (impaired hemostasis, reduced clotting factor synthesis), competitive antagonism (vitamin K), and alteration of the physiologic control loop for vitamin K metabolism (hereditary resistance).
The amount of vitamin K in food may affect therapy with warfarin sodium.
Advise patients taking warfarin sodium to eat a normal, balanced diet maintaining a consistent amount of vitamin K.
Taking more than these two? Interactions stack. Check your whole list at once; it stays in your browser.
Open in the checkerNot medical advice. Interaction Checker quotes FDA label text and NIH fact sheets. Whether an interaction matters for you depends on doses, timing, kidney and liver function, and other conditions. Confirm with a pharmacist or prescriber.