Food and medicine interaction

Leafy greens and other vitamin K-rich foods and warfarin (Coumadin, Jantoven)

EstablishedEvidence level: established. Shown in drug labeling or in controlled studies in people.

Last reviewed October 18, 2026

What can happen

Vitamin K works against warfarin. A sudden rise in vitamin K intake can make warfarin less effective, and a sudden drop can push the INR up.

Why it happens: Warfarin works by blocking the recycling of vitamin K, which the liver needs to make clotting factors.
At ordinary food amounts: Food amounts are the whole point here. MedlinePlus advises eating consistent amounts of vitamin K foods each week and avoiding large amounts of leafy greens and certain vegetable oils.

What to do

Keep your vitamin K intake steady from week to week rather than cutting greens out, and tell your anticoagulation clinic before a big diet change. Never adjust your warfarin dose on your own.

Never stop or change a prescribed medicine without talking to the prescriber.

Common questions

Can I have leafy greens and other vitamin k-rich foods while taking anticoagulants?

Keep your vitamin K intake steady from week to week rather than cutting greens out, and tell your anticoagulation clinic before a big diet change. Never adjust your warfarin dose on your own. Food amounts are the whole point here. MedlinePlus advises eating consistent amounts of vitamin K foods each week and avoiding large amounts of leafy greens and certain vegetable oils.