Is Vitamin K (dietary) Safe with warfarin?
Free · No account · based on published sources including NIH ODS, FDA drug labels, and peer-reviewed literature
Maintain a consistent, balanced diet with a stable amount of vitamin K. Avoid drastic changes in dietary habits such as eating large amounts of green leafy vegetables. Do not start high-dose vitamin K supplements without consulting your doctor.
Why this interaction occurs
Vitamin K is a direct pharmacodynamic antagonist of warfarin. Fluctuations in dietary vitamin K intake, particularly from green leafy vegetables, can significantly alter INR levels and warfarin effectiveness.
Evidence
Evidence level: strong.
Data source
FDA Drug Label
Reported safety data
The FDA’s adverse event reporting system (FAERS) has received 134,328 reports mentioning warfarin. This reflects reported cases involving the medication in general — not confirmed causation, and not specific to the warfarin + supplement combination on this page.
FAERS reports are voluntary and cannot prove that a drug caused an event. Do not use report counts to assess the safety of this specific drug-supplement pair.
Frequently asked questions
Related interactions
All Vitamin K (dietary) interactions → · All warfarin interactions →
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Educational only — not medical advice.
Always confirm with your doctor or pharmacist.