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Severe· well-documented
Avoid this combination unless your prescriber explicitly approves it with appropriate monitoring.
Green tea contains vitamin K which can reduce warfarin effectiveness. Large or inconsistent intake may cause significant INR fluctuations.
Vitamin K in green tea antagonizes warfarin's mechanism of action by providing substrate for vitamin K-dependent clotting factor synthesis.
Source: Natural Medicines Database · Reviewed April 2026
Green Tea + Warfarin (Coumadin): high risk. Avoid this combination unless your prescriber explicitly approves it with appropriate monitoring. Green tea contains vitamin K which can reduce warfarin effectiveness. Large or inconsistent intake may cause significant INR fluctuations.
Vitamin K in green tea antagonizes warfarin's mechanism of action by providing substrate for vitamin K-dependent clotting factor synthesis.
Do not stop either abruptly on your own. Talk to your prescriber or pharmacist promptly — bring this page to your appointment.
Educational information only — not medical advice. Always verify with a healthcare professional.