Based on WHO | Is it safe to drink green tea while taking warfarin, and could it affect my INR or bleeding risk?

It can be safe to drink small, consistent amounts of green tea while taking warfarin, but larger or changing amounts may lower your INR and reduce warfarin’s effect, which could raise clotting risk; because of this, most guidance advises limiting intake and keeping it consistent if you choose to drink it. ^{[1] [2]} Green tea and some herbal teas are commonly listed as items that can interact with warfarin, so any changes in how much you drink should be discussed with your care team and followed by an INR check. ^{[1] [3]}

Why green tea matters with warfarin

• Warfarin works by blocking vitamin K, which your body uses to form clots; anything that adds vitamin K or otherwise alters warfarin’s action can change your INR. ^[4]
• Green tea may lower INR in some people, potentially decreasing warfarin’s anticoagulation effect; this is why many anticoagulation programs recommend limiting or avoiding it, especially in large amounts. ^{[5] [2]}
• Advice from major centers suggests drinking only small amounts, and doing so consistently, to avoid INR swings. Sudden increases or decreases in green tea intake can shift your INR out of range. ^{[1] [6]}

How much is “small and consistent”?

• Practical guidance often translates to 1 small cup per day or less, taken regularly rather than sporadically, though exact tolerance varies by person; the key is consistency rather than specific cup counts. ^[1]
• Very large intakes (for example, multiple cups daily or concentrated products) are more likely to affect INR; some reports note that high-volume consumption can provide enough vitamin K to matter. ^[7]

What the evidence suggests

• Clinical guidance materials consistently list green tea as a potential interaction with warfarin and recommend caution or limitation. ^{[2] [3]}
• Observational data show that frequent use of herbs, including green tea, is associated with less time in the target INR range compared with infrequent use, suggesting a real-world impact on warfarin control. ^[8]

Practical safety tips

• Keep intake steady: If you already drink green tea, do it in small, consistent amounts rather than on-and-off or in large volumes. ^{[1] [2]}
• Check your INR after any change: If you start, stop, or significantly change the amount of green tea, arrange an INR test within about a week or as advised by your clinic. ^[1]
• Watch for signs of under- or over-anticoagulation: Lower INR (too little warfarin effect) may show up as new leg swelling, chest pain, or stroke-like symptoms; higher INR (too much effect) may show up as easy bruising, nosebleeds, gum bleeding, or blood in urine/stool seek medical care urgently for concerning symptoms. ^[3]
• Be cautious with herbal blends and supplements: Herbal teas and green tea extracts or “fat-burner” products can be more concentrated and less predictable than brewed tea. ^{[3] [7]}
• Coordinate with your anticoagulation clinic: Always tell your team about all teas, supplements, and diet changes so they can guide monitoring and dose adjustments. ^{[1] [9]}

Bottom line

• Green tea can be compatible with warfarin if intake is limited and consistent, but it may lower INR and reduce anticoagulation in some people. Because warfarin has a narrow safety window, any change in green tea intake should be discussed with your care team and followed by INR monitoring. ^{[1] [2]}
• If you prefer to avoid potential interactions altogether, choosing non-herbal, non-green-tea alternatives without vitamin K influence is a reasonable option. ^[3]

Would you like help planning a consistent beverage routine and timing an INR check around any green tea you’d like to keep?