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Warfarin Food Interactions

Brand names: Coumadin, Jantoven

Anticoagulant (Blood Thinner)

3
High Risk
1
Moderate
🥬 Vitamin K Foods (Spinach, Kale, Broccoli, Brussels Sprouts) ⚠️ High Risk

Vitamin K directly counteracts warfarin, reducing its blood-thinning effect. Eating inconsistent amounts of leafy greens can cause dangerous swings in your INR (clotting time), increasing stroke or blood-clot risk.

How it works

Warfarin works by blocking Vitamin K-dependent clotting factors. High Vitamin K intake reverses this blocking action.

What to do: Do NOT suddenly cut out leafy greens — instead, eat a consistent weekly amount. Sudden changes cause dangerous INR fluctuations. Discuss a stable "Vitamin K budget" with your doctor.
Source: FDA Warfarin Labeling (DailyMed); NIH MedlinePlus Warfarin Drug Information
🍺 Alcohol ⚠️ High Risk

Alcohol increases warfarin's blood-thinning effect, dramatically raising the risk of internal bleeding, hemorrhage, and bruising. Even moderate drinking can push INR dangerously high.

How it works

Alcohol inhibits CYP2C9, the liver enzyme that metabolizes warfarin, leading to elevated warfarin blood levels.

What to do: Avoid alcohol entirely while on warfarin. If you do drink occasionally, limit to 1-2 drinks and notify your prescriber. Never binge drink.
Source: FDA Warfarin Patient Medication Guide; Clinical Pharmacology
🌿 St. John's Wort ⚠️ High Risk

St. John's Wort dramatically reduces warfarin levels, cutting its effectiveness in half and significantly increasing risk of dangerous blood clots.

How it works

St. John's Wort is a potent CYP3A4 and P-glycoprotein inducer that accelerates warfarin breakdown.

What to do: Do NOT use St. John's Wort while on warfarin. This is a well-documented, serious interaction. Notify your doctor immediately if you have been taking it.
Source: FDA Safety Communication on St. John's Wort; WHO Drug Information
🍊 Grapefruit / Grapefruit Juice ⚡ Moderate

Grapefruit can modestly increase warfarin levels in some patients, raising bleeding risk.

How it works

Grapefruit inhibits CYP enzymes in the gut wall, potentially increasing warfarin absorption.

What to do: Avoid or limit grapefruit and grapefruit juice. Monitor INR more closely if you consume it.
Source: NIH DailyMed; American Heart Association Drug Interaction Resources
Disclaimer: Educational purposes only. Based on FDA drug labeling and NIH MedlinePlus. Consult your pharmacist or physician before changing your diet while on medication.