Which dietary change would interfere with warfarin therapy and require provider consultation?

• A. Increase dark-green, leafy vegetables
• B. Decrease dark-green leafy vegetables
• C. Increase citrus fruits
• D. Increase dairy products

Answer: (A)

Warfarin works by inhibiting vitamin K–dependent clotting factors, so keeping vitamin K intake fairly constant is important for stable anticoagulation. Increasing dark-green, leafy vegetables raises vitamin K intake, which can counteract warfarin’s effect and lower the INR, potentially increasing the risk of clot formation. When this dietary change occurs, a provider should be consulted to monitor the INR and adjust the warfarin dose as needed. Decreasing leafy greens would enhance warfarin's effect and raise bleeding risk, while citrus fruits and dairy products generally do not cause the same level of interaction with warfarin.