Beverage Interactions

Understanding how diet can affect your INR is an important aspect of living a healthy life while on warfarin. Although there is no specific "warfarin diet", it is important to pay attention to what you eat while taking warfarin as some foods and beverage can alter the effectiveness of warfarin.

After being prescribed warfarin, much of the focus is often on "dark leafy greens" and vitamin K in your diet, but beverages can also affect your INR value. For example, green and black tea have been shown to interact with warfarin and affect INR values.1,2 Other beverage examples include alcohol and grapefruit juice, both of which can alter the absorption of some medications, including warfarin.3

It is important to remain consistent with your beverage intake in order to avoid fluctuations in your INR. Your warfarin dosing can then be adjusted around your healthy diet choices. More frequent INR testing is recommended to help identify any beverage/drug interactions with warfarin.4

As always, talk to your doctor about any changes to your diet and consumption of beverages, medication or supplements.

  1. Taylor JR, VM Wilt. Probable antagonism of warfarin by green tea. Ann Pharmacother April 1, 1999 vol. 33 no. 4 426-428.
  2. Parker D, Hoffmann T, Tucker M, Meier D. Interaction Between Warfarin and Black Tea. Ann Pharmacother January 2009 vol. 43 no. 1 150-151.
  3. Jellin J.M., et al. Pharmacist's Letter/Prescriber's Letter of Natural Medicines Comprehensive Database. 7th ed. Stockton, CA: Therapeutic Research Faculty. 2005. 626-629.
  4. Heneghan C., et al. (2006). Self-monitoring of oral anticoagulation: a systematic review and meta-analysis. Lancet, 367, 404-11.