Caffeine and Warfarin

Most think of caffeine as a stimulant that gets us going in the morning, but it appears in many beverages, foods and over the counter medications. Not only is caffeine naturally found in coffee, teas, and chocolate, it is also produced synthetically and found in tablet form, sodas, and even gum.

The U.S. Food and Drug Administration (FDA) recognizes caffeine as both a drug and a food additive is considered and "Generally Recognized as Safe" (GRAS). But, caffeine is an addictive product. Withdrawal results in distinct side effects not limited to headache. Ironically, the FDA has approved taking oral caffeine in combination with analgesics for treating simple headache.1 Caffeine and acetaminophen and aspirin is effective for treating migrane headache.2

According to the National Institutes of Health, caffeine is often associated with sleep disturbances, irritability, and anxiety. Additional side effects include: nervousness, restlessness, gastric irritation, nausea, vomiting, tachycardia, quickened respiration, tremors and convulsions.

Caffeine's traditional side effects now include the potential to alter INR levels. The 2010 Natural Medicines Comprehensive Database suggests "an increase in bleeding risk for patients on warfarin due to antiplatelet activity may occur; however, there is a lack of data on whether caffeine affects patient INR test results."

If you have questions about whether caffeine is safe for you, talk with your doctor. Increasing testing frequency is recommended when starting or stopping any new medication or dietary supplement including vitamins. Home INR monitoring will help improve your control of warfarin. More frequent testing, typically performed by patient self testing, is a valuable tool for detecting rises and falls in INR values and enable you to work with your clinician to make any adjustments to diet or medication dosing.3 Go to the Getting Started page for more information about testing your INR at home.

  1. Migliardi JR, Armellino JJ, Friedman M, Gillings DB, Beaver WT. Caffeine as an analgesic adjuvant in tension headache. Clin Pharmacol Ther. 1994 Nov;56(5):576-86.
  2. Goldstein J. Treatment of severe, disabling migraine attacks in an over-the-counter population of migraine sufferers: results from three randomized, placebo-controlled studies of the combination of acetaminophen, aspirin, and caffeine. Cephalalgia. 1999 Sep;19(7):684-91.
  3. Center for Medicare and Medicaid Services. Decision Memo for Prothrombin Time (INR) Monitor for Home Anticoagulation Management  (CAG-00087R) [Memorandum]. 2008. Baltimore, MD.