Omega-3 Fatty Acids and Warfarin

Omega-3 fatty acid (fish oils) are a form of polyunsaturated fat that the body derives from food. Omega-3s (and omega-6s) are known as essential fatty acids (EFAs) because they are important for good health. The fatty acid has an affect on platelets making them slightly less "sticky", this has played a favorable role in preventing heart attacks and strokes.1

The benefits of fish oils do not seem to be limited to cardiac benefit. The rods and cones of the eye are a natural source of docosahexaenoic acid (DHA), a fatty acid similar to those found in fish. A deficiency of DHA in the eye has been associated with visual problems. It is speculated that supplemental DHA in capsule form or in increased fish consumption could lead to improvement in visual performance. More research is needed but preliminary work has been promising.2

Where are omega-3 fatty acids found?3

Fatty fish such as mackerel, salmon, striped bass, rainbow trout, halibut, sardines, and to a lesser extent tuna all contain omega-3 fatty acids. Other omega-3 fatty acids are found in dark green leafy vegetables, flaxseed oils, and certain vegetable oils.

Interactions with warfarin?

There have been case studies reported that show a significant elevation in INR in patients taking increased doses of fish oils. In one case a woman on 1.5mg/day of warfarin doubled her daily intake of fish oil from 1000mg/day to 2000mg/day and saw an increase on a stable INR of 2.8 to 4.3 within a 30-day period. Her INR plummeted to 1.6 after only a week of withholding the additional fish oil intake. Omega-3 fatty acids “may affect platelet aggregation and/or vitamin K-dependent coagulation factors.”4

  Increasing testing frequency is recommended when starting or stopping any dietary supplement. 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.5 Go to the Getting Started page for more information about testing your INR at home.  

  1. Kris-Etherton P, Harris W, Appel L, for the Nutrition Committee. Fish Consumption, Fish Oil, Omega-3 Fatty Acids, and Cardiovascular Disease. Arteriosclerosis, Thrombosis, and Vascular Biology. 2003; 23: e20-e30.
  2. Hodge W, Barnes D, Schachter H, Pan Y, Lowcock E, Zhang L, Sampson M, Morrison A, Tran K, Miguelez M, Lewin G. Effects of Omega-3 Fatty Acids on Eye Health. Evidence Report/Technology Assessment No. 117 (Prepared by University of Ottawa Evidence-based Practice Center under Contract No. 290-02-0021.) AHRQ Publication No. 05-E008-2. Rockville, MD: Agency for Healthcare Research and Quality. July 2005.
  3. National Institutes of Health
  4. Buckley MS, Goff AD, Knapp WE. Fish oil interaction with warfarin. Ann Pharmacother. 2004 Jan;38(1):50-2.
  5. Center for Medicare and Medicaid Services. Decision Memo for Prothrombin Time (INR) Monitor for Home Anticoagulation Management  (CAG-00087R) [Memorandum]. 2008. Baltimore, MD.