Fish Oil Doesn’t Cause Bleeding


Fish oil helps prevent blood from getting too sticky and forming clots (coagulating), but it doesn’t cause excessive bleeding and studies show that it doesn’t interfere with anti-coagulant medications.

In a randomized, placebo-controlled, double-blind clinical trial (the gold standard), researchers studied the effects of different doses of fish oil in patients taking warfarin, a drug that prevents blood from clotting. In addition to anti-coagulant medication, participants also received either six grams of fish oil, three grams of fish oil, or a placebo every day for four weeks. Researchers monitored clotting time using a test called the International Normalized Ratio or INR and found no difference between any of the groups. The highest dose (six grams per day) had the same effect on blood clotting as no fish oil at all.

Another randomized, placebo-controlled, double-blind study followed patients who took fish oil or a placebo (soybean oil) for five days after major abdominal surgery. Researchers found no difference in bleeding risk between the two groups but there was a difference in the length of hospitalization. People taking fish oil had shorter hospital stays and checked out, on average, almost five days sooner than those taking the placebo.

Fish oil may not cause bleeding but it can prolong bleeding by inhibiting the clotting process. It’s safe to take just after surgery, but you should avoid taking it just before surgery. Stop taking fish oil at least 48 hours before any medical procedure that carries an increased risk of bleeding. If the procedure goes well, you can resume it as soon as your doctor allows.


Bender N.K. et al. 1998. Effects of Marine Fish Oils on the Anticoagulation Status of Patients Receiving Chronic Warfarin Therapy. Journal of Thrombosis and Thrombolysis 5(3):257-261.

Gerster H. 1998. Can adults adequately convert alpha-linolenic acid (18:3n-3) to eicosapentaenoic acid (20:5n-3) and docosahexaenoic acid (22:6n-3)? International Journal of Vitamin and Nutrition Research 68(3):159-73.

Harris W.S. Expert opinion: omega-3 fatty acids and bleeding-cause for concern? American Journal of Cardiology 99(6A):44C-46C.

Wichmann M.W. et al. 2007. Evaluation of clinical safety and beneficial effects of a fish oil containing lipid emulsion (Lipoplus, MLF541): data from a prospective, randomized, multicenter trial. Critical Care Medicine 35(3):700-6.

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