According to the National Center for Complementary and Alternative Medicine, fish oil is among the most popular dietary supplements sold in the United States. These supplements are packed with heart-healthy omega-3 fatty acids and are associated with few serious side effects. In fact, the U.S. Food and Drug Administration states that fish oil supplements are "generally recognized as safe." However, despite fish oil's reputation, it might be associated with some risks. The U.S. National Institutes of Health warn that omega-3 supplements can increase the risk of excessive bleeding if they are taken in megadoses or combined inappropriately with certain medications.
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The U.S. National Institutes of Health (NIH) and Food and Drug Administration (FDA) note that prolonged bleeding has never been documented in people taking low to moderate doses of fish oil (less than 3,000mg of docosahexaenoic acid and eicosapentaenoic acid) each day). However, NIH notes that extremely large doses of fish oil--referred to as "Eskimo" amounts--can increase the risk of hemorrhagic stroke, nosebleed or bloody urine. The NIH advises against the use of high-dose fish oil except under the supervision of a licensed practitioner.
Several factors influence fish oil's apparent anticoagulant effects. According to the NIH, fish oils decrease the aggregation of platelets, thereby prolonging bleeding time. Additionally, some studies have shown that high-dose fish oil can reduce levels of the von Willebrand factor, a critical compound involved in the blood clotting process. Fish oil might also help to break blood clots. While this effect can benefit people who have clots in blood vessels, it might inhibit the body's ability to repair a bleeding wound. Nevertheless, NIH states that these problems are rarely an issue in people taking fish oil doses within FDA recommendations.
People taking certain medications might have an increased risk of bleeding from fish oil supplements. According to the FDA, high doses of omega-3 fatty acids can increase the risk of hemorrhage for people taking anticoagulant (blood-thinning) medications such as warfarin and heparin. In theory, pain-relieving medications like aspirin, ibuprofen and naproxen should also interact with fish oil supplements. While fish oil is not necessarily contraindicated for people taking these medications, experts advise caution. A medical practitioner can provide specific dosing guidelines to reduce the possibility of a drug interaction.
The NIH does not report an increased risk of hemorrhage in people with bleeding disorders. However, people with a history of excessive bleeding might be at an increased risk of experiencing serious side effects from fish oil. Because high-dose omega-3 supplements may reduce levels of the von Willebrand factor, it could pose a threat to people with von Willebrand disease. Fish oil supplements should also be used with caution by people with hemophilia because they could trigger a severe or life-threatening bleeding episode. Women with menorrhagia (extremely heavy periods) should avoid taking high doses of fish oil except under the supervision of a health care provider.
High-risk patients can take several precautions to prevent hemorrhage and other complications associated with fish oil. The NIH advises that patients consult a physician before taking any dietary supplement, including fish oil. Woman who are pregnant or nursing should discuss the benefits and risks of fish oil with a qualified practitioner, such as an obstetrician, midwife or pediatrician. To prevent hemorrhage during or after surgery, patients should stop taking fish oil at least two weeks before a major medical procedure. Adequate precautions can prevent life-threatening complications.