Blood-thinning agents, also known as anticoagulant medications, are used to treat a number of medical conditions. These medicines prevent the formation of blood clots, which can cause a heart attack, stroke or another serious health problem. A variety of natural substances also have blood-thinning effects, including some common foods and nutritional supplements. However, these substances should not be used as a substitute for prescription anticoagulant medication.
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The authors of a March 2001 summary article published in "JAMA Internal Medicine" report that garlic has been found in some studies to exert a mild inhibitory effect on platelet aggregation -- one of the initial steps in blood clot formation. Other studies, however, have found that garlic does not have blood-thinning effects when taken alone at daily recommended doses.
The authors of a May 2013 article published in "Critical Reviews in Food Science and Nutrition" examined all of the published medical studies to date evaluating medical uses of garlic. They concluded that there is insufficient evidence to determine whether garlic may be useful for the prevention of blood clots. However, it may have blood-thinning effects when taken in large amounts or potentially boost the effects of anticoagulant medications. Further research on the potential blood-thinning properties of garlic is needed.
Fish and Fish Oil
Fish contains the omega-3 fatty acids EPA and DHA, which have been shown to have blood-thinning effects. EPA and DHA act as blood thinners by inhibiting the formation of substances that promote blood clot formation. Fish oil supplements are available in capsule and liquid forms, and dosages vary by manufacturer.
Food sources of EPA and DHA include fatty fish, such as cod, salmon, sardines, tuna and mackerel. The American Heart Association notes that research data support daily consumption of 0.5 to 1.8 g of combined EPA and DHA to lower the risk of coronary heart disease. This equates to about 2 servings of fish weekly.
Vitamin E inhibits blood clot formation through a variety of mechanisms -- at least in the laboratory. These blood-thinning effects appear to be dose dependent, meaning the effects may not be significant at low concentrations. More research is needed to determine whether there is a potential role for vitamin E as a natural blood thinner and, if so, to establish effective dosage recommendations. Vitamin E is found in a number of foods, including whole grains, wheat germ oil, almond oil, sunflower oil, egg yolks, seeds and nuts.
The commonly prescribed blood-thinning medication warfarin (Coumadin) is a derivative of a naturally occurring, plant-derived chemical called coumarin. More than 3,400 different coumarins have been found in a wide assortment of plants, fungi and bacteria. However, very few coumarins exert anticoagulant effects, which are typically very weak. It is a common misconception that coumarin-containing herbs have comparable blood-thinning effects to the medication warfarin -- which is not true. In fact, no substantial evidence supports use of plant sources of coumarin as effective, safe blood-thinning agents. Nonetheless, many doctors recommend that people on prescription blood thinners avoid coumarin-rich herbs to avoid possible additive effects. Examples include angelica root, arnica flower, anise, chamomile, fenugreek, licorice root, parsley and red clover.
Warnings and Precautions
The Centers for Disease Control and Prevention noted in 2011 that 53 percent of adults in the U.S. report using dietary supplements. Discuss your medications, supplements and dietary choices with your healthcare provider as they might interact or have additive effects when combined with blood-thinning medications. Do not stop taking your prescription anticoagulant medication or replace it with natural products without first consulting your healthcare provider.
Although many natural substances have blood-thinning and clot prevention potential, research is needed to clarify the possible interactions, effective forms and dosages before standardized health recommendations can be made for use of natural blood thinners.
Reviewed and revised by: Tina M. St. John, M.D.