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Is there a safe, natural alternative to warfarin (brand name Coumadin)?

Marie B. Walker
Henry I. Bussey, Pharm.D., FCCP, FAHA
Ann K Wittkowsky, PharmD, CACP, FASHP, FCCP
May, 2007

We often get emails at ClotCare from warfarin (Coumadin) patients wanting to know if there is a safe, natural alternative to warfarin. This question raises several issues:

  1. Does natural = safe?
  2. Is warfarin really all that un-natural?
  3. Are there alternatives to warfarin that can be used to prevent blood clots?

Does natural = safe?

There are many dietary supplements and herbal remedies available for sale in the US that claim to be "all natural and safe." This marketing slogan has been used so much that many people believe that if something is "all natural" it must be safe. Although certain natural products may have health benefits, natural products are not always safe. In fact, they can be dangerous. For example, the following substances are "natural" but many people would agree they are also dangerous: tobacco, marijuana, and poison ivy. Another example is the daffodil flower. The bulbs of these pretty flowers have a substance that affects the nervous system and can alter vision and heart rate if you eat the bulbs. The foxglove plant produces pretty flowers, but a tea made from the leaves can have beneficial or deadly affects on the heart depending on the amount consumed. South American Indians used to chew on cocoa leaves and got the effects of cocaine, clearly a dangerous substance. The list of examples could go on and on, but hopefully you get the point: natural does not necessarily mean safe.

Products marketed as dietary or herbal supplements in the U.S. are not subject to the same rigorous FDA review as are prescription medications.1 Consequently, the manufacturers of "natural" products often make claims for which there is no scientific evidence. In some cases, clinical trials will be cited, but upon closer review, these studies are often poorly designed and the results unreliable. Additionally, there is no systematic way to monitor use of "natural" products once they are on the market. Continued, systematic review of medications in use is important. One example is the medication Vioxx. Vioxx made it through the FDA's approval process, but because FDA approved medications continue to be studied even after they are available for sale, it was discovered that Vioxx had dangerous and potentially deadly side effects that had not been recognized previously. As a result, Vioxx was removed from the marketplace. There is no system in place to do the same for "natural" products, so dangerous side effects of natural products can go undetected.

Further, studies have shown that in some cases, herbal supplements or "natural" products do not always contain what the label claims they contain. There are no regulations that need to be followed to assure that what the label states is actually in the product. In some cases, herbal supplements have been shown to contain many times the labeled amount of an ingredient or none of a labeled ingredient at all. Additionally, one study published in the Journal of the American Medical Association (JAMA) found some natural products to contain toxic levels of heavy metals2.

Some manufacturers of dietary supplements attempt to avoid the problems of inconsistency in supplement contents and toxic contamination by following voluntary standards for production. Supplements labeled with the USP (U.S. Pharmacopeia) verified logo have been shown to:

  1. contain the ingredients shown on the label in the designated amount or strength
  2. not contain harmful levels of contaminants
  3. be able to be absorbed and released into the body
  4. have been made according to Good Manufacturing Practices

You can learn more about the USP Dietary Supplement program at

One additional concern raised by the use of "natural" products is that dietary supplements can interact with prescription medications and cause serious side effects.

The bottom line is that although "natural" products may have some health benefits, they are poorly studied, poorly understood, and poorly monitored. Even products that have been USP verified may be dangerous. Especially if you are on warfarin (brand name Coumadin), you should talk to your doctor before starting any dietary supplement or natural remedy.

Is warfarin really all that un-natural?

Although warfarin is made in a laboratory, it was actually first discovered in nature. In the 1950s, some ranchers in Wisconsin were troubled by the fact that their cattle were bleeding to death. The ranchers sought help at the University of Wisconsin. Researchers at the University of Wisconsin discovered that the cattle were bleeding to death as a result of eating spoiled sweet clover. The researchers at the University of Wisconsin were able to identify and isolate the substance in the spoiled sweet clover that was causing the excessive bleeding. This substance was a derivative warfarin. Thus warfarin is a substance that was identified in nature but has been modified and standardized in a laboratory to make it safe for use by individuals who want to take advantage of its benefits. When managed appropriately, warfarin is very effective at preventing blood clots and the bleeding risk is low.

Are there alternatives to warfarin that can be used to prevent blood clots?

Currently, the only alternatives to warfarin available in the US are medications that must be injected or provided intravenously. Examples include heparin and low molecular weight heparin. Brand name low molecular weight heparin products include Lovenox, Innohep, and Fragmin.

There are no "natural" alternatives to warfarin or warfarin-like medications* that have been scientifically shown to have benefit. One substance that gets a good bit of attention is nattokinase. Nattokinase is a substance found in a common Japanese food called natto, which is made of fermented soybeans. Nattokinase has been shown to have some anti-clotting characteristics, but there is no good scientific data to show that it is safe and effective when used in humans. Stephan Moll, MD of the University of North Carolina addresses the issue of nattokinase quite nicely on the FVL Support website.

In recent years, there has been a good deal of development among drug companies in this field. Many warfarin alternatives are currently being studied and may be available for sale in the next few years. However, the first new anticoagulant drug to actually reach the market had a short product life. A drug company called AstraZeneca developed an anticoagulant called ximelagatran (brand name Exanta), which became available for sale in Europe in 2004. However, in October of 2004, the FDA decided not to approve Exanta for use in the United States due to concerns that the drug caused liver toxicity and perhaps increased the risk of heart attacks. By February of 2006, AstraZeneca decided to withdraw Exanta from the European market, too.

Currently, there are about 20 other new anticoagulant drugs being developed. Only time will tell if any of these new medications will offer better protection against clotting than warfarin without posing additional health risks (such as the liver toxicity seen with Exanta).

*Phenprocoumon and acenocoumarol are two warfarin-like medications available in several countries but not available in the United States.


  1. Marder VJ. The interaction of dietary supplements with antithrombotic agents: scope of the problem. Thromb Res. 2005;117(1-2):7-13; discussion 39-42. Epub 2005 Aug 1.

  2. Saper RB, Kales SN, Paquin J, et. al. Heavy metal content of ayurvedic herbal medicine products. JAMA. 2004 Dec 15;292(23):2868-73.
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