Warfarin and herb or food interactions

A homoeopathic colleague recently mentioned that a number of her patients taking Warfarin had been recommended not to eat green vegetables for fear of interactions. There are many concerns around what is safe or not safe to do when taking prescribed medications. The net result is that people may avoid the health benefits of certain foods and herbs. I have never heard a case of a drug being reduced or withdrawn because of a potential interaction. It is always the food or herb which is to be avoided. This fixes in people’s minds that prescribed medications are the first choice for treatment and all else must follow. In over 20 years of experiencing prescribing Chinese herbs to people, I have never come across a difficulty. There are some common sense precautions to take – more of which later – however, herbs (and foods, of course) are incredibly safe and gentle.

So, what is the ‘evidence’ for not eating your greens when taking Warfarin? Very little it seems. An article at Medscape discussed this very issue of interactions. It is clearly stated in this article, that interactions are generally theoretical rather than as a result of hard evidence. They are the result of in vitro testing (in the laboratory rather than with people), speculative or the result of occasional case reports. Cranberry juice is a case in point which the UK drug regulatory authority in 2004 recommended should be avoided in those taking Warfarin. This was on the basis of a very few poorly researched case reports. An analysis of this, concluding that cranberry is fine to take in average or moderate amounts can be seen here.

So, what other foods or herbs are considered to be potentially problematic? These include angelica root, arnica flower, anise, asafoetida, bogbean, borage seed, bromelain, capsicum, celery, chamomile, clove, fenugreek, feverfew, garlic, ginger, gingko, horse chestnut, licorice root, lovage root, meadowsweet, onion, parsley, passionflower, poplar, quassia, red clover, rue, sweet clover, turmeric and willow bark.

Other herbs and supplements that have been implicated include the Chinese herbs of dan shen, dang gui and ginseng as well as devil’s claw, green tea, papain, Coenzyme Q 10 and vitamin E.

Foods such as liver, leafy green vegetables and vegetable oils may contain larger amounts of Vitamin K which can reduce the effectiveness of Warfarin.

The main points here are that many supposed interactions are speculative or based on laboratory experiments and that a moderate intake of, for example, green vegetables will not pose a problem.

If a herbalist sees someone taking Warfarin it makes sense to introduce herbs slowly and gradually. This is good advice generally when using herbs in those people taking prescribed medications. Warfarin dosage is adjusted according to regular blood tests (INR – international normalized ratio ) so any slow and gradual introduction of a food or herb can be monitored. If the food or herb is of benefit to our health, then this can be taken safely with the above proviso. Don’t do anything quickly or initially in large doses.

As a general rule, any herbs given should not duplicate the effect of any prescribed drug. So, Warfarin moves and thins the blood. Any herb which also has this effect should be used with caution. However, certainly in Chinese herbal medicine, we rarely use a single herb – rather we use a formula containing a number of herbs. The issue here, therefore, is what is the action of the formula as a whole. For example, I frequently use Dang Gui (Angelica sinensis) in a formula for people taking Warfarin as the drug has the effect of weakening and heating the blood (in terms of Chinese medicine). Technically, this can affect Warfarin control but I have never seen this in practice as this herb is merely one of a dozen or more in an individualised formula.

In summary:

Most herbs and foods are safe when used with Warfarin.

Consider what the individual person needs to be healthy – diet, herbs – as you would normally.

Introduce foods and herbs, you think are of concern, slowly and in small dosages.

INR should be monitored regularly (this is the usual practice in those taking Warfarin)

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