Safety Issues - Interactions between essential oils and coumadin/warfarin

Recently one of my students posted to our student/graduate group asking whether any essential oils would be contra-indicated for someone on Coumadin and I thought that this would be a good topic for the blog.

Coumadin, one of the brand names for warfarin, is an anticoagulant. Originally it was launched in 1948 as a rat poison and is in fact still available for this purpose. At first it was thought to be too toxic for human consumption, however in 1951, the failed suicide attempt of a navy recruit who had taken a large dose of rat poison led clinicians to discard dicumarol in favour of warfarin. The first clinical study with warfarin was reported in 1955. In the same year, President Eisenhower was treated with warfarin following a heart attack. In the early 1950's it was approved for use as a medication and today it is the most widely prescribed anticoagulant drug in North America. However, there is a downside, warfarin can interact adversely with a number of commonly used medications as well as some foods. It is important therefor that its use is monitored by frequent blood testing to ensure that an adequate and safe dose is being taken. There is a lot of information available on the web on coumadin (warferin) however here is a summary of some of the cautions to keep in mind.

• Warfarin is contraindicated in pregnancy.
• The only common side effect of warfarin is hemorrhage (bleeding).
• The risk may also be increased in elderly people.
• Avoid sudden changes in dietary habits. Avoid ingesting unusual increases or decreases of foods high in Vitamin K (liver, broccoli, cauliflower, cabbage, kale, spinach and other green leafy vegetables, green tea, certain vegetables, cheeses and certain vitamin supplements). It is best to avoid strictly vegetarian diets that consist of foods high in vitamin K.
• Many commonly-used antibiotics, will greatly increase the effect of warfarin by reducing the metabolism of warfarin in the body. Other broad-spectrum antibiotics can reduce the amount of the normal bacterial flora in the bowel, which make significant quantities of vitamin K, thus potentiating the effect of warfarin.
• Thyroid activity also appears to influence warfarin dosing requirements.
• Excessive use of alcohol affecst the metabolism of warfarin and people taking warfarin are often cautioned against the excessive use of alcohol.
• Many drugs interact with warfarin.
• Warfarin also interacts with many herbs and spices, both those eaten in food (e.g. ginger and garlic) and those used for medicinal purposes (e.g. ginseng and Ginkgo biloba). All may increase bleeding and brusing in people taking warfarin; similar effects have been reported with borage (starflower) oil or fish oils.St. John's Wort, sometimes recommended to help with mild to moderate depression, interacts with warfarin; it induces the enzymes that break down warfarin in the body, causing a reduced anticoagulant effect.
  

And what about essential oils?

Methyl salicylate is the component to be aware of. When it is applied topically to the skin it is absorbed transdermally without any problem, quickly finding its way into the bloodstream and once there it can potentiate the anticoagulant effect of warfarin and could cause internal hemorrhage. Methyl salicylate is a component found in many liniments, however it is also found in large quantities in the essential oils of Sweet Birch (Betula lenta) and Wintergreen (Gaultheria procumbens) both of which are composed of naturally occurring methyl salicylate at around 98 - 99%. This makes it a very easy oil to adulterate by simply adding synthetic methyl salicylate. While there are those who find these oils to be very effective in sports therapy, muscle blends etc, if you must use then, do it with great care and only over very short periods of time.

Robert Tisserand and Tony Balacs, in their book Essential Oil Safety, say

These oils should not be used in therapy, either internally or externally. Do not use if taking anticoagulants (e.g. aspirin and heparn).

Also in Essential Oil Safety, Robert Tisserand and Tony Balacs have a listing on blood clotting mentioning that both garlic and onion oils demonstrate anti-platelet activity which is essential for blood clotting. However these are not two oils that one would find in most aromatherapist's kit. They do however say that :

Anti-platelet activity is also demonstrated by eugenol and iso-eugenol and is due to an anti-prostaglandin action. It would be prudent to avoid oral administration of garlic oil, onion oil, and all eugenol-rich oils in those with blood clotting problems. This group includes people with haemophilia, liver disease, kidney disease, prostate cancer and systemic lupus erythematosus. It would be prudent for anyone taking anticoagulant drugs, such as aspirin, heparin and warfarin to avoid oral use of the same group of oils.

Note the method of use they are talking about is oral. All the other references for contra-indications for herbs and warfarin I was able to find in the reference books I have on drug-herb-vitamin interactions were also for the oral use of the herb. If you wanted to carry this over to the use of the essential oil, then it would pertain to the oral use of the essential oil. With the exception of Birch and Wintergreen, essential oils applied topically on the skin or by one of the inhalation methods should not present a problem. Oils taken internally might. Another reason why we don't recommend the internal use of essential oils unless one has had specific, extensive training in that method.

Herbs listed as having a potential interaction with warfarin by A-Z Guide to Drug-Herb-Vitamin Interactions, Schuyler W. Lininger, Jr DC, Editor in chiefr, Alan R Gaby MD, Steve Austin ND, Forrest Batz PharmD, Eric Yarnell ND, Donald J Brown ND, George Constantine, RPh, PhD :

Ginger as it has been shown to reduce platelet stickiness in test tubes. Although there are no reports of interactions with anticoagulant drugs, people should discuss it with a health-care professional if they are taking an anticoagulant and wish to use ginger.

Herbs containing Coumarin Derivatives
Although there are no specific studies demonstrating interactions with anticoagulants, the following herbs contain coumarin-like substances that may interact with warfarin (coumadin) and may cause bleeding. These herbs include dong quai, fenugreek, horse chestnut, red clover, sweet clover and sweet woodruff.

The only herb on this list that we do have an essential oil for is fenugreek and I will say that, as far as I know, none of these cautions have found their way into aromatherapy literature.

Drug-Herb-Vitamin Interactions Bible, Richard Harkness, Pharm. FASCP & Steven Bratman, MD information on herbs for which we have essential oils:

Ginger - possible harmful interaction.
The herb ginger is used for nausea associated with motion sickness, morning sickness in pregnancy and the postsurgical period. Ginger appears to thicken the blood by interfering with the ability of blood platelets to clump together. As with feverfew, this raises the concern that ginger might increase the risk of abnormal bleeding when taken with warfarin (coumadin). However, there is no evidence at present that the blood-thinning effect of ginger is significant in humans. Though an additive effect of ginger and warfarin appears to be theoretical based on current evidence, it may be best to avoid this combination except under medical supervision. Ginger flavored drinks should not present a problem, but candies containing whole dried ginger are potentially of concern.
St. John's Wort - possible harmful interaction
The herb St. John's wort is primarily used to treat mild to moderate depression. Evidence suggests that St. John's wort may interfere with warfarin, possibly requiring an increased dosage of the drug to maintain the proper therapeutic effect. Seven cases have been reported in which the blood thinning effects of warfarin have been impaired in individuals taking St. John's wort. A 'hidden' risk lies in this type of interaction. Suppose your physician has raised the warfarin dose to take into account the effect of St. John's wort in holding down drug levels. if you then stop taking the herbal product, it would be like releasing the brakes, and your warfarin levels could surge dangerously high. For these reasons, if you take warfarin, avoid St. John's work except under a physician's supervision.