Diet and Warfarin
By Dr Graham Stuart
I am on warfarin. Is there any food or drink that I cannot take? I have
heard that I should not drink cranberry juice as it interferes with
warfarin in some way. Also, how much alcohol is it safe for me to drink
Warfarin is an extremely useful drug that prevents the formation of
blood clots. This is necessary for patients who have an artificial
heart valve, a history of blood clots, pulmonary hypertension or who
have undergone a Fontan operation. However warfarin has a 'narrow
therapeutic margin'. This means that any change in the amount of
warfarin in your bloodstream may change the way warfarin affects you.
Thus, too much warfarin can cause excessive bleeding, while too little
reduces the drug's ability to prevent clots. Certain drugs, natural
health products (such as herbal remedies and vitamins) and foods change
the level of warfarin in the bloodstream.
Many drugs interact with warfarin. It is wise to ask the
pharmacist (or your cardiologist/GP) if there is a warfarin interaction
before starting any new drug. Common drugs that can cause this include
antibiotics, analgesics/anti-inflammatories, antidepressants and
Certain foods and 'natural' health products can affect warfarin
levels. Some increase the level (for example: ginko bilboa) while
others reduce the warfarin effect (ginseng). Vitamin K, in particular,
decreases the effect of warfarin. There are large amounts of vitamin K
in certain foods such as liver. broccoli. brussels sprouts, and green
leafy vegetables such as spinach, coriander and cabbage.
The interaction between alcohol and warfarin is complex.
Alcohol acts as a mild anticoagulant. It also can affect the metabolism
of the liver, which s important tor metabolising warfarin. As a rule of
rhumb, two to three drinks per day - glasses of wine. beer etc
-(typical cardiologist input) are unlikely to affect your warfarin
levels. Intermittent binge drinking (typical medical student input)
leads to an increase in INN (international ratio, the measurement used
to check warfarin levels in the blood) due to warfarin being
metabolised more slowly. Chronic heavy alcohol intake (Harley Street
cardiologist input just joking!) results in a lower warfarin level
because the alcohol increases the metabolism of warfarin.
Natural health products/ supplements that affect warfarin levels or blood clotting
Here is a list of foods and natural health products which affect
warfarin levels or which have an intrinsic effect on blood clotting.
This list is not exhaustive. If you take warfarin, you should avoid
sudden changes in your daily intake of these foods.
You can minimise your risk of warfarin interactions by taking your
warfarin medication at the same time each day and testing your blood
regularly (ideally with a home monitor). Talk to your doctor or
pharmacist before trying any new 'natural' remedies or supplements.
If you are already taking one of these products and warfarin, do not
change your routine unless you have discussed it with your health
professional, and go easy on the foods that affect warfarin.
Finally, if you have any unusual bruising or bleeding. contact your health care professional for advice right away.
chondroitin plus glucosamine
coenzyme 010 - also known as ubiquinone, ubidecarenone
danshen (salvia miltiorrhiza)
devil's claw (harpagophytum procumbens)
dong quai -- also known as danggui. Chinese angelica (angelica sinensis)
feverfew (tanacetum parthenium)
fenugreek together with boldo (peumus boldus)
fish oil supplements that contain eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA)
ginseng (panax ginseng) - also known as Asian ginseng. Chinese ginseng. Japanese ginseng, Korean ginseng
American ginseng (Panax quinquefolius)
green tea (camellia sinensis)
horse chestnut (aesculus hippocastanum)
lycium barbarum also known as Chinese wolfberry, Di GU Pi, Goji berry. Gou Qi Li
papaya extract (containing papain)
certain brands of quilinggao - also known as 'essence of tortoise shell'
St. John's Wort (hypericum perforatum)
wintergreen (used on the skin) - also known as methyl salicylate
Foods that affect warfarin or blood clotting
seaweed (sushi wrap)
soy protein products (including soymilk and tofu)
Dr Graham Stuart is a GUCH Consultant at Bristol Royal Infirmary.
Printed in GUCH News - Winter 2005