Stay safe with warfarin this Christmas: NPS MedicineWise

People who take warfarin are being reminded to take the medicine safely this Christmas season, and in particular, that changes in food and drink intake can affect how warfarin works — especially vitamin K-rich foods like leafy green vegetables, and alcohol.

NPS MedicineWise clinical adviser Dr Andrew Boyden says that the anti-clotting medicine warfarin is very effective and is used every day by thousands of Australians to prevent serious blood clot-related conditions, including stroke.

“Warfarin has been around for 60 years and is a lifesaving medicine for people at risk of blood clots that can cause strokes,” says Dr Boyden.

“But if you take warfarin, it’s important to be medicinewise and understand how to keep your INR stable and reduce your risk of bleeding, which is one of the main side effects.”

INR, or International Normalised Ratio, is the test used to monitor the effects of warfarin to make sure people stay in the target range.

Warfarin can interact with many prescription and non-prescription medicines, including some herbal and natural medicines.

“It’s vital to talk to your health professional, and let them know you are on warfarin before starting any new medicines or supplements,” says Dr Boyden.

“During the holiday season, social events and travelling can mean a change in your usual routine, and this can affect your warfarin. Remember that eating a diet containing consistent amounts of vitamin-K containing food helps keep your INR steady. Keep taking your warfarin at the same time every day, and don’t skip doses or double dose.”

Foods that are rich in vitamin K can affect how well warfarin works.

“Since vitamin K is essential to our health you shouldn’t exclude foods rich in vitamin K from your diet if you’re taking warfarin. Instead, you should keep the amount of these foods in your diet consistent — that is, have about the same amount of them each week,” says Dr Boyden.

Some examples of foods high in vitamin K are broccoli (cooked), brussel sprouts, raw cabbage, gourmet lettuce and spinach.

Dr Boyden also warns that other factors including smoking, drinking alcohol (more than one or two standard drinks a day) and illness can all affect how warfarin works.

NPS MedicineWise is preparing to launch an educational program on the optimal use of anticoagulants for health professionals and for consumers in February 2013.

For more information on prescription, over-the-counter and complementary medicines (herbal, ‘natural’, vitamins and minerals) from a health professional, call NPS Medicines Line on 1300 MEDICINE (1300 633 424) . Hours of operation are Monday–Friday 9am–5pm AEST (excluding public holidays).

To learn more about warfarin, including a list of foods that can affect how warfarin works, read the “Living with warfarin” and “Interactions” information at


Independent, evidence-based and not-for-profit, NPS MedicineWise enables better decisions about medicines and medical tests. We are funded by the Australian Government Department of Health and Ageing.