Warfarin and diet - your questions answered

Published in Medicinewise Living

Date published: About this date

This page was updated 5 March 2014

Contributed by NPS Medicines Line

elderly couple

Big changes in your diet or alcohol intake could affect your INR.
Image: Ajay Bhaskar / shutterstock.com

Q: I have been taking warfarin for some time and my INR is stable. Is it safe for me to have a drink or two and to enjoy a soy latte with my wife each morning? I also take fish oil capsules and cranberry juice. Is this okay?

A: In general, even if your INR is stable, big changes in your diet or alcohol intake, especially in the amount of vitamin K-containing foods, could affect your INR.

Alcohol and warfarin

Generally, drinking small or moderate amounts of alcohol is unlikely to affect your INR if you are taking warfarin and have normal liver function. If you haven’t been drinking until now and you start having one or two drinks a day regularly when your INR (International Normalised Ratio) is stable, it is unlikely your INR will be affected. However, it would be wise to have your INR checked by your GP, because an individual's response to alcohol and warfarin can vary.

Be aware that consuming large amounts of alcohol, especially binge drinking, may increase your risk of bleeding.

As a general rule, it is best to drink only in moderation, and to limit your daily intake to no more than 1 or 2 standard drinks a day, with at least 2 alcohol-free days a week. For more information on alcohol and your health, see the Australian Government's alcohol guidelines.

Soy milk and warfarin

Food and drinks high in vitamin K can potentially affect your INR. As most soy milk products are low in vitamin K, drinking a soy latte each day is unlikely to affect your INR.

Food and beverage labels show nutritional content; however, vitamin K information is not always included. This can make it difficult for you to eat consistent amounts of vitamin K. Refer to your warfarin booklet or ask your GP or pharmacist if you are unsure.

Fish oil and warfarin

There have been cases of increased bleeding in people taking fish oil with warfarin. Diets containing salmon oil, mackerel or cod liver oil have also been reported to prolong bleeding times. This is because fish oil can decrease the 'stickiness' of the platelets in your blood, making bruising and bleeding more likely.

However, this effect of fish oil may not show up in your INR. In other words, your INR may remain stable even if your risk of bleeding is increased. So to be safe, if you take warfarin and are also taking high-dose fish oil — containing the omega-3 fatty acids, eicosapentaenoic acid (EPA), and docosahexaenoic acid (DHA) in doses over 3 g daily — you should monitor yourself regularly for bruising and other signs of increased bleeding. This is especially true for older people. Talk to your health professional if you are taking high doses of fish oil and take other anti-clotting medicines.

Cranberry juice and warfarin

Consuming up to 250 mL of cranberry juice daily poses minimal risk to people taking warfarin. A clinically significant interaction can occur when drinking larger amounts of cranberry juice each day. Doing so may increase your bleeding risk.


Warfarin, fish oil and cranberry juice — interactions

The original version of this Q&A article, published in the April 2013 Medicinewise Living email, advised that the consumption of fish oil by people taking warfarin may result in increased INRs. In fact, fish oil supplements may not affect INR results, but may still increase the risk of bleeding when taken with warfarin (because fish oil can increase your bleeding risk in other ways).

In other words, your INR may remain stable but the risk of bleeding is still increased. If you take warfarin and fish oil, you should regularly monitor for signs of increased bleeding, which may include bruising — particularly if you are taking more than 3 g daily of fish oil containing omega-3 fatty acids such as EPA and DHA.

The article also stated that "moderate consumption of cranberry juice poses minimal risk to people taking warfarin". To clarify, daily consumption of up to 250 mL cranberry juice is not known to increase the risk of bleeding in a person taking warfarin. However, it is possible that consuming larger amounts of cranberry juice when you are taking warfarin may cause a clinically significant interaction, which may increase the risk of bleeding.

For information from a health professional about medicines over the phone, call NPS Medicines Line on 1300 MEDICINE (1300 633 424 ) Mon–Fri, 9am–5pm AEST. Calls will be answered by healthdirect Australia.