Cranberry juice and warfarin: a case of raised INR
What it found
In one woman taking warfarin, drinking cranberry juice cocktail daily for several days was followed by a rise in her INR on two separate occasions.
This was a single case report, not a study in a group of people.
What they found
Studies in people
First INR rise
After drinking about 1.5 quarts (1420 mL) of cranberry juice cocktail daily for 2 days, her INR rose to 4.6. It had averaged 2.0 over the 4 months before, on the same weekly warfarin dose.
INR after stopping juice
Her INR was 2.3 fourteen days later, when she was not drinking cranberry juice cocktail.
Second INR rise
After drinking about 2 quarts (1893 mL) of cranberry juice cocktail daily for 3 to 4 days, her INR rose to 6.5.
INR after holding warfarin
Her INR was 1.86 after warfarin was held for 3 days, and 3.2 seven days after she resumed the weekly 56 mg dose.
Other causes ruled out
During both episodes of raised INR, no other factors were found that could have raised it, such as drug, herbal, disease or other food interactions. An objective assessment rated the interaction as highly probable.
Studies in people and animals
Earlier reports and trials
There have been several case reports of cranberry juice or cranberry sauce increasing the effect of warfarin by raising the INR. However, clinical trials looking at this interaction have not shown a significant effect on INR.
What the authors conclude
“Our case report describes INR elevations in a patient previously stable on warfarin after ingestion of cranberry juice cocktail daily for several days.”
Also in their conclusions
- They report INR elevations in a patient who had been stable on warfarin after she took cranberry juice cocktail daily for several days.
- They note that this elevation occurred on 2 separate occasions, which they say distinguishes their case from other published literature.
How it was done
The authors wanted to report a case of warfarin-cranberry juice interaction that caused an INR elevation on 2 separate occasions.
They described a 46-year-old woman who was taking a total weekly dose of 56 mg of warfarin. Her INR was measured before, during and after she drank cranberry juice cocktail daily for several days, on two separate occasions.
What it can’t tell you
- We summarised it from the abstract only.
- This is a single case report, so it cannot show that cranberry juice causes INR rises in other people on warfarin.
- It cannot show how common this interaction is or who might be affected.
Who paid
- Authors work at
- Regional Medical Center at Memphis, USA
The paper
- Title
- Warfarin-cranberry juice interaction
- Type
- Case report
- Evidence
- Studies in people · animals · lab
- Summarised from
- Abstract only
- Cite
- Hamann GL, Campbell JD, George CM (2011). Warfarin-cranberry juice interaction. The Annals of pharmacotherapy. doi:10.1345/aph.1P451PubMed 21364039DOI
Summary written 26 Sep 2026. Check it against the paper before it changes what you eat. How we summarise papers · Report an error