Cranberry juice and warfarin blood thinner interaction in one woman
What it found
A woman taking the blood thinner warfarin had large jumps in her blood clotting test after drinking cranberry juice for a few days.
This happened to her on two separate occasions.
What they found
Studies in people
Blood clotting test jumped
Her usual test score was around 2.0. After drinking about 1420 mL of cranberry juice cocktail daily for 2 days, it rose to 4.6. Fourteen days later, without the juice, it dropped back to 2.3.
Second jump in test
Three months later she drank about 1893 mL of cranberry juice cocktail daily for 3 to 4 days. Her test score climbed to 6.5. It fell to 1.86 after pausing warfarin for 3 days.
No other causes found
During both episodes, doctors found no other drugs, herbs, illnesses or foods that could explain the higher scores. A formal check rated the link between the juice and the change as highly probable.
What the authors conclude
- They describe a patient whose blood clotting test scores rose after drinking cranberry juice cocktail daily for several days.
- Their report notes this happened on two separate occasions, which sets it apart from earlier published cases.
How it was done
Warfarin is the most commonly used blood thinner for long term treatment. Other reports have linked cranberry products to changes in how warfarin works, but clinical trials have not confirmed this effect.
Doctors followed a 46 year old woman who took 56 mg of warfarin each week. They tracked her blood clotting levels over several months as she drank large amounts of cranberry juice cocktail on two different occasions.
What it can’t tell you
- We summarised it from the abstract only.
- This is a report about one person, so it cannot show what would happen to everyone who drinks cranberry juice while taking warfarin.
- Clinical trials mentioned by the authors did not find a significant effect, so scientists do not yet know if this happens broadly.
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
- 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 30 Sep 2026. Check it against the paper before it changes what you eat. How we summarise papers · Report an error