Interaction Between Warfarin and Cranberry Juice

Jonathan L. Aston, BS; Amy E. Lodolce, PharmD; and Nancy L. Shapiro, PharmD


Pharmacotherapy. 2006;26(9):1314-1319. 

In This Article


Evidence supporting most drug interactions is often derived from case reports, which has limitations, including publication bias and an inability to prove causal relationships. However, they frequently help in identifying adverse events and drug interactions that may be otherwise overlooked.

Together, case reports substantiate the likelihood that a clinically significant interaction can occur when patients taking warfarin drink large amounts of cranberry juice. Long-term consumption of large volumes of the juice can potentially amplify destabilization of warfarin therapy. Therefore, patients receiving anticoagulation with warfarin should be informed to reduce or eliminate concomitant ingestion of cranberry juice until additional data become available. Given that patients with recurrent urinary tract infections may tend to have excessive intake of cranberry juice, they especially should be cautioned about an impending interaction. In addition, careful and frequent monitoring of the INR and of signs and symptoms of bleeding is warranted when concurrent consumption does occur, and dosages should be adjusted accordingly.

Extensive patient education regarding the ramifications of inconsistent dietary habits and fluctuations in drug use is imperative to achieve stable and effective anticoagulation with warfarin. In patients taking warfarin, an interaction may occur if they increase their intake of cranberry juice or occasionally ingest a large volume; however, small amounts of the juice are not expected to cause such an interaction.


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