Cranberry juice and warfarin

• while no specific diet is recommended for patients on warfarin, certain foods and beverages can either suppress or enhance the anticoagulation effect of warfarin
• cranberry juice contains various antioxidants including flavonoids, which are known to inhibit cytochrome P450 activity, and warfarin is predominantly metabolised by the P450 isoform CYP2C9
• although the scientific data on any interaction between warfarin and cranberry juice is weak, it is not possible to define a safe quantity or brand of cranberry juice. Therefore, patients taking warfarin should be advised to avoid this drink unless the health benefits are considered to outweigh any risks. Increased medical supervision and INR monitoring should be considered for any patient taking warfarin and a regular intake of cranberry juice
  • it is not known whether other cranberry products, such as capsules or concentrates, might also interact with warfarin. Therefore similar caution should be observed with these products

Reference

1. Aston JL, Lodolce AE, Shapiro NL. Interaction between warfarin and cranberry juice. Pharmacotherapy. 2006;26:1314–9