Cranberry Interactions

Cranberry juice contains flavonoids that may inhibit CYP2C9, the primary enzyme that metabolizes the active S-enantiomer of warfarin. Multiple case reports describe elevated INR and major bleeding (including fatal hemorrhage) in patients who drank cranberry juice while stably anticoagulated, though randomized trials with smaller doses have not consistently reproduced the effect.

Cranberry juice has been shown to inhibit intestinal CYP3A enzymes, and tacrolimus is heavily metabolized by intestinal CYP3A4 and CYP3A5. The expected direction is an increase in tacrolimus trough levels, raising the risk of nephrotoxicity and tremor, although published cases are scarce and one case unexpectedly reported a decrease.