Evidence for a cranberry and warfarin interaction is conflicting, but increased INR and serious bleeding have been reported. A tacrolimus case and laboratory findings involving CYP and UGT enzymes add reasons to review concentrated cranberry products with a clinician.

Use with caution. Healthcare professional review recommended before use.

Contraindications

Use as a replacement for diagnosis or treatment of an active urinary tract infection
Regular high-dose use in people prone to calcium oxalate kidney stones

Cautions

Large amounts can cause stomach upset or diarrhea.
Cranberry contains oxalates and concentrated products may increase kidney-stone risk in susceptible people.
Cranberry products differ substantially in proanthocyanidin content.

Drug Interactions

Drug Class / Substrate	Mechanism	Severity	Source
Warfarin	Large or prolonged cranberry intake may increase anticoagulant effect, although controlled data are conflicting.	Major	Memorial Sloan Kettering About Herbs
Tacrolimus	A transplant case reported subtherapeutic tacrolimus levels during cranberry extract use.	Major	Memorial Sloan Kettering About Herbs
CYP3A, CYP2C9, and UGT substrate medicines	Laboratory studies suggest altered metabolism or transport, but human relevance is inconsistent or unknown.	Uncertain	Memorial Sloan Kettering About Herbs

This information is for educational purposes only and does not constitute medical advice. Always consult a qualified healthcare provider before using herbal medicines, especially if you take prescription medications.