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Hypericum perforatum
Severe· well-documented
Avoid this combination unless your prescriber explicitly approves it with appropriate monitoring.
St. John's Wort decreases warfarin effectiveness by increasing its metabolism, potentially leading to subtherapeutic INR levels and increased risk of blood clots.
Induction of CYP2C9 and CYP3A4 enzymes accelerates warfarin metabolism, reducing anticoagulant effect.
Source: Natural Medicines Database · Reviewed April 2026
St. John's Wort + Warfarin (Coumadin): high risk. Avoid this combination unless your prescriber explicitly approves it with appropriate monitoring. St. John's Wort decreases warfarin effectiveness by increasing its metabolism, potentially leading to subtherapeutic INR levels and increased risk of blood clots.
Induction of CYP2C9 and CYP3A4 enzymes accelerates warfarin metabolism, reducing anticoagulant effect.
Do not stop either abruptly on your own. Talk to your prescriber or pharmacist promptly — bring this page to your appointment.
Educational information only — not medical advice. Always verify with a healthcare professional.