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St Johns Wort × Warfarin

CRITICAL INTERACTION — Well-Established Evidence

⚠️ Mechanism

St. John's wort induces CYP2C9 and CYP3A4, increasing warfarin metabolism.

📋 Effect

Reduced anticoagulant effect; subtherapeutic INR

💊 Management

Avoid combination. If used, monitor INR frequently and adjust warfarin dose.

Plain Language Summary

This combination is dangerous because St. John's Wort can make warfarin much less effective. It causes your body to break down the medication too quickly, which may increase your risk of blood clots.

Source

Jiang X et al. Clin Pharmacol Ther 2004

Supporting Research

The effect of Hypericum perforatum on postmenopausal symptoms and depression: A randomized controlled trial PMID:31331546 DOI:10.1016/j.ctim.2019.05.028 2019
Hypericum extract LI 160 and fluoxetine in mild to moderate depression: a randomized, placebo-controlled multi-center study in outpatients PMID:15538592 2005
[Hypericum perforatum extract in treatment of mild to moderate depression. Clinical and pharmacological aspects] PMID:12212522 2002
Hypericum perforatum versus fluoxetine in the treatment of mild to moderate depression PMID:12008860 2002
Efficacy of continuation treatment with hypericum perforatum in depression PMID:12019675 2002
Predicting stable treatment response in patients with major depression treated with hypericum extract WS 5570/5572 PMID:16189745 2005
Adverse Event Profile: St Johns Wort 0
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Medical Disclaimer: This interaction record is for informational and educational purposes only and does not constitute medical advice. Drug-supplement interactions can be dangerous. Always consult your healthcare provider or pharmacist before combining any supplement with prescription medications. Do not stop or change any medication without professional guidance.