MajorAntidepressants. Other antidepressants of herbal origin×Vitamin K antagonist anticoagulants
Updated · Methodology
Mechanism
St. John's wort is a potent inducer of the CYP3A4 enzyme (and of CYP2C9 and P-glycoprotein). After 1–2 weeks it speeds up the breakdown of Warfarin and lowers its blood level, weakening its effect.
Symptoms
Drop in international normalized ratio (INR), weaker anticoagulation, risk of thrombosis and thromboembolism.
Management
Do not combine. If St. John's wort was already taken, stop it and monitor INR; the warfarin dose may need lowering after the herb is stopped.
Check the full regimen, not just this pair
Opens the checker with these two drugs prefilled. Add the rest of the regimen and recompute additive risks.
Summary of a multi-drug list →
Medicine list: everything you take in one place →
Sources
- British Journal of Pharmacology: Clinical relevance of St. John's wort drug interactions revisited (2020)– Nicolussi S, et al. Br J Pharmacol. 2020;177(6):1212-1226.