MAJOR — Use With Caution
🔴 CAUTION — Major interaction between St. Johns Wort and Warfarin. Avoid unless under direct medical supervision.
Evidence level: STRONG
St. John's Wort makes Warfarin less effective by speeding up its breakdown. This could cause dangerous blood clots.
St. John's Wort induces CYP3A4, CYP2C9, CYP1A2 — all involved in warfarin metabolism. Reduces warfarin levels and INR → clot risk.
St. Johns Wort affects how your body processes Warfarin, which may change its effectiveness. Your doctor may need to adjust dosages or consider an alternative. Do not change doses on your own.
Use caution. Many botanicals affect blood clotting — ginkgo, garlic, ginger, turmeric, and dong quai all have antiplatelet activity that can amplify Warfarin. St. John's Wort can REDUCE anticoagulant effectiveness. Take at separate times and inform your prescriber about all herbal supplements. Request more frequent INR monitoring if on warfarin.
Higher risk with: older age (65+), history of GI bleeding, concurrent use of multiple blood-thinning agents, liver disease, heavy alcohol use, recent surgery.
Monitor for any unusual symptoms and report them to your healthcare provider promptly.
Ask your doctor: "Is there a safer alternative to St. Johns Wort that I can take with Warfarin?" Bring a list of ALL supplements and medications you take.
Blood thinners have narrow safety margins. Instead of St. Johns Wort, consider safer options: CoQ10 (with INR monitoring), vitamin D3, or probiotics — these have minimal anticoagulant interactions. Always inform your anticoagulation clinic about any supplements.
St. John's Wort makes Warfarin less effective by speeding up its breakdown. This could cause dangerous blood clots.
Use caution. Many botanicals affect blood clotting — ginkgo, garlic, ginger, turmeric, and dong quai all have antiplatelet activity that can amplify Warfarin. St. John's Wort can REDUCE anticoagulant effectiveness. Take at separate times and inform your prescriber about all herbal supplements. Request more frequent INR monitoring if on warfarin.
Monitor for any unusual symptoms and report them to your healthcare provider promptly.
Blood thinners have narrow safety margins. Instead of St. Johns Wort, consider safer options: CoQ10 (with INR monitoring), vitamin D3, or probiotics — these have minimal anticoagulant interactions. Always inform your anticoagulation clinic about any supplements.
Ask your doctor: "Is there a safer alternative to St. Johns Wort that I can take with Warfarin?" Bring a list of ALL supplements and medications you take.
Or browse the full interaction database (121,000+ pairs).