coumarin
5 interactions related to coumarin
warfarin + dong quai
Dong quai (Angelica sinensis) contains coumarin derivatives (ferulic acid, osthole) and has documented antiplatelet activity. A widely cited case report (Page & Lawrence, Pharmacotherapy 1999, PMID 10417036) described a woman whose INR rose to 4.9 within four weeks of adding dong quai 565 mg once to twice daily to stable warfarin.
metformin + cinnamon
Cinnamon (particularly cassia and ceylon varieties) has a mild antiglycemic effect that can produce an additive blood sugar reduction when combined with metformin. The effect is modest in most studies but can become clinically meaningful in patients with already well-controlled A1c or those on combination diabetes regimens.
cinnamon + warfarin
Cassia cinnamon contains coumarin, a natural compound with anticoagulant activity that may potentiate warfarin and increase bleeding risk. Case reports describe elevated INR and bleeding when cinnamon supplements were added to stable warfarin therapy.
fenugreek + warfarin
Fenugreek (Trigonella foenum-graecum) contains coumarin-related compounds and has documented in vitro anticoagulant activity. A published case report describes elevated INR when boldo-fenugreek was added to stable warfarin therapy, with INR normalizing on discontinuation and rising again on rechallenge.
chamomile tea + warfarin
Chamomile contains coumarin-like compounds that may potentiate warfarin's anticoagulant effect. A published case report described a 70-year-old woman on stable warfarin who developed retroperitoneal hemorrhage with an INR of 7.9 after using chamomile tea and lotion for upper respiratory symptoms.