What's happening
Dong quai (Angelica sinensis) root contains natural coumarin derivatives — ferulic acid, osthole, and related compounds — with documented antithrombotic and platelet-inhibitory activity in vitro. Because warfarin itself is structurally a coumarin, adding plant coumarins is mechanistically intuitive. Animal steady-state studies show dong quai significantly increases prothrombin time WITHOUT changing warfarin blood concentration — suggesting a pharmacodynamic rather than pharmacokinetic interaction. The primary human evidence is a single case report (Page & Lawrence 1999): a 46-year-old woman stable on warfarin self-initiated dong quai 565 mg 1-2 times daily. Over 4 weeks her INR rose to 4.05 then 4.90 — more than double baseline — without bleeding events. She stopped dong quai; INR returned to acceptable levels within a month. No other changes were identified. The washout pattern strengthens attribution, but a single case cannot establish population-level effect size. Two systematic reviews list dong quai among herbs with documented warfarin potentiation. Commercial dong quai preparations vary widely in coumarin content, so 'low dose' is hard to define reliably.
Recommendation
If you take warfarin, do not start dong quai without telling your prescriber. If you already take both, don't stop abruptly — ask for an INR check and a plan to discontinue. Watch for unusual bruising, gum bleeding, nosebleeds, or dark stools. For perimenopausal symptoms (the most common reason people take dong quai), discuss alternatives that do not interact with warfarin. Stop dong quai 1-2 weeks before elective surgery.
Timing
Spacing doses does not help; the interaction is pharmacodynamic and operates on the anticoagulation endpoint, not absorption.
Sources
- — PMID:10417036 — Page RL, Lawrence JD. Potentiation of warfarin by dong quai. Pharmacotherapy 1999.
- — DOI:10.1177/1934578X1400900835 — Warfarin Interactions with Medicinal Herbs. Natural Product Communications 2014.
- — PMID:25707010 — Interaction between warfarin and Chinese herbal medicines. 2015.