Can Chamomile Interact With Blood Thinners?
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Chamomile is one of the gentlest, most widely used sleep aids, which is exactly why a documented case of a serious interaction with warfarin is worth knowing about if you’re on blood-thinning medication.
Quick Answer
Chamomile contains natural coumarin compounds that can add to the blood-thinning effect of warfarin. A published case report describes a 70-year-old woman on warfarin whose INR (a measure of blood-clotting time) rose from a therapeutic 3.6 to a dangerous 7.9 after heavy chamomile use (multiple cups of tea daily plus topical chamomile lotion), resulting in internal bleeding that required hospitalization and transfusion.
What Happened in the Case Report
Published in CMAJ (Canadian Medical Association Journal), the case involved heavy chamomile use, 4 to 5 cups of tea per day plus topical chamomile lotion applied multiple times daily, in a woman on long-term warfarin for a mechanical heart valve. Her INR climbed to 7.9 (a therapeutic range is typically 2–3 for most warfarin indications), and she developed a large retroperitoneal hematoma and bilateral muscle bleeding, requiring transfusions and hospitalization. She stabilized after her warfarin dose was adjusted and chamomile was stopped.
The Mechanism
Researchers identified coumarin compounds in chamomile as the likely driver, working alongside warfarin’s blood-thinning action rather than through a major metabolic interaction. Chamomile also showed weak inhibition of CYP2C9, the enzyme that helps clear warfarin’s active form, which may have contributed. This was documented as the first reported case of a chamomile-warfarin interaction of this severity.
What This Means for Typical Use
The reported case involved unusually heavy, sustained use of both oral and topical chamomile at the same time, not an occasional cup of tea. Still, anyone on warfarin or another blood thinner should mention regular chamomile use (tea, supplements, or topical products) to the doctor managing their anticoagulation, since even smaller regular amounts could contribute to the same underlying mechanism.
Bottom Line
An occasional cup of chamomile tea is unlikely to be an issue for most people, but this is a documented, named interaction with a specific, serious outcome. If you’re on warfarin or another blood thinner, treat regular chamomile use as something your prescribing doctor should know about.
Frequently Asked Questions
Q: Does this only apply to chamomile tea?
A: No, the case involved both oral tea and topical lotion, suggesting the concern isn’t limited to one form of chamomile.
Q: Are other blood thinners affected the same way?
A: The best-documented case involves warfarin specifically; if you’re on a different anticoagulant, ask your doctor rather than assuming the same risk profile applies.
Related Reading
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- Can You Take Panax Ginseng With Blood Thinners?
- Supplement Safety & Recalls: Recent FDA and Health Canada Actions