What happens when you take chamomile tea with warfarin?
Chamomile (Matricaria chamomilla, also sold as German chamomile) is one of the most widely consumed herbal teas in the world, valued for its mild calming and digestive properties. Warfarin is a vitamin K antagonist anticoagulant whose own mechanism is built on the coumarin chemical scaffold. The concern when the two are combined unfolds in a few steps:
- Chamomile carries coumarin-type compounds. Chamomile contains naturally occurring coumarin derivatives such as herniarin and umbelliferone. These share the same basic chemical scaffold as warfarin and may add a mild blood-thinning effect on top of your prescribed dose.
- It may slow warfarin's clearance. Components of chamomile can inhibit the liver enzymes (notably CYP1A2, CYP2C9, and CYP3A4) that break down warfarin. When those enzymes are slowed, warfarin can linger longer and build up more than expected.
- The combined effect can nudge the INR upward. Together these mechanisms could push your INR above your therapeutic range without any change to your warfarin dose, diet, or adherence — and the shift can appear within days of starting heavy chamomile use.
The clinical signal that put this combination on the map is a single published case report. An older woman whose warfarin had been stable for a long time was admitted to hospital with severe internal bleeding and an INR far above her target range. She had recently begun drinking chamomile tea several times a day and applying a chamomile-based lotion to ease symptoms of an upper respiratory infection, while her diet, warfarin dose, and adherence had not changed.
Why is this important?
Warfarin has one of the narrowest therapeutic windows of any commonly prescribed drug. Small disturbances to its absorption, protein binding, or metabolism can push the INR out of range, and a markedly elevated INR sharply raises the risk of serious bleeding.
People taking warfarin are routinely warned about leafy greens, cranberry juice, alcohol, and over-the-counter anti-inflammatories, but herbal teas are often overlooked because they feel like food rather than medicine. Chamomile is specifically marketed as gentle and safe, which can lead people to drink it in large volumes during illness or stress — exactly the situations where they may also be taking additional medications that interact with warfarin.
It is important to keep this in proportion. The evidence for the interaction rests largely on the single case report described above, and a more recent randomized, placebo-controlled crossover trial in healthy volunteers found that chamomile taken for about a week did not significantly change prothrombin time or other coagulation markers. That does not rule out a problem in people who are already on warfarin and who may carry extra risk factors such as advanced age, multiple medications, or concurrent illness — but it does mean an occasional cup is unlikely to be the issue, while heavy or sudden changes are.
What should you do?
The practical rule is consistency: keep chamomile intake steady so your warfarin dose can be calibrated around it, and review any change with the people who manage your anticoagulation.
- Before you start or stop chamomile: call your anticoagulation clinic, doctor, or pharmacist and ask whether your monitoring should be adjusted. If you have been drinking chamomile regularly, taper gradually rather than stopping all at once — abruptly removing something that may have been raising your INR can let it drop and increase clotting risk.
- Every day while you take both: keep your chamomile intake the same from day to day, and stay alert for early bleeding signs — nosebleeds, bleeding gums, unexplained bruising, pink or brown urine, black stools, heavier-than-normal menstrual bleeding, or unusual headache or back pain.
- After any meaningful change: arrange an INR check within a week or two to confirm you are still in range, and get a same-day INR check at the first sign of bleeding rather than waiting for your next scheduled appointment.
Be alert to chamomile products you may not think of as medicine: skin lotions, mouthwashes, bath products, and combination herbal blends marketed for sleep or anxiety often contain chamomile alongside other herbs (such as feverfew or ginkgo) that can also affect bleeding.
Which specific products are affected?
The concern applies most clearly to warfarin (Coumadin, Jantoven) and to other coumarin-derivative oral anticoagulants used in some countries, such as acenocoumarol (Sintrom) and phenprocoumon (Marcumar). It is theoretically less relevant — and not formally studied — for the direct oral anticoagulants (DOACs) such as apixaban, rivaroxaban, dabigatran, and edoxaban, because those drugs are not coumarin-based.
On the chamomile side, common preparations to keep steady include German chamomile tea bags, loose-leaf chamomile, chamomile tinctures, and standardized chamomile extracts in sleep and anxiety supplements. Combination products such as Sleepytime tea, Calm tea blends, and many "nighttime" herbal blends contain chamomile as a primary ingredient. Topical and oral-care products — chamomile lotions, mouthwashes, and bath products — are worth noting too, since the case report involved a lotion used alongside the tea.
The science behind it
The interaction is supported mainly by one case report, balanced against a small controlled trial in healthy people:
- Segal R, Pilote L. Warfarin interaction with Matricaria chamomilla. CMAJ. 2006;174(9):1281-1282. A single-patient case report (human) describing an older woman on long-stable warfarin who developed severe internal hemorrhage with a markedly elevated INR after beginning frequent chamomile tea and chamomile lotion use for a respiratory infection, with no other changes to her regimen. Read it here.
- Schwartz et al. Effect of chamomile intake on blood coagulation tests in healthy volunteers: a randomized, placebo-controlled, crossover trial. Perioperative Medicine. 2023;12:49. A randomized crossover trial in healthy volunteers found chamomile tea or powder taken for about a week did not significantly alter prothrombin time or other coagulation markers — suggesting any effect is modest in people not already on an anticoagulant. Read it here.
In short: the mechanism is plausible and one real, well-documented case shows it can matter, while controlled data in healthy people show no large effect. That combination is why caution is warranted specifically for warfarin patients even though the overall evidence base is thin.
Frequently Asked Questions
Can I ever drink chamomile tea on warfarin?
An occasional cup is unlikely to cause a meaningful change. The risk is tied to heavy, daily use or to suddenly starting or stopping. If you want to drink it regularly, tell your anticoagulation clinic and keep the amount steady.
Is a single cup going to be dangerous?
Probably not. The healthy-volunteer trial found no significant change in coagulation markers, and the documented case involved frequent daily use during illness. Consistency matters more than total abstinence.
Why is it risky to stop chamomile suddenly?
If chamomile has been quietly contributing to your INR, stopping it all at once can let the INR fall and raise your clotting risk. Any change — up or down — should be made gradually and with an INR check.
Does this apply to the newer blood thinners like apixaban?
The direct oral anticoagulants (apixaban, rivaroxaban, dabigatran, edoxaban) are not coumarin-based, so the interaction is theoretically less of a concern. It has not been formally studied, so still mention any herbal use to your prescriber.
What about chamomile lotions and mouthwashes?
Do not assume topical or oral-care products are automatically safe just because they are not swallowed like tea — the original case involved a chamomile lotion used alongside the tea. Mention all chamomile products, not just the tea, to your clinic.
What bleeding signs should prompt me to act?
Nosebleeds, bleeding gums, unexplained bruising, pink or brown urine, black stools, heavier-than-usual menstrual bleeding, or an unusual headache or back pain all warrant a same-day INR check rather than waiting for your next appointment.
Key takeaways
- Chamomile and warfarin can interact through additive coumarin-type effects and possible slowing of warfarin metabolism; one published case links heavy chamomile use to severe bleeding with a dangerously high INR.
- The evidence is limited — a single case report against a healthy-volunteer trial showing no significant change — so occasional small servings are likely fine while daily heavy use is the real concern.
- Consistency beats abstinence: keep chamomile intake steady, and taper rather than stop abruptly.
- Tell your doctor, pharmacist, or anticoagulation clinic before any change, and request an INR check after one.
- Remember hidden chamomile in sleep blends, lotions, mouthwashes, and bath products.