Chamomile and Warfarin Interaction
Yes, chamomile can theoretically interact with warfarin and may alter INR, though the clinical evidence is limited and conflicting. Based on the FDA warfarin label, chamomile is not specifically listed among botanicals that interact with warfarin, but the label does warn that botanicals containing coumarins (which chamomile contains) have potential anticoagulant effects 1.
Evidence Assessment
Guideline Recommendations
The 2021 SPAQI perioperative guidelines recommend "consider continuing" German chamomile for surgical patients, noting there are "no data to suggest any CNS effects that would interfere with anesthesia" 2. Notably, this guideline does not recommend holding chamomile preoperatively for bleeding concerns, unlike other supplements such as ginger, ginkgo, or glucosamine which are recommended to be held 2 weeks before surgery 2.
FDA Drug Label Position
The warfarin FDA label acknowledges that:
- Caution should be exercised when botanical medicines are taken concomitantly with warfarin 1
- Few adequate, well-controlled studies exist evaluating botanical-warfarin interactions 1
- Manufacturing standardization issues with botanicals make interaction assessment difficult 1
- Additional PT/INR monitoring is advisable when initiating or discontinuing botanicals 1
The label does not specifically list chamomile among high-risk botanicals but notes that botanicals containing coumarins have potential anticoagulant effects 1.
Clinical Evidence
The evidence is contradictory:
One case report (2006) described a 70-year-old woman on warfarin who developed multiple internal hemorrhages after using chamomile tea and body lotion, suggesting theoretical potentiation risk due to coumarin constituents 3
However, a 2023 randomized, placebo-controlled, crossover trial in healthy volunteers found that chamomile intake (either as tea or extract capsules) did not prolong PT or change INR 4. This was a well-designed study with 12 subjects consuming high doses (9 tea bags daily or extract capsules for 7 days)
Multiple systematic reviews (2014,2018,2021) list chamomile among herbs that may interact with warfarin, but acknowledge the evidence is primarily theoretical or based on single case reports 5, 6, 7
Clinical Recommendations
For patients on warfarin considering chamomile use:
Monitor INR more frequently when initiating or discontinuing chamomile products 8, 1
Educate patients about the theoretical risk, even though recent controlled data suggests minimal effect 3
Consider the dose and formulation: The 2023 RCT suggests that typical tea consumption may be safe, but this was in healthy volunteers not taking warfarin 4
Maintain consistent intake: If a patient is stable on warfarin while using chamomile, advise against sudden changes in consumption patterns 8
Watch for bleeding signs: Bruising, hematomas, melena, or other bleeding manifestations 8
Important Caveats
- The single case report of severe bleeding 3 occurred in 2006, but the 2023 controlled trial 4 challenges this concern
- The 2023 study was conducted in healthy volunteers not taking warfarin, so the interaction in actual warfarin users remains uncertain
- Chamomile products vary widely in coumarin content due to lack of standardization 1
- The theoretical mechanism (coumarin content) exists, but clinical significance appears minimal based on the most recent evidence 4
The most prudent approach is to monitor INR more frequently if chamomile is started or stopped in warfarin patients, but routine avoidance may not be necessary based on current evidence.