What happens when you take warfarin with feverfew?
Warfarin is a vitamin K antagonist used to prevent dangerous blood clots. Feverfew (Tanacetum parthenium) is a daisy-family herb taken mainly for migraine prevention. The concern about combining them is theoretical rather than proven, and it works through two separate pathways that affect bleeding in different ways.
- Warfarin blocks the recycling of vitamin K in the liver. This slows the production of several clotting factors, which keeps the blood from clotting too easily. The international normalised ratio (INR) is the blood test used to keep this effect inside a safe window.
- Feverfew's main active constituents are sesquiterpene lactones, especially parthenolide. In laboratory studies, parthenolide can interfere with platelet aggregation by affecting serotonin release from platelets and arachidonic-acid pathways.
- Because the two substances act on different parts of the clotting system, a concern is that their effects could add up. This is a plausible mechanism, not a documented event: the antiplatelet signal for feverfew comes from bench and test-tube studies, and there are no published human reports of bleeding when feverfew is combined with warfarin.
- Importantly, any platelet effect from feverfew would not show up on the INR test, which only tracks warfarin's clotting-factor effect. So a normal INR would not, on its own, rule the herb in or out.
Why is this important?
This is a low-severity, mechanism-based caution rather than a strong-signal interaction. Feverfew is not in the same league as herbs like danshen or dong quai, where bleeding cases are actually documented. The reasons to stay cautious are modest but reasonable.
First, the population using feverfew overlaps with the warfarin population. Feverfew is most often taken for migraine prevention, and migraine sufferers may later be prescribed warfarin for atrial fibrillation or after a clot. Second, any antiplatelet effect would be invisible to the INR test, so routine monitoring would not catch it. Third, because supplement use often goes undisclosed to clinicians, the absence of case reports may partly reflect underreporting rather than proven safety.
Older adults, people who bruise easily, anyone also taking aspirin or NSAIDs, and patients with prior gastrointestinal bleeding would face the highest absolute risk if any additive effect did occur.
What should you do?
The practical approach is built around disclosure and a sensible plan, not around precise dosing.
Before any change: Tell the clinician who manages your anticoagulation that you take, or are thinking about taking, feverfew. Most will suggest avoiding concentrated feverfew supplements while you are on warfarin, and can help you choose a migraine-prevention alternative if needed.
Every day while the two overlap: If you and your clinician decide you will continue feverfew, stay alert to bleeding signs and keep taking your warfarin exactly as prescribed. Remember that a normal INR does not prove the herb is safe, because the platelet effect does not register on that test.
Around any change (starting, stopping, or dose adjustment): Ask your clinician whether an INR check makes sense after the change, and tell every surgeon and dentist about feverfew use before a procedure. Many will ask you to stop the supplement a week or two beforehand.
Stop the feverfew and contact your anticoagulation clinic the same day if you notice bleeding warning signs: a nosebleed that will not stop, bleeding gums, pink or red urine, black or tarry stools, coffee-ground vomiting, new large bruises, severe headache, or new weakness, numbness, or vision change.
Which specific products are affected?
The concern covers feverfew taken in concentrated form: dried-leaf capsules, standardised parthenolide extracts, and liquid tinctures. It also covers migraine-prevention blends that include feverfew, which often list it alongside butterbur, magnesium, riboflavin, and CoQ10. Check the herbal ingredient panel, not just the brand name.
Chewing a fresh feverfew leaf, a traditional folk migraine remedy, delivers a small but unstandardised amount and is best avoided on warfarin for the same reason. Feverfew is not used as a cooking herb, so there is no culinary-versus-supplement distinction the way there is with garlic, ginger, or turmeric.
The science behind it
The evidence base for this interaction is thin and entirely preclinical, which is why the caution is mechanism-based rather than case-based.
A literature review of the bleeding risks of dietary supplements (Hatfield et al., PMC9586694) places feverfew among supplements with bench-research support for bleeding potential and notes no clinical evidence either for or against bleeding in patients. The Merck Manual Professional Edition feverfew monograph likewise describes an antiplatelet effect and a theoretical additive bleeding risk with anticoagulants, again without documented clinical cases. No human case reports of warfarin-feverfew bleeding appear in the literature.
- Hatfield J, et al. Dietary supplements and bleeding. PMC9586694 — literature review; feverfew rated as bench-research evidence, no clinical bleeding evidence.
- Merck Manual Professional Edition — Feverfew. Monograph — describes antiplatelet effect and theoretical additive risk with anticoagulants.
Frequently Asked Questions
Has feverfew actually caused bleeding in someone on warfarin?
There are no published human case reports of bleeding from combining feverfew with warfarin. The concern rests on laboratory studies of feverfew's platelet effects, not on documented events.
Will my INR show if feverfew is affecting me?
No. The INR tracks warfarin's effect on clotting factors. Any platelet effect from feverfew would not appear on that test, which is one reason a normal INR cannot fully reassure you.
How serious is this interaction?
It is considered low severity. Feverfew is not among the herbs with documented warfarin bleeding cases, so the recommendation is cautious avoidance based on plausible mechanism rather than strong evidence of harm.
What can I use for migraine prevention instead?
Several prescription and non-drug options exist, and the right one depends on your overall health. Discuss alternatives with your physician so the choice fits alongside your warfarin therapy.
Do I need to worry about feverfew in food?
Feverfew is not used as a cooking herb, so ordinary food is not a concern. The caution applies to concentrated supplements and to chewing fresh leaves as a folk remedy.
Should I tell my dentist or surgeon I take feverfew?
Yes. Disclose feverfew before any surgery or dental procedure. Many clinicians ask patients to stop herbal supplements a week or two before a procedure.
Key takeaways
- The warfarin-feverfew concern is theoretical: feverfew's antiplatelet effect is supported only by laboratory evidence, with no human bleeding case reports.
- This is a low-severity, mechanism-based caution, not a strong-signal interaction.
- Any platelet effect from feverfew would not show up on INR testing, so a normal INR does not prove safety.
- The cautious approach is to avoid concentrated feverfew supplements on warfarin and disclose use to your clinician, dentist, and surgeon.
- Review feverfew use, and any migraine-prevention alternatives, with your doctor or pharmacist.