What happens when you take warfarin with feverfew?
Warfarin is a vitamin K antagonist. By blocking vitamin K recycling in the liver, it slows production of clotting factors II, VII, IX, and X. The international normalised ratio (INR) is the laboratory measure used to keep the anticoagulant effect inside a safe window, usually 2.0-3.0.
Feverfew (Tanacetum parthenium) is a daisy-family herb traditionally used for migraine prevention. Its main active constituents are sesquiterpene lactones, especially parthenolide. In laboratory studies, parthenolide inhibits platelet aggregation by interfering with serotonin release from platelets and with arachidonic-acid pathways. The effect is mild compared with aspirin, but it is real in vitro and has been reproduced in some human volunteer studies.
Unlike dong quai or danshen, there are no robust case reports of feverfew causing a documented bleed in a warfarin patient. The concern is therefore theoretical: feverfew has a pharmacologically plausible antiplatelet effect, warfarin already reduces clotting capacity, and the two together could plausibly add up. Standard anticoagulation references including the StatPearls Warfarin Drug Interactions chapter and the Australian Prescriber review on complementary medicines list feverfew among the herbs to avoid or monitor in patients on warfarin, on the strength of mechanism rather than published case bleeding events.
Why is this important?
The risk profile here is different from the strong-signal herbs. Feverfew is not in the same league as danshen or dong quai in terms of documented bleeding cases. But three things make caution worthwhile.
First, the population using feverfew overlaps heavily with the warfarin population. Feverfew is most commonly taken for migraine prevention, and migraine sufferers as they age may end up on warfarin for atrial fibrillation or after a venous clot. Second, antiplatelet effects are invisible to the INR test, so a normal INR does not rule out an interaction. Third, the absence of case reports may partly reflect underreporting; supplement use is often not disclosed to clinicians, and small INR shifts or minor bruising rarely make it into the literature.
Older adults, people who already bruise easily, anyone on aspirin or NSAIDs at the same time, and patients with prior gastrointestinal bleeding face the highest absolute risk.
What should you do?
If you take warfarin and use feverfew, tell the clinician who manages your anticoagulation. Most will recommend stopping the feverfew. Alternatives for migraine prevention include prescription medications such as topiramate, propranolol (with appropriate clearance for atrial fibrillation patients), CGRP inhibitors, and lifestyle measures; your physician can help choose one that fits.
If you and your clinician decide to continue feverfew, ask for an INR check within 1-2 weeks of any dose change. Plan another check 2-4 weeks later once the dose is steady. Remember that INR will not catch the platelet effect, so the absence of an INR change does not prove the herb is safe.
Stop the feverfew and contact your anticoagulation clinic the same day if you notice any of the standard bleeding warning signs: a nosebleed lasting more than 10 minutes, bleeding gums when brushing, pink or red urine, black or tarry stools, coffee-ground vomiting, new large bruises, severe headache, or new weakness, numbness, or vision change. These warnings apply to any combination of warfarin and an antiplatelet substance.
Tell every surgeon and dentist about feverfew use. Many will ask you to stop the supplement 7-14 days before a procedure.
Which specific products are affected?
The interaction concern covers feverfew taken in concentrated form: dried-leaf capsules, standardised parthenolide extracts, liquid tinctures, and migraine-prevention blends that include feverfew. Combination herbal products for headache often list feverfew alongside butterbur, magnesium, riboflavin, and CoQ10. Check the herbal ingredient panel, not just the brand name.
Eating a fresh feverfew leaf, a traditional folk remedy used by some migraine sufferers, delivers a small but unstandardised dose; this is unwise on warfarin for the same reason capsules are. 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 bottom line
Feverfew has a plausible antiplatelet mechanism through parthenolide. Documented warfarin-feverfew bleeding cases are scarce, but anticoagulation guidelines recommend avoiding the combination. Stop feverfew or work with your clinician on an alternative migraine plan. If you keep using feverfew, get INR checks after any change and treat any unusual bleeding as urgent. Always disclose feverfew use to surgeons and dentists.