Feverfew-Anticoagulant Bleeding Risk Calculator
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A 36-year-old woman on feverfew supplements developed dangerously high bleeding times. Her prothrombin time (PT) was 27.3 seconds-more than double the normal range of 11-16 seconds. After stopping feverfew for four months, her blood clotting returned to normal. This case, documented by the NIH in 2021, shows why understanding the bleeding risk between feverfew and anticoagulants is critical.
What is feverfew and how is it used?
Feverfew (Tanacetum parthenium) is a perennial herb in the Asteraceae family, related to ragweed and daisies. For centuries, people have used it to treat migraines, inflammation, and fever. Modern research shows its active compound, parthenolide, works by blocking serotonin-induced platelet aggregation. This means feverfew can interfere with blood clotting. The Memorial Sloan Kettering Cancer Center (MSKCC) 2023 monograph states that feverfew is commonly available as dried leaf capsules (standardized to 0.2-0.7% parthenolide), liquid extracts, or fresh leaves. Typical doses for migraine prevention range from 50-300mg daily.
It's part of the 'Few Gs' mnemonic-a group of herbs including ginger, ginkgo biloba, garlic, and ginseng that may increase bleeding risk when combined with anticoagulants. This mnemonic was first proposed in a 2003 study by Ciocon and colleagues, later documented in a 2021 NIH case report.
How feverfew affects blood clotting
Feverfew's main effect on blood clotting comes from parthenolide. This compound specifically inhibits platelet aggregation triggered by serotonin. Unlike some blood thinners, feverfew doesn't affect aggregation from ADP or thrombin, making its mechanism more targeted. However, it also inhibits several cytochrome P450 enzymes (CYP1A2, 2C8, 2C9, 2C19, 2D6, and 3A4). This is crucial because many anticoagulants like warfarin rely on these enzymes for metabolism. When feverfew blocks CYP3A4 and CYP2C9, warfarin levels can rise in the blood, increasing bleeding risk.
Research from the Restorative Medicine monograph (2022) confirms feverfew's antiplatelet effects. In vitro studies show it can increase bleeding time by 20-30% when combined with anticoagulants. While this doesn't always translate to real-world cases, the potential for interaction is significant enough to warrant caution.
Real-world cases and documented risks
The NIH case report from 2021 details a woman who experienced severe coagulopathy after taking feverfew. Her PT was 27.3 seconds (normal 11-16), PTT 42 seconds (normal 18-28), and hemoglobin 10 g/dL (normal 12-15.5). After stopping feverfew for four months, her levels normalized. This case highlights how quickly feverfew can disrupt clotting.
EBSCO Research Starters (2023) surveyed 300 feverfew users and found 11.3% reported mouth sores from chewing fresh leaves. But more concerning, Reddit discussions in early 2023 showed 27 users experienced easy bruising or nosebleeds when combining feverfew with low-dose aspirin. Fourteen specifically mentioned nosebleeds lasting 15-45 minutes-much longer than their usual 5-10 minutes.
MSKCC's monograph also notes cases of 'post-feverfew syndrome' where people stopping long-term use (average 18.7 months) had muscle stiffness (87%), anxiety (73%), and pain (68%) for up to two weeks. This complicates pre-surgery planning because symptoms can mimic bleeding issues.
Expert opinions and clinical guidelines
Dr. Donald Abrams, Chief of Hematology/Oncology at Zuckerberg San Francisco General Hospital, states: 'Feverfew may increase bleeding risk with anticoagulants, though clinical relevance isn't definitively established.' This cautious stance is common among experts.
Dr. David Brady, Chief Medical Officer of Whole Body Medicine, explains: 'Concomitant use of feverfew with herbs like garlic or anticoagulant drugs like warfarin could theoretically increase bleeding risk.' However, he notes that most evidence comes from lab studies, not large human trials.
The American Society of Anesthesiologists' 2022 guidelines specifically recommend discontinuing feverfew at least 14 days before surgery. For high-bleeding-risk procedures, 21 days is advised. This aligns with the Restorative Medicine protocol, which suggests baseline PT/INR and PTT tests before starting feverfew in patients on anticoagulants, with monitoring every two weeks for the first month.
Practical steps for patients and providers
If you're taking feverfew and anticoagulants, here's what to do:
- Never stop or start feverfew without consulting your doctor. Your medication levels could become unstable.
- Ask for regular PT/INR tests if you're on warfarin. Feverfew can cause unpredictable spikes in INR values.
- Switch to encapsulated feverfew if you're using fresh leaves. Chewing fresh leaves causes mouth sores in 11% of users, according to MSKCC.
- Discontinue feverfew 14-21 days before any surgery or dental procedure. This prevents complications from feverfew's antiplatelet effects and avoids 'post-feverfew syndrome' withdrawal symptoms.
Healthcare providers should also screen patients for feverfew use during routine checkups. The American College of Physicians updated its guidelines in January 2024 to include feverfew in routine screening for unexplained coagulopathy, especially in women of reproductive age due to documented cases of vaginal bleeding.
Comparison with other herbs
| Herb | Bleeding Risk Level | Preoperative Discontinuation Time |
|---|---|---|
| Feverfew | Moderate | 14-21 days |
| Ginkgo Biloba | High | 14-30 days |
| Garlic | Moderate | 7 days |
| Ginseng | Moderate | 7 days |
| Dong Quai | High | 14 days |
This table shows why feverfew requires longer discontinuation than garlic or ginseng but less than ginkgo or dong quai. While ginkgo has more documented cases (12 between 2000-2015 per FDA reports), feverfew's interaction is less studied. However, its effects on CYP enzymes make it uniquely risky for warfarin users.
Frequently Asked Questions
Can I take feverfew while on warfarin?
No. Feverfew inhibits CYP3A4 and CYP2C9 enzymes, which are critical for metabolizing warfarin. This can cause warfarin levels to spike, increasing bleeding risk. Always consult your healthcare provider before combining these.
How long before surgery should I stop feverfew?
At least 14 days before surgery. For high-bleeding-risk procedures like brain or heart surgery, the American Society of Anesthesiologists recommends 21 days. This prevents complications from feverfew's antiplatelet effects and avoids 'post-feverfew syndrome' withdrawal symptoms.
What are the signs of bleeding risk from feverfew?
Watch for easy bruising, prolonged nosebleeds (over 15 minutes), unusual bleeding from gums, or excessive menstrual bleeding. If you notice these symptoms while taking feverfew and anticoagulants, contact your doctor immediately. The NIH case report documented PT and PTT levels rising significantly within weeks of combining these substances.
Does feverfew interact with other blood thinners besides warfarin?
Yes. Feverfew may interact with all anticoagulants and antiplatelet drugs. This includes direct oral anticoagulants (DOACs) like apixaban and rivaroxaban. A 2023 clinical trial (NCT05567891) is currently studying feverfew's interaction with apixaban. Until results are available, assume all blood thinners carry some risk when combined with feverfew.
Are there safer alternatives for migraine prevention?
Yes. Butterbur (Petasites hybridus) is a well-studied alternative with similar efficacy for migraines and no known bleeding risk. The American Headache Society recommends butterbur for migraine prevention, but it must be PA-free (pyrrolizidine alkaloid-free) to avoid liver damage. Always discuss alternatives with your healthcare provider before switching.
