In the largest feverfew trial, adverse events were lower on the herb than on placebo, at 8.4% against 10.2%. Those 2 figures come before any caution list.
They were 8.4% on feverfew and 10.2% on placebo. The real cautions here are about who should avoid it rather than what it does.
Quick Answer: What Are the Side Effects of Feverfew?
Mild, in the trial data. Adverse events possibly related to treatment occurred in 8.4% of the feverfew group against 10.2% on placebo, a difference that was not significant. Mouth ulceration is the classic reported effect, particularly with chewed fresh leaves. The cautions that matter are pregnancy, anticoagulants, and daisy-family allergy.
Key Takeaways
- Adverse events were 8.4% on feverfew against 10.2% on placebo.
- That difference was not statistically significant, at p equals 0.654.
- Mouth ulceration is the classic effect, mostly from 1 habit: chewing leaves.
- Avoid in pregnancy, and ask first about any 1 of the anticoagulants.
- The daisy-family list covers 4: ragweed, chrysanthemums, marigolds and daisies.
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What the Trial Recorded
Starting with the measured data rather than a warning list gives a fairer picture.
| Measure | Feverfew extract | Placebo |
|---|---|---|
| Adverse events possibly related | 9 of 107 | 11 of 108 |
| As a percentage | 8.4% | 10.2% |
| Statistical difference | p equals 0.654 | Not significant |
| Duration | 16 weeks | 16 weeks |
| Also monitored | Laboratory parameters, vital signs, examination | Same |
A supplement producing fewer reported events than placebo is a genuinely reassuring result.[1]Efficacy and safety of 6.25 mg t.i.d. feverfew CO2-extract (MIG-99) in migraine prevention - a randomized, double-blind, multicentre, placebo-controlled study — Cephalalgia (2005) View source What the herb is comes first, in the main feverfew guide.
The Classic Reported Effect
Mouth ulceration is the one associated with feverfew historically, and the context matters.
- Most associated with: Chewing fresh leaves.
- Also reported: Mouth soreness and swelling.
- Less common with: Capsules and extracts.
- Other reports: Digestive upset and bloating.
That is 1 reason capsules replaced leaf-chewing as the usual form, and it is also why the reported effect rate differs so much between the 2 traditions.
Who Should Avoid It
Four groups, and the last one is the least obvious.
| Group | Why |
|---|---|
| Pregnancy or planning pregnancy | Traditional emmenagogue use; avoid |
| On anticoagulants or antiplatelets | Bleeding-risk concern; ask first |
| Before surgery | Same concern; stop in advance and tell the team |
| Daisy-family allergy | Ragweed, chrysanthemums, marigolds, daisies |
| Children | Not studied at supplement doses |
The plant-family point catches people out because feverfew looks like a daisy and is one, which is exactly the confusion covered in is feverfew the same as chamomile.
Stopping It
A withdrawal pattern has been described in long-term users, and it is worth planning around.
- Reported on stopping: Rebound headache and muscle stiffness.
- Mostly in: People who took it for long periods.
- Practical step: Taper rather than stopping abruptly.
- Trial evidence: The 16-week trials did not measure this.
That last line matters: the withdrawal pattern comes from clinical description rather than from the randomized trials, so treat it as a sensible precaution rather than a measured effect.
Interactions
The live search questions here are almost all about medication, and the honest list is short.
| Category | Position |
|---|---|
| Anticoagulants and antiplatelets | The main concern; ask before starting |
| Migraine prescriptions | No established interaction; still worth mentioning |
| Anti-inflammatories | No established interaction |
| Other herbs affecting bleeding | Caution when stacking several |
| Alcohol | No established interaction |
Amounts and forms are compared in the dose and form guide, and the interaction question matters more than the number.
The whole evidence base is 6 trials in 561 patients, which limits confidence about rare harms as much as about benefits.[2]Feverfew for preventing migraine — Cochrane Database of Systematic Reviews (2015) View source
- Reassuring: 8.4% adverse events against 10.2% on placebo.
- Limiting: Only 6 trials, in 561 patients.
- Unstudied: Use beyond 16 weeks.
A 2025 pooling of 9 trials in 899 participants reached the same modest conclusion.[3]Systematic review and meta-analysis of Tanacetum parthenium: evaluating its efficacy in migraine relief — Natural Product Research (2025) View source For everyone outside those groups, the capsule we sell has an undramatic record.
Seek Urgent Assessment Rather Than Continuing If
- A sudden severe headache unlike any before, or a headache with fever, neck stiffness, confusion, weakness, vision loss or after a head injury
- Any change in the pattern, frequency or character of long-standing migraines
- Pregnancy, or planning a pregnancy
- Taking warfarin, another anticoagulant, or an antiplatelet medicine
- A known allergy to ragweed, chrysanthemums, marigolds or daisies
Frequently Asked Questions
What are the risks of taking feverfew? +
In the largest trial, adverse events were 8.4% against 10.2% on placebo. The main risks are situational: pregnancy, anticoagulants and daisy-family allergy.
Who should not take feverfew? +
Anyone pregnant, anyone on anticoagulants, anyone due for surgery, and anyone allergic to ragweed or daisies. That is 4 groups.
Who should avoid feverfew? +
The same 4 groups, plus children, since feverfew has not been studied in them at supplement doses.
What not to take with feverfew? +
Anticoagulant and antiplatelet medicines without asking first. That is the 1 category with a genuine concern behind it.
What medications should not be taken with feverfew? +
Warfarin and other blood-thinning medicines are the ones to raise with a pharmacist. There are 0 established interactions with common migraine prescriptions.
Is it safe to take feverfew daily? +
Daily use for 16 weeks was well tolerated in the trial, with fewer adverse events than placebo. Longer-term use has not been studied in the same way.
Is feverfew safe for the liver? +
Liver problems are not among the reported effects, and laboratory parameters were monitored in the 16-week trial. Butterbur is the herb with the liver concern.
Does feverfew affect blood pressure? +
Vital signs were monitored in the trial and no blood pressure signal was reported. There are 0 trials of feverfew for blood pressure.
Does feverfew cause mouth ulcers? +
It is the classic reported effect, associated mainly with 1 habit, chewing fresh leaves, rather than with capsules.
Can I stop taking it suddenly? +
A rebound pattern of headache and stiffness has been described in long-term users. Tapering over 1 or 2 weeks is the sensible approach.
Does feverfew affect serotonin? +
There are 0 human trials measuring that. The mechanism proposed for migraine involves inflammatory pathways rather than serotonin levels.
Is it safe in pregnancy? +
No. Feverfew should be avoided in pregnancy and by anyone planning 1.
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