When taken at the onset of a migraine headache, higher amounts of feverfew are often used. However, the optimum dosage has not been determined. Among the many thousands of people who use feverfew as a folk medicine in England, no reports of serious toxicity have been published. A smaller percentage reported mild gastrointestinal distress. However, mouth sores do not seem to occur in people who use encapsulated feverfew.
Animal studies confirm the safety of feverfew.
No adverse effects were seen at doses 100 and 150 times the human daily dose in rats and guinea pigs respectively. However, because feverfew was an old folk remedy used to promote abortions, it should probably not be taken during pregnancy. Safety in young children and those with severe liver or kidney disease has also not been established. May Help Prevent Migraines Magnesium is another natural treatment that appears to be effective for the prevention of migraine headaches. Similar results have been seen in other double-blind studies.