The causes of migraine aren't well understood. Neither is the mechanism behind feverfew's proven ability to stop or prevent a migraine headache. Feverfew supplements used in clinical studies to treat migraine contain a standardized dose of 0.2 to 0.35% parthenolide, so if you research this herb, pay attention to dosage details. Pregnant women and children under the age of two shouldn't use it, and people with allergies to ragweed, chamomile and yarrow are sometimes allergic to feverfew. (