The reports on feverfew prompted a controlled, double-blind clinical trial conducted at the City of London Migraine Clinic, using patients who reported being helped by the herb. Those who received the placebo, and therefore stopped using feverfew, had a significant increase in the frequency and severity of headache, nausea and vomiting during the six month study, while patients taking feverfew showed no change in the frequency or severity of their symptoms. Two patients in the placebo group who had been in complete remission during self-treatment with feverfew leaves started having incapacitating migraine again, and had to withdraw from the study. Once they resumed self-treatment, their symptoms once again disappeared.In another trial undertaken at Nottingham University Hospital, the patients who took feverfew had 25 per cent fewer migraine attacks and suffered less nausea and vomiting during attacks.

According to Dr Stewart Johnson (formerly of the City of London Migraine Clinic) who pioneered research into using feverfew to treat migraine, scientific tests have shown that feverfew is a safe substance to take, even over a long period of time. However, as with all medicines, pregnant and lactating women should consult their doctor before taking it.