* Feverfew. This herb (Tanacetum parthenium) is probably the most effective plant for preventing migraine. Trials show that remedies standardised to around 250 mcg of parthenolide can reduce the severity, duration and frequency of migraines (Phytother Res, 1997; 11: 508-11). When using feverfew, be patient - it can take four to six weeks before results become evident.

* Cayenne pepper. According to the Natural Health Education Institute (NHEI) at Bastyr University, there is evidence to suggest that this widely grown peppery herb has migraine-preventing potential. Cayenne can make nerve endings less sensitive to painful stimuli by its effect upon substance P (a neurotransmitter for pain, touch and temperature) in the nervous system.

* Ginkgo biloba. This herb can strengthen the vascular system. There is also some evidence to suggest that Ginkgo can inhibit the action of what is known as ‘platelet-activating factor’, which is believed to contribute to migraine headaches. Unfortunately, there are no trials to confirm this.

* Butterbur. Taking 50 mg of a standardised extract of butterbur (Petasites hybridus) twice daily was shown in a double-blind trial to reduce the incidence of migraine attacks for up to three months (Freie Arzt, 1996; May/ June: 3). The downside is that butterbur contains pyrrolizidine alkaloids (PAs), substances that are potentially harmful to the liver, so its use should be supervised by a qualified practitioner.