alerted by Metafilter to a wonderful information rich graphic sorting the evidence for the efficacy of various dietary supplements. The graph is entitled Snake Oil Supplements, not least because it is distinctly bottom-heavy. There is loads of products [see R] below the possibly useful line, outnumbering the things which have a chance of doing something useful. As Dara O'Briain says, "the parts of herbal medicine that work have become medicine and the rest is a nice bowl of soup and some pot pourri".
Cochrane Index, appears to reduce the number of migraine attacks by 0.6 per month. According to this (not massive) controlled study, if you consume this herb, you'll have 6 fewer migraine in a year. That sound like a lot and we have stands of the stuff growing in our polytunnel at the other end from the poppies. The French call it Pyrèthre doré but the Germans say fieberkraut like the Anglophones. Spanish has a whole clatter of different common names including hierba santa. The Cochrane Index is the GoTo place for evidence for the safety and efficacy of drugs, treatments and medical practice. If The Index gives something even a qualified Yes, you should pay attention. Seems that a suitable dose regime is 2 or 3 feverfew leaves every day as a prophylactic against migraine. If you want to take a bit for arthritis, fevers, muscle tension, lower blood pressure, stomach irritation, to improve kidney function, colitis, dizziness, tinnitus or menstrual problems, you work away but there is NO evidence of efficacy against those conditions. You'll probably get similar benefit making a tisane from the packaging in which your feverfew tea-bags are sold.