View photos of the medicinal plant Clematis drummondii (Virgin’s bower), profiled in Medicinal Plants of the American Southwest.

A passage from Medicinal Plants of the American Southwest:

Applied as a preventative, use Clematis to abort a migraine when visual and auditory disturbances are first noticed, before the intense pain of an episode fully develops. If a strong cup of Coffee (or Periwinkle) has no effect on the migraine (or makes it worse) try Clematis.