The Petasites hybridus root, or butterbur, is a shrub native to Europe (as well as some parts of North America and Asia) that has traditionally targeted ailments including migraine and fever for centuries, according to the National Institutes of Health. But more recent research also backs the historic use of this plant in treating migraines. A 2006 review of 293 patients by a Swiss research and headache diagnosis center showed higher doses of the Petasites root extract Petadolex reduced the occurrence of headaches over a roughly four month period. Last year, both the Canadian Headache Society and a committee of the American Headache Society issued papers recommending its use for migraines. But a word of caution: there is not enough research to back the safety of its long-term use, and the NIH says that the plant in its unprocessed forms contains chemicals that may harm the liver. Consumers should be careful to look for forms of butterbur that have been processed to remove these chemicals, called pyrrolizidine alkaloids.