Does it work?

Butterbur (Petasites hybridus) is a perennial shrub, found throughout Europe as well as parts of Asia and North America. Pain relief and headache prevention are traditional uses of butterbur. Recent pre-clinical studies suggest anti-inflammatory and vasodilitary (blood vessel opening) properties of butterbur, thereby supporting a possible mechanism of action. A small number of human trials report efficacy of butterbur for migraine prevention when taken regularly for up to four months. This evidence is compelling enough to suggest benefits of butterbur for migraine prophylaxis, although additional evidence from larger, well-designed studies is necessary.

Dangers and possible side effects.....

The use of butterbur during pregnancy and lactation should be avoided due to a lack of safety studies. Butterbur should not be used if there is an allergy to plants in the Aster family, including ragweed, marigolds, daisies, and chrysanthemums.