How does butterbur work?

There are a few different proposed mechanisms for how butterbur helps to prevent migraine. First, the butterbur constituents petasin and isopetasin have been shown to reduce the constriction of blood vessels and decrease neuron excitation by inhibiting L-type voltage-gated calcium channels (which relax the smooth muscles that control the diameter of blood vessels). Additionally, independent of petasin content, butterbur extract has been shown to inhibit COX-2 enzymes, which produce inflammation-causing prostaglandins. Finally, some research suggests that butterbur root extract reduces the sensation of pain by acting on two types of ion channels that are also triggered by spicy food (TRPA1 and TRPV1).^[1][2]