Butterbur (Petasites hybridus) is an herb primarily used for migraine prevention, though its popularity is declining due to potential liver toxicity. It is named for its large leaves, which were historically used to wrap butter, and it typically grows in wet marsh areas or near rivers in North America, Asia, and Europe.

Butterbur is primarily known for preventing migraines, although its recommendation has been retracted due to safety concerns. It has also been used for allergic rhinitis and showed some effectiveness in reducing symptoms, but further research is needed to confirm its efficacy in asthma and compare it to other antihistamines.

Butterbur can cause common side effects such as burping, stomach upset, and headaches, as well as allergic reactions like itchy eyes and wheezing, particularly in people who are allergic to ragweed and daisies. Additionally, it contains toxic pyrrolizidine alkaloids, which have been linked to rare cases of liver toxicity.

Butterbur works to prevent migraines by reducing blood vessel constriction and neuron excitation through the inhibition of L-type voltage-gated calcium channels, as well as by inhibiting COX-2 enzymes that produce inflammatory prostaglandins. Additionally, it may alleviate pain by acting on specific ion channels associated with pain sensation.