What is butterbur?

Butterbur (Petasites hybridus) is an herb most commonly known for its use in migraine prevention, although it is falling out of favor due to the risk of liver toxicity.^[1] Its name comes from its large hat-like leaves which historically were used to wrap butter to protect it from the weather. Butterbur typically grows in North America, Asia, and Europe within wet marsh areas or close to rivers or streams.^[2]