The Common Butterbur (Petasites hybridus) – Portrait of a Medicinal Herb For hundreds of years butterbur (Petasites hybridus;) has been used against many diseases. Modern indications are the prophylaxis of migraine, tension headache, spasms of the urogenital tract, gastro-intestinal tract and bile duct and hopefully hay fever and asthma in the near future. The petasines, the main components of butterbur, inhibit the synthesis of leucotrienes and decrease the intracellular concentration of calcium which explains the anti-inflammatory and spasmolytic properties of extracts of butterbur. Thanks to extraction with supercritical CO₂ the concentrations of the potentially hepatotoxic and carcinogenic pyrrolizidine alkaloids lie below the detection limits. Until now four cases of a reversible cholestatic hepatitis have been probably associated with long-term administration of butterbur (incidence of 1:175.000). It is unknown which components of butterbur are responsible for the long-term hepatotoxicity. Further side effects involve the gastrointestinal tract and are usually mild.