OBJECTIVE: Migraine is still an unsolved problem. This clinical trial investigates the efficacy and tolerance of Petasites hydridus in the prophylaxis of migraine. METHODS: A randomized, group-parallel, placebo-controlled, double-blind clinical study was carried out with a special CO2 extract from the rhizome of Petasites hybridus. Following a 4-week run-in phase, 60 patients received either the special Petasites hybridus extract petadolex or placebo at a dosage of 2 capsules (each capsule contains 25 mg) twice daily over 12 weeks. Outcome variables included the frequency, intensity and duration of migraine attacks as well as any accompanying symptoms. RESULTS: The frequency of migraine attacks decreased by a maximum of 60% compared to the baseline. This reduction in migraine attacks with petadolex was significant (p < 0.05) compared to placebo. No adverse events were reported. Petasites was exceptionally well tolerated. CONCLUSIONS: The results suggest that migraine patients can benefit from prophylactic treatment with this special extract. The combination of high efficacy and excellent tolerance emphasizes the particular value that Petasites hydridus has for the prophylactic treatment of migraine. Grossmann M, Schmidramsl H. Int J Clin Pharmacol Ther 2000 Sep;38(9):430-5.