Butterbur (Petasites hybridus) has been studied for its potential in preventing migraines. Clinical trials, especially those conducted in the early 2000s, indicated that standardized extracts of butterbur root (specifically Petadolex®) may reduce migraine frequency in adults and children. Two well-designed randomized, placebo-controlled trials published in Neurology (2004) and Headache (2005) found that 75 mg twice daily significantly reduced migraine attack frequency compared to placebo. Based on these and other studies, organizations such as the American Academy of Neurology (AAN) and the American Headache Society (AHS) previously endorsed butterbur as “probably effective” for migraine prevention.

However, concerns have been raised about the safety of butterbur due to the presence of hepatotoxic pyrrolizidine alkaloids (PAs) in unprocessed extracts, which can cause liver damage. Only PA-free and standardized extracts should be used, though long-term safety data are limited. Recent guidelines have downgraded recommendations for butterbur because of these safety concerns.

In summary, there is moderate quality scientific evidence supporting butterbur's efficacy for migraine prevention, but safety concerns about liver toxicity have limited its clinical use and recommendation. Its use should be considered with caution and only under guidance with guaranteed PA-free extracts.