Some migraineurs recommend butterbur as a migraine preventative, so I researched it.

“Depending on how they are prepared, butterbur remedies may contain chemicals called pyrrolizidine alkaloids (PAs). These are known to damage the liver and can cause serious illness. It is only safe to take butterbur products that are certified as ‘PA-free,’ as these products have been processed in a way that removes the dangerous chemicals.”

Researchers in Germany found butterbur to be “effective in reducing the number of days with migraines per month, in decreasing migraine-associated symptoms, and in reducing both the duration and intensity of migraine pain. Petasites extract [i.e., butterbur] has a history of excellent tolerance, and no adverse side effects have been reported.” Another practice is to use a combination of butterbur and feverfew for even greater effectiveness.

References

Burgess, Lana; medically reviewed by Debra Rose Wilson, PhD, MSN, RN, IBCLC, AHN-BC. “What are the health benefits of butterbur?” Medical News Today (October 11, 2017). https://www.medicalnewstoday.com/articles/319667.php (accessed on 8/3/2020).
What are the health benefits of butterbur?
Depending on how they are prepared, butterbur remedies may contain chemicals called pyrrolizidine alkaloids (PAs). These are known to damage the liver and can cause serious illness. It is only safe to take butterbur products that are certified as “PA-free,” as these products have been processed in a way that removes the dangerous chemicals.

English, Jim. “Butterbur Extract (Petasites Hybridus) Effective in Reducing Migraine Attacks,” Nutrition Review (April 19, 2013). https://nutritionreview.org/2013/04/butterbur-extract-petasites-hybridus-effective-reducing-migraine-attacks/ (accessed on 8/3/2020).

Meschino, James P., DC, MS. “Natural Supplements for Migraine Prevention: Butterbur and Feverfew,” Dynamic Chiropractic (September 9, 2010, Vol. 28, Issue 19). https://www.dynamicchiropractic.com/mpacms/dc/article.php?id=54885 (accessed on 8/3/2020).