here's the basis on what was said in that article about pharmaceutical or the safety of butterbur products:

Butterbur root should never be consumed directly from the plant, since it contains compounds called pyrrolizidine alkaloids that have may have hepatotoxic and carcinogenic effects.17

However, extracts that are prepared for human use are processed to remove these alkaloids. An independent evaluation of data gathered from various trials concluded that commercially marketed butterbur root extract is entirely safe for human consumption.26 A standardized butterbur extract has been used by more than half a million German citizens since its introduction in 1988, and the safety data are excellent.18

A dosage of 50-75 mg of standardized butterbur extract twice daily for up to four months has demonstrated efficacy in migraine prevention,17 while 50 mg twice daily has been used in the management of allergic rhinitis.17

No instances of overdose with butterbur have been reported in the scientific literature,17 but anyone who has a known allergy to plants in the Asteraceae family, such as ragweed or daisies, should consume butterbur with caution.