Botulinum neurotoxin A for chronic migraine headaches: does it work and how?

In 2010, botulinum neurotoxin A (BoNTA) was approved to prevent headaches in adult patients with chronic migraine. The approval was based on the outcomes of two multicenter clinical trials (PREEMPT 1 & 2) that tested the efficacy and safety of BoNTA [1,2]. In PREEMPT 1, the primary efficacy end point, which was the average number of headache episodes, was similar for BoNTA and placebo. However, the number of headache days was reduced in the BoNTA group [1]. In the PREEMPT 2, the primary efficacy end point was the mean change from baseline in headache days from 21–24 weeks post-treatment and...