Blumenfeld AM, et al. - Researchers here sought to perform a long-term study of the efficacy and safety of OnabotulinumtoxinA for the prevention of chronic migraine (CM). In this work, clinical evidence supporting the consistency of the efficacy and the long-term safety and tolerability of onabotulinumtoxinA was gained for the prevention of headache in those with CM who have been treated with onabotulinumtoxinA every 12 weeks over 2 years (9 treatments) with the fixed-site, fixed-dose injection paradigm.