Matharu M, Pascual J, Nisson Remahl I, Straube A, Lum A, Davar G, Odom D, Bennett L, Proctor C, Gutierrez L, Andrews E, Johannes C. Utilization and safety of onabotulinumtoxinA for the prophylactic treatment of chronic migraine from an observational study in Europe. Cephalalgia. 2017 Dec;37(14):1384-97. doi: 10.1177/0333102417724150