Dear Editor, OnabotulinumtoxinA (BOTOX) has been approved for prophylaxis in chronic migraine (CM) since 20101 based on the findings of the Phase 3 REsearch Evaluating Migraine Prophylaxis Therapy (PREEMPT) trial.2 The duration of BOTOX efficacy is known to be 3 months, but prolonged efficacy (>3 months) after a single cycle of BOTOX has not been evaluated thoroughly. Moreover, the efficacy and...
