A Study To Assess the Safety of OnabotulinumtoxinA (BOTOX) Intramuscular Injection in Adult Participants With Platysma Prominence

This is a Phase 3, open-label extension study to evaluate the long-term safety of repeat BOTOX treatments in adult participants with Platysma Prominence. Participants who completed the lead-in Phase 3 Study M21-309 and met eligibility requirements could enroll in this open-label extension study. Planned study enrollment was approximately 270 participants. Participants who met treatment criteria could receive up to 3 administrations of BOTOX. Day 1 (study entry) was the same day as Day 120/study exit visit of the lead-in Phase 3 study. The first administration of study drug could occur at the Day 1 visit, and the last administration of study drug could occur at the Day 180 visit (60 days prior to Day 240/study exit). Once a subject was enrolled in this study, monthly follow-up visits occurred.