Long-Term Efficacy of Botulinum Toxin Type A: A 10-Year Cohort

Background: The long-term efficacy and safety profile of repeated onabotulinumtoxinA injections for glabellar rhytids remains incompletely characterized, with most published data limited to 24 months of follow-up. Objective: To evaluate cumulative treatment response, duration of effect, receptor desensitization, and safety of onabotulinumtoxinA in the glabellar complex over a 10-year period. Methods: Prospective, multicenter cohort of 1,284 adult patients (mean age 46.2 years; 87% female) receiving standardized 20-unit glabellar injections every 3 to 6 months from 2014 through 2024. Wrinkle severity was assessed with the validated Facial Wrinkle Scale at baseline and at each visit. Neutralizing antibody titers were measured at years 2, 5, and 10 in a subgroup of 312 patients. Results: Mean duration of clinically meaningful effect increased from 3.4 months after the first cycle to 4.1 months by year 5 and remained stable thereafter. At 10 years, 91.3% of patients maintained at least a 1-point improvement on the Facial Wrinkle Scale at 4 months post-injection. Neutralizing antibodies were detected in 0.6% of tested patients, none of whom demonstrated clinical secondary non-response. Adverse events were transient and dose-related; no cases of permanent muscle atrophy or systemic toxicity were reported. Conclusions: Repeated onabotulinumtoxinA injection over a decade produces durable, reproducible glabellar smoothing without cumulative desensitization or new safety signals, supporting long-term use in appropriately selected patients.