Nobre, Bryanne Brissian de SouzaRezende, LucianaCâmara-Souza, Mariana BarbosaSanchez-Ayala, AlfonsoBlass, RodrigoCarbone, Ana ClaudiaManso, Ana CristinaErnberg, MalinChristidis, NikolaosCanales, Giancarlo De la Torre2026-03-312026-03-312024-06de Souza Nobre, B.B., Rezende, L., Barbosa Câmara-Souza, M. et al. Exploring botulinum toxin’s impact on masseter hypertrophy: a randomized, triple-blinded clinical trial. Sci Rep 14, 14522 (2024). https://doi.org/10.1038/s41598-024-65395-52045-2322http://hdl.handle.net/10400.26/62551The present study aimed to assess the effectiveness and functional adverse effects of a single and multiple injections of botulinum toxin A (BoNT-A) for masseter hypertrophy (MH). Twenty-six women complaining about lower third facial enlargement due to MH, received 75 U of BoNT-A (abobotulinum toxin) in each masseter muscles. After 3 months, patients were randomly assigned to receive a second treatment session of Saline Solution: (G1; n = 11) or BoNT-A: (G2; n = 12). Muscle thickness (ultrasound), electrical activity (electromyography; EMG), masticatory performance, and subjective perception of MH were evaluated. Follow-up was performed at 1, 3 and 6 months. Muscle thickness, EMG activity, and masticatory performance were analyzed using ANOVA two-way and Sidak test as post-hoc. Masticatory performance was analyzed by the Friedman’s test and Mann–Whitney test. Regarding inter-groups comparisons, there was a significant decrease in the left masseter muscle thickness in the G2 group at the 6 month follow-up (p < 0.02). For EMG, significant differences were evident at the 6 month assessment, with higher masseter activity for G1 (p < 0.05). For masticatory performance, no significant differences were observed throughout the study (p > 0.05) and a higher improvement in subjective perception of MH was observed in the 1 month follow-up for G2 (p < 0.05). In conclusion, BoNT-A is effective for MH, however multiple injections cause functional adverse effects in masseter muscle.engBotulinum toxin type AMasseter hypertrophyMuscle thicknessMasticatory performancecontribution to journal10.1038/s41598-024-65395-5