Efficacy of botulinum toxin for masseter muscle hypertrophy: A systematic review and meta-analysis.

Abstract

Masseter muscle hypertrophy (MMH) is a benign condition that can alter lower facial contour and cause esthetic concern. Botulinum toxin type A (BoNTA) is widely used as a minimally invasive treatment; however, the magnitude and consistency of its benefit remain uncertain. We performed a systematic review and meta-analysis of randomized, placebo-controlled trials evaluating BoNTA for MMH treatment. The Cochrane CENTRAL, Embase, and PubMed databases were searched. The primary outcome was change in masseter muscle thickness (MMT) during maximal clenching. Secondary outcomes included achieving a Masseter Muscle Prominence/Hypertrophy Scale (MMPS/MMHS) score of ≤3 and patient satisfaction. Random-effects models were used to pool data. Five randomized controlled trials involving 536 participants were included. BoNTA was associated with improved masseter prominence outcomes compared with placebo across multiple follow-up time points. At week 4, the pooled relative risk for achieving an MMPS/MMHS ≤3 was 5.25 (95% CI, 1.88-14.66) for 48 U and 3.66 (95% CI, 1.29-10.34) for 72 U. BoNTA was also consistently associated with reduced MMT and higher patient satisfaction. However, heterogeneity was substantial, indicating that the exact magnitude of MMT reduction should be interpreted cautiously. BoNTA appears to provide short-term improvement in masseter prominence, muscle thickness, and patient-reported outcomes in MMH compared with placebo. Nominal 48 U and 72 U regimens were associated with benefit, but current evidence is insufficient to define a formulation-adjusted dose-response relationship or an optimal treatment protocol. Further standardized randomized trials with longer follow-up are needed.