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OnabotulinumtoxinA 72 U reduces masseter prominence versus placebo in adultsDoes this shot really shrink a prominent jaw muscle, or is it just a placebo effect?

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Key Takeaway
Consider onabotulinumtoxinA 72 U for masseter reduction, noting the significant trial results and favorable safety profile.

This was a Phase 3, randomized, placebo-controlled, multiregional trial in 376 adults with Grade 4 or 5 masseter muscle prominence (MMP) on the investigator-assessed MMP Scale. The study was a prospective, multicenter trial with a 6.0-month follow-up period.

Participants received either onabotulinumtoxinA 72 U or a placebo comparator. The primary outcome was a ≥2-grade improvement from baseline on the investigator-assessed MMPS.

The main results showed that 51.2% of participants in the onabotulinumtoxinA group achieved the primary outcome, compared to 2.2% in the placebo group (P < .0001). For lower-facial width reduction, the mean change was -5.24 mm with onabotulinumtoxinA versus -0.04 mm with placebo (P < .0001).

Safety data indicated that most adverse events were mild, nonserious, and resolved. The trial reported a favorable safety profile. Key limitations include the lack of reported funding or conflicts, and the absence of reported practice relevance or causality notes.

These results suggest a potential benefit for onabotulinumtoxinA in reducing masseter prominence, but the findings are specific to the trial population and follow-up duration.

Imagine looking in the mirror and seeing a jaw muscle that feels too big or looks too high. For many adults, this condition causes real distress. A new study looked at whether a specific injection could help shrink this muscle. The research involved 376 adults who had severe muscle prominence, rated as Grade 4 or 5 on a standard scale. They received either the active treatment or a placebo, which is an inactive sugar pill used to test if the real drug works better than nothing.

The results were striking. Over half of the people who got the active treatment saw a major improvement in their muscle appearance. In contrast, only a tiny fraction of those on the placebo saw such a change. The treatment also led to a measurable narrowing of the lower face. These changes happened quickly and lasted for six months, the time the study followed participants.

Safety was a key concern for everyone involved. Most side effects were mild, not serious, and went away on their own. No one had to stop the treatment because of severe problems. However, this is one study. While the numbers look promising, we need more research to be absolutely sure this works for everyone and to understand long-term effects.

What this means for you:
This treatment significantly reduced jaw muscle size in severe cases, with few side effects reported.

Study Details

Study typeRct
Sample sizen = 283
EvidenceLevel 2
Follow-up6.0 mo
PublishedApr 2026
View Original Abstract ↓
BACKGROUND: Masseter muscle prominence (MMP) may be aesthetically bothersome to some individuals, leading them to seek treatment for a slimmer lower face. OBJECTIVES: The aim of this study was to evaluate the safety and efficacy of onabotulinumtoxinA for the treatment of MMP, including patient-reported outcomes (PROs). METHODS: This was a prospective, multicenter trial including a randomized, double-blind, placebo-controlled period (Days 1-180) in which adults rated Grade 4 or 5 (marked/very marked) on the investigator-assessed MMP Scale (MMPS) were randomized to onabotulinumtoxinA 72 U or placebo. Efficacy endpoints were assessed at Day 90. The primary endpoint was ≥2-grade improvement from baseline on the investigator-assessed MMPS. Secondary endpoints included achieving Grade ≤3 on the MMPS and participant-assessed MMPS-Participant (MMPS-P), ≥2-grade improvement on the participant-assessed MMPS-P, and change from baseline in lower-facial width. Outcomes were assessed using validated measures. Adverse events (AEs) were monitored. RESULTS: Of 376 enrolled participants (onabotulinumtoxinA, n = 283; placebo, n = 93), 310 (82.4%) completed the study. At Day 90, a greater proportion of onabotulinumtoxinA-treated participants vs placebo achieved MMPS ≥2-grade improvement (51.2% vs 2.2%, P < .0001), and more onabotulinumtoxinA-treated participants vs placebo achieved the secondary endpoints (all P < .0001), with a mean lower-facial width reduction of -5.24 mm for onabotulinumtoxinA vs -0.04 mm for placebo (P < .0001). Participants reported benefits for onabotulinumtoxinA vs placebo in self-perceived change in MMP, treatment satisfaction, and psychosocial impact. Improvements were sustained through Day 180. Most AEs were mild, nonserious, and resolved. CONCLUSIONS: OnabotulinumtoxinA effectively reduced the appearance of MMP and improved PROs, with effects lasting up to 6 months and a favorable safety profile.
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