Masseter Botox for jaw slimming: what the label and the studies say

Botox injected into the masseter, the main chewing muscle at the angle of the jaw, is used to slim the lower face. It isn't a use on any cosmetic botulinum toxin label.¹

This page covers what the label says, what the best studies we found say, and what to ask. It gives no dose and no injection plan. Whether to have it is for you and a clinician.

What it is

The masseter is the muscle that closes the jaw. Masseter muscle hypertrophy, an enlarged muscle, is a benign condition that can alter the contour of the lower face.² The plastic surgeons' society lists thick jaw muscles among the areas treated with botulinum toxin, and softening a square jawline among the things it can do.⁵

What the label says

The Botox Cosmetic label lists four uses in adults: frown lines, lateral canthal lines (crow's feet), forehead lines and platysma bands in the neck.¹ The masseter isn't among them, and the labels of the four other cosmetic brands don't list it either. Using Botox there is an off-label use. Doctors may use approved drugs this way, but the label doesn't describe the use, so ask what your provider's plan is based on.

What the studies say

A 2026 systematic review and meta-analysis pooled five randomized trials with a placebo group, 536 people in all. Botulinum toxin was linked to better masseter prominence, thinner muscle and higher satisfaction than placebo. It appears to give short-term improvement, the authors write.²

The same review is cautious. Results varied a great deal between trials, so the size of the change in muscle thickness should be read with care. The evidence is not enough to say what the best treatment plan is, and it calls for longer, standardized trials.² A 2022 review of 28 studies found the same problem: mixed results, a high level of bias and selective reporting made it hard to compare how treatment is done.⁴

Biting strength

The masseter does the biting, so weakening it can reduce bite force. In a small non-randomized trial of 20 people treated and 12 untreated, maximal bite force was significantly reduced at 3 months and no longer significantly reduced at 6 months. The authors say the reduction was reversible, and that the visible change may last longer.³

Risks

Every botulinum toxin label carries a boxed warning. The effects can spread from the injection site and cause symptoms such as weakness, double vision, trouble swallowing and trouble breathing, hours to weeks after injection. Swallowing and breathing difficulties can be life threatening.¹

Ask your provider what the risks specific to the jaw are.

What this page doesn't cover

We don't cover Botox for teeth grinding or jaw pain.

Which licensed professionals may inject depends on your state. See our guide to choosing a Botox provider and our comparison of the five brands.

Cost

We don't give prices on this page. Our Botox cost guide covers how clinics quote, which is per unit for other areas.

Common questions