Masseter Botox: What It Does to Your Jaw and Your Face

The masseter is one of the biggest muscles in the face. It’s the muscle you feel bulge at the angle of your jaw when you clench your teeth, and we inject it with Botox or another neuromodulator for two main reasons.

Reason 1: to slim a square or broad lower face

Injecting the masseter causes that muscle to atrophy, to shrink, and that changes the shape of the face. A square or broader face becomes more of a heart or an oval.

Who’s this for? Anyone with a bigger lower face, and especially women, where the bigonial width (the width across the angles of the jaw) is just as wide as the zygomatic width (the width across the cheekbones). That proportion isn’t felt to be as aesthetically pleasing as a face where the cheekbones are wider or more prominent than the lower jaw. Masseter Botox narrows the jaw so the cheekbones read as the widest point again.

Reason 2: clenching, grinding, and jaw pain

The other group is people who grind their teeth at night, rip through night guards, and have TMJ-type jaw pain. Weakening the masseter takes the force out of the clench. It reduces the grinding, it protects the teeth, it reduces the discomfort, and it can decrease some of the tension headaches that go along with clenching. Sometimes we also inject the temporalis muscle, at the side of the head, if a patient is getting discomfort in the temple area as well.

Plenty of people are in both groups at once. Plenty come for the pain and end up liking the slimming as a bonus.

One thing to say plainly: injecting the masseter for slimming or for grinding is off-label use of a neuromodulator in Canada and the US. It is also a relatively safe injection site with a long track record, so off-label here doesn’t mean experimental. It means the drug’s approved label doesn’t list this use, and your injector should be experienced with the muscle.

Units and how often

The masseter is injected at roughly the same interval as regular Botox, so every three to six months.

Rough starting units are anywhere from 15 to 30 units per side. Some people with quite strong masseters can need up to 60 units per side. The masseter typically uses more units than the forehead area, and neuromodulators are priced per unit, so it does cost more. Worth knowing before you compare quotes.

The timeline: relief is fast, slimming is slow

You’ll notice clenching or grinding relief as quickly as one to two weeks.

The slimming effect takes longer, and this is where people get impatient. Think of your masseter like your bicep: if you don’t use it, you lose it. That atrophy, the actual thinning of the muscle, takes time. You can see some slimming in four to eight weeks, but you’ll probably see the more maximal slimming after you’ve done three rounds of injections. That can mean six to twelve months to reach the maximal thinning.

So if you’re doing this for face shape, commit to a series, not a single appointment, and judge the result at the end of it.

Side effects, and who should think twice

Most people enjoy the effect of masseter Botox. But there are a few things I want you to know before you sit down.

If you’re thin, you may not like the atrophy. If you’re injecting purely because you grind, and you’re on the thinner side, you might not want your masseter to thin along with the relief. It will. Decide whether that trade is fine with you before you start.

If you’re older or already jowly, it can add a little jowling. In someone with a lot of sagging, the masseter is taking up some volume and helping to support the slackness of the lower-face skin. Weaken it and they may notice some increased jowling. It would be a small amount, but it could be enough to bother you, so keep it in mind if you’re particularly sagging or jowly.

Bulging, if it isn’t injected well. The masseter has different parts, superficial and deep, and some people have fibrous bands running through it. If the neuromodulator doesn’t diffuse well through the whole muscle, part of it stays strong and can bulge when you clench. This is easily corrected with a few more units.

Smile asymmetry, if it’s injected too far forward. An inexperienced injector who goes too anteriorly can hit the risorius, one of the smile muscles, and that affects the symmetry of your smile until it wears off.

Chewing fatigue. Some patients find they can’t chew as hard or as strong as they used to, because the muscle is weaker. This is usually short-lived and not bothersome to most people.

The bottom line

Masseter Botox does two things well: it takes the force out of a clench within a couple of weeks, and it slims a square jaw over a series of treatments across six to twelve months. It uses more units than most areas, so budget for that. And it’s not for everyone: if you’re very thin, or you’re already jowly, talk honestly with your injector about whether the trade is worth it for you.

Comparing your options? See our guide to masseter Botox, including cost ranges and clinics near you, and my article on Botox side effects for the general risks that apply anywhere on the face.