Masseter (jaw) botulinum toxin
Masseter treatment delivers 20–30 units per side into the thick body of the chewing muscle to reduce its strength and, over time, its volume.
- Procedure time
- 10–15 minutes
- Anaesthesia
- Usually not needed; topical anaesthetic cream on request
- Recovery
- Back to normal the same day
- Sessions
- One session · assessed at weeks 4–6
- How long it lasts
- 6–9 months
The target muscle: masseter
Masseter runs from the cheekbone to the angle of the jaw and closes the mouth. Relative to its mass it is one of the strongest muscles in the body, and it works all day — talking, chewing, and clenching under stress.
A muscle that is constantly overworked thickens. A thickened masseter widens the lower face and makes the jaw angle prominent; the same patient often wakes with a sense of fatigue in the jaw and temples.
The target is the thick body in the lower and posterior part of the muscle. You are asked to clench, the bulge is bounded by hand, and the injections stay inside that safe zone.
How the dose is calculated
The typical range for masseter is 20–30 units per side, which usually comes to 40–60 units for both. This is the highest-dose non-expression area in the face.
The exact dose is set at examination. The thickness of the muscle is assessed by hand while you clench; where the sides differ, the doses are set separately.
- Muscle thickness — the size of the bulge when the teeth are clenched
- How severe and how long-standing the clenching habit is
- Asymmetry between sides — the thicker side gets the higher dose
- Response to previous treatments — the muscle thins with repetition, so the dose can come down
- The goal — if only muscle pain is being addressed, the dose can be lower than for a change in volume
The day of treatment
The jaw angle is marked and injections are given at 3–4 points per side. Total time is 10–15 minutes and most patients need no anaesthetic.
The needle goes deeper here than in the expression areas, into the body of the muscle. What you feel is short-lived pressure and tightness.
For the first day, avoid food that needs hard, prolonged chewing, and do not massage the area. You return to normal life the same day.
The timeline of the effect
This area runs on a different clock from the rest of the face. The reduction in chewing strength is felt in 1–2 weeks, but visible slimming does not begin until weeks 4–6.
The change in muscle volume reaches its most obvious point at around month 3. Judging the result in the first two weeks is misleading here; assessment is at weeks 4–6, which for a travelling patient means by photograph after you are home.
The effect lasts 6–9 months on average, longer than in the expression areas. As long as the clenching habit continues the muscle tends to return to its previous volume, so repeat treatment can be planned.
What decides the result
The result is decided by the injections staying inside the safe zone. Placement too close to the front and upper part of the muscle can affect the neighbouring muscles that control the smile and cause temporary asymmetry.
In the first weeks you may struggle with hard food. That is an expected effect and it eases as some muscle strength returns.
Width in the lower face is not always muscular. Where it comes from bone structure or fat, masseter treatment does not change that component. Loose skin in the jaw and neck is not corrected by it either.
Who this is not for, and what not to expect
Botulinum toxin is a prescription medicine with its own contraindications. A diagnosed jaw joint disorder, difficulty chewing or limited mouth opening must all be assessed before treatment.
Masseter treatment does not stop the clenching habit; it reduces the force the muscle can apply. The habit itself may continue, so measures such as a night guard are considered alongside it — and if you already wear one fitted where you live, bring it or a photograph of it.
- Pregnancy and breastfeeding — not treated
- Neuromuscular disease (myasthenia gravis, Lambert-Eaton syndrome, motor neurone disease) — not treated
- Aminoglycoside antibiotics — they can amplify the effect of the toxin; not treated until the course is finished
- Active infection or inflammatory skin disease over the jaw — not treated until it clears
- Known hypersensitivity to botulinum toxin — not treated
- Bleeding disorder or anticoagulant use — bruising is more likely; a doctor’s assessment is required
- No visible effect should be expected before weeks 4–6; bony jaw width and loose skin are not corrected by botulinum toxin
This page is general information and does not replace a clinical examination. The method, dose and timescale that apply to you are decided by a doctor after examining you.
Frequently asked questions
How many units does masseter treatment take?
When will I see the result?
Will it stop me clenching?
Will I struggle to eat?
How long does it last?
Pre-assessment
Describe your situation and we will answer with a measurement
Send a photograph or an X-ray. A doctor in the relevant speciality will reply with a graft range, a number of teeth or a dose range in units. If you are not suitable, we say so plainly.