What is masseter Botox and what is it for?
It is the injection of botulinum toxin into the masseter muscle at the angle of the jaw to temporarily reduce its strength. The main reasons are muscle tension from clenching and a wide jaw angle caused by muscle bulk.
The masseter is a powerful muscle that closes the jaw when you chew. In people who clench or grind their teeth, by night or by day, it can become more prominent and cause tightness at the jaw angle or a tired feeling in the morning. When botulinum toxin reduces the muscle’s strength, clenching force decreases and, over time, the muscle may also become less bulky. Treatment can therefore be considered for both functional and aesthetic reasons.
Clenching and grinding have many causes, including stress, sleep patterns and how the teeth meet. Botox reduces muscle force but does not remove the underlying cause. If you have tooth wear, jaw joint pain or difficulty opening your mouth, assessment with a dentist or the relevant specialist may be needed. Treatment may also be planned alongside measures such as a night guard.
Does masseter Botox slim the face?
If the width at the jaw angle comes mainly from a strong masseter, the lower face can look slimmer as the muscle reduces. If the width is due to bone structure, fat or sagging, this effect should not be expected.
At your consultation you will be asked to clench so the muscle can be assessed by sight and touch. Where the width is muscular, the muscle reduces gradually over the weeks after treatment, so any change in shape appears slowly, usually over several weeks to a few months rather than straight away. How much change you see depends on the size of the muscle to begin with and the dose used.
Fullness in the lower face can also come from a broad jawbone, cheek fat, a double chin or age-related sagging. In these cases masseter Botox will not meet expectations and, in the wrong face, may even create a hollow look below the cheeks. Where appropriate, treatments for the double chin, fillers or energy-based devices are considered separately. An accurate diagnosis is the basis of realistic expectations.
Who may not be suitable for masseter Botox?
Treatment is not given, or is postponed, during pregnancy and breastfeeding, in neuromuscular conditions, when there is infection in the area and in anyone allergic to the ingredients. People with a slim face or hollow cheeks need particularly careful assessment.
Treatment is not carried out in neuromuscular conditions such as myasthenia gravis, or during pregnancy and breastfeeding. Certain medicines that affect muscle transmission, and recent dental or jaw surgery, may also affect timing. If you have active jaw joint pain or limited mouth opening, the cause is investigated first. If there is a skin infection at the injection site, it needs to heal beforehand.
In people whose face is already slim, or who have lost volume in the mid-face, reducing the masseter can make the area below the cheekbones look more hollow. Eating a lot of hard foods, chewing gum habitually or speaking extensively for work are also taken into account. With this information, whether treatment suits you, what dose to start with and what to expect are clarified at your consultation.
How is masseter Botox done, and what is the aftercare?
The borders of the muscle are found by asking you to clench, and a few points are injected on each side. For the first day, avoid massaging the area, strenuous exercise, saunas and hammams.
Before treatment, the front and back borders of the muscle and a safe injection zone are marked. Injections are placed in the lower and middle part of the muscle, away from the smile muscles, to limit unwanted spread. The procedure is short. A reduction in chewing force is usually felt within a few days, while the change in shape progresses more slowly and becomes noticeable over the following weeks.
In the first few days you may notice mild fatigue when chewing hard or tough foods; this is usually temporary. Avoid rubbing the area and lying face down for the first few hours. A review is usually arranged a few weeks later to check the balance between the two sides, and the timing of any repeat treatment is planned then. If you are visiting Istanbul, agree in advance how this review will be arranged.
What are the risks, and how long does masseter Botox last?
The most common effects are temporary chewing fatigue, tenderness and bruising; less often, the smile may look uneven. For most people the effect typically lasts around 4–6 months, though this varies.
If the toxin affects the nearby smile muscles, the smile can become temporarily uneven. Occasionally only part of the muscle relaxes, leaving a noticeable bulge when chewing. A hollow look in the lower face may occur, particularly in slimmer faces. These effects are usually temporary but can last for several weeks until the toxin wears off, and any of them should be raised at your review.
Because the masseter is a large, strong muscle, results sometimes last longer than in the upper face. In some people treated regularly, the muscle bulk returns less fully over time, which can affect how often treatment is needed. Even so, the duration cannot be predicted precisely in advance. The timing of the next treatment is decided by assessing how the muscle has recovered.
Frequently asked questions
Will masseter Botox stop me clenching completely?
Botox reduces clenching force but does not remove the underlying cause of the habit. The effect is temporary; if you have tooth wear or jaw joint symptoms, assessment with a dentist is advised.
When will I notice my face looking slimmer?
Reduced chewing force can be felt within a few days. Any change in shape follows the reduction in muscle bulk and appears more slowly, usually over weeks.
Will it make eating difficult?
You may feel mild fatigue with hard foods in the first weeks. The dose is planned so that normal eating is not restricted; any unexpected difficulty is assessed at your review.
Can masseter Botox affect my smile?
When injected at the right points, the aim is for the smile muscles to be unaffected. Occasionally, spread to nearby muscles can cause a temporary asymmetry.
Can masseter Botox be combined with chin filler?
In some faces the two may be planned together for lower-face balance. Whether both are needed, and which comes first, is decided at your consultation.
How many masseter Botox sessions will I need?
Masseter Botox works after a single session, but the effect is temporary and the muscle gradually regains its strength and bulk. To keep clenching controlled or maintain the jawline change, masseter Botox is usually repeated as the effect fades, roughly every 4–6 months for most people. After regular treatments, muscle bulk returns more slowly in some people, so the interval may be extended.
Can masseter Botox replace my night guard?
No, masseter Botox does not replace a night guard; the two do different jobs. A night guard mechanically protects the teeth from the wear caused by clenching and grinding, while masseter Botox temporarily reduces clenching force. If you have tooth wear, broken fillings or crowns, or jaw-joint symptoms, the two can be planned together following your dentist’s assessment.
Can masseter Botox help headaches caused by jaw clenching?
Masseter Botox may ease clenching-related jaw-muscle pain, and the tension that spreads to the temples, in some people, but not everyone notices this effect. Headaches can have other causes, such as migraine, tension-type headache or jaw-joint problems. If you have limited mouth opening, a jaw that locks or a new, severe headache, the cause of these symptoms is assessed separately first.
Can masseter Botox make the face sag?
Masseter Botox does not cause sagging in most people. However, in people with reduced skin elasticity or mid-face volume loss, laxity in the lower face or hollowing below the cheeks can look more noticeable as the muscle shrinks. That is why age, skin quality and overall facial support are assessed beforehand, and a lower dose or another method is discussed if needed.
Sources (3)
- Ferrillo et al., Toxins (Basel): The Role of Botulinum Toxin for Masseter Muscle Hypertrophy: A Comprehensive Review (2025)
- International Botulinum toxin Advisory board (Ascher et al., Aesthet Surg J): International Consensus Recommendations on the Aesthetic Usage of Ready-to-Use AbobotulinumtoxinA (Alluzience) (2024)
- Global Aesthetics Consensus Group (Sundaram et al., Plast Reconstr Surg): Global Aesthetics Consensus: Botulinum Toxin Type A--Evidence-Based Review, Emerging Concepts, and Consensus Recommendations for Aesthetic Use, Including Updates on Complications (2016)
This content is for general information and does not replace a personal medical assessment.