Jawline Slimming with Botulinum Toxin: A Detailed Guide

Part of our complete guide to Anti-Wrinkle Injections.

Last updated: 9 August 2026

Jawline slimming with botulinum toxin has become one of the fastest-growing aesthetic treatments in the UK. This offers a non-surgical solution for patients seeking a more refined, V-shaped facial contour. By targeting the masseter muscles, the powerful muscles responsible for chewing, practitioners can reduce the width of the lower face, creating a slimmer, more elegant jawline without surgery.

Understanding the masseter muscle

The masseter is one of the strongest muscles in the human body relative to its size, generating significant force during chewing and clenching. In some individuals, this muscle becomes hypertrophied (enlarged) due to habitual clenching, bruxism (teeth grinding), or genetic predisposition, creating a square or wide jawline appearance.

How jawline slimming works

Botulinum toxin (commonly Botox, Azzalure, or Bocouture) is injected directly into the masseter muscle at strategic points. The toxin temporarily weakens the muscle, causing it to gradually reduce in size through a process called disuse atrophy, similar to how any muscle shrinks when it is not exercised.

Dr Michael Thornbury, maxillofacial surgeon and aesthetic practitioner, explains: “The treatment works with the body’s natural physiology. By reducing the signals that cause the masseter to contract forcefully, the muscle gradually slims over 4-8 weeks, creating a naturally refined jawline.”

The dual benefit: Aesthetics and function

Beyond cosmetic improvement, masseter botulinum toxin treatment offers significant therapeutic benefits:

• Bruxism relief: Reduces teeth grinding and clenching that damages dental work
• TMJ pain reduction: Alleviates temporomandibular joint discomfort and associated headaches
• Tension headache relief: Reduces muscle tension that contributes to chronic headaches
• Dental protection: Decreases force on teeth, reducing fracture risk and wear

Treatment Process

Consultation and Assessment

Your practitioner will assess your masseter muscle size by asking you to clench your jaw whilst palpating the muscle. They will evaluate facial proportions, discuss your goals, and determine the appropriate dose.

During Treatment

• Treatment takes approximately 15-20 minutes
• Typically 25-50 units of botulinum toxin per side (varies by muscle size)
• 3-6 injection points per masseter muscle
• Minimal discomfort, most patients describe a brief pinching sensation
• No anaesthetic usually required

Results Timeline

• Week 1-2: Reduced clenching force; bruxism symptoms begin to improve
• Week 4-6: Visible slimming of the jawline becomes apparent
• Week 8-12: Maximum slimming effect achieved
• Month 4-6: Effects begin to gradually wear off

Aftercare and Maintenance

• Avoid rubbing or massaging the jaw area for 24 hours
• No strenuous exercise for 24 hours post-treatment
• Avoid excessive chewing (chewing gum, tough foods) for the first week
• Repeat treatments are typically needed every 4-6 months initially
• Many patients find they can extend intervals over time as the muscle adapts

Who is a good candidate?

• Individuals with visibly enlarged masseter muscles creating a wide or square jawline
• Patients with bruxism or TMJ disorder seeking relief alongside aesthetic improvement
• Those desiring a more tapered, V-shaped facial contour
• Patients looking for a non-surgical alternative to surgical jaw reduction

Potential side effects

• Common: Mild bruising, temporary tenderness at injection sites
• Uncommon: Slight asymmetry (correctable at review), temporary difficulty with hard foods
• Rare: Paradoxical bulging (if toxin migrates to adjacent muscles), temporary smile changes

Frequently asked questions

Will masseter Botox affect my ability to chew?

The treatment reduces the muscle’s maximum force but does not eliminate chewing ability. You may notice that very hard or chewy foods require slightly more effort for the first few weeks, but normal eating is unaffected.

How many sessions are needed to see results?

Most patients see noticeable slimming after one session, with optimal results after 2-3 sessions. Regular treatments produce cumulative effects as the muscle progressively reduces in size.

Is jawline slimming permanent?

Individual sessions are temporary (4-6 months), but consistent treatment over 2-3 years can produce semi-permanent changes as the muscle atrophies. Some patients are able to significantly reduce their treatment frequency after this period.

Can jawline slimming be combined with other treatments?

Yes, it pairs well with chin filler for enhanced profile definition, jawline filler for overall contouring, and anti-wrinkle injections for other facial areas, all of which can be performed in the same appointment.