The masseter muscle runs along your jawline near the ear. You can feel it if you clench your jaw tightly. It is used to move your lower jaw up and down and side to side.

Some people have overdeveloped masseter muscles, which can present as a wide, square jawline. Teeth grinding (bruxism) can result in enlarged masseters and and give significant jaw pain and headaches.


This can also cause facial asymmetries, or increased muscle bulk offering a masculine, squared look to the lower face. Injecting Toxin into this muscle will relax it, offering relief from teeth grinding and headaches due to the clenched jaw, reduce and slim down a square jaw, offering a more feminine contour to the lower face.

After injection, the muscle contractions are weakened, preventing the masseter muscle from contracting so much. Following the first treatment, the masseter muscle will atrophy (waste away slightly). This will result in the jaw line becoming more ‘v-shaped’ and less square.

A side effect you may experience is a reduction in jaw clenching and/or teeth grinding.

Some side effects include:

  • Temporary bleeding/bruising
  • Mild swelling
  • Post-treatment headache

More serious side effects can occur for the treatment of other areas (e.g. double vision, drooping lip, difficulty swallowing or breathing, change of voice or difficulty pronouncing some words.

DO NOT have injections if:

  • You are pregnant or breastfeeding
  • You are trying to get pregnant

You will also need to let your practitioner know if:

  • You have a muscular disease (e.g. Bell’s Palsy)
  • You have any blood or nervous system disorders
  • You are taking any medications which affect blood clotting
  • You are taking any medicines
  • You have any psychological concerns