Are multiple sessions of Botox injections needed for slimming the masseter muscle before results are noticeable?

You probably just need additional units. As with other areas of the face, there is a range of number of units that is effective for a given patient. I typically start with 25units per side but this can certainly be increased for the desired effect. If you didn't get before and after photos you should, as results can sometimes be difficult to see. Hope that helps and best wishes, Dr. Donath 

Yes, it can take multiple treatments of Botox to slim the masseter. Keep in mind, Botox results last 3-4 months. Radifequency treatments can help improve results. See an expert in facial contouring for a formal evaluation. Best, Dr. Emer

Thanks for this question.The doses for Masseter injection usually vary between 15-30 units per side. It's very unusual not to see a significant change in facial shape after the dose that you have received.It would not be unreasonable to try  it once more with the same dose. I would make sure that you have good photos to objectively asses the result.

Twenty units of Botox per side is a reasonable starting point, but it sounds as if you will need to have more to achieve the desired effect. I generally will start at 25 u per side and escalate the dose as necessary. 

Hi GDennison, thank you for your question! Botox is a great treatment for anyone who has large masseter muscles and is looking to slim their face. Injecting these muscles with Botox weakens them, causing them to decrease in size (atrophy), thus providing the slimming effect. However, it takes time for the muscles to atrophy, and depending on the size and strength of your masseters can also require multiple treatments. Botox is a temporary treatment which is why it is important to have treatments to the masseters every 4-6 months to maintain results and ensure that the muscles do not regain their strength. 
I've created a video where I review treating the masseter muscles with Botox. I hope you find this information helpful in your research!

Thank you for your question. Starting at 20 units per side is a practicable starting point. However, it does sound like you may need Botox to achieve your desired effect. You will need to have regular injections every 3-4 months to maintain your results. I recommend having a consultation with an expert injector to determine the best treatment plan for you. Best of Luck!

Botox takes about a week to even
begin having an effect.  The masseter is only partially weakened as it is
needed for chewing.  Therefore, often it will take several months and
possibly a few treatments to see a real noticeable difference for facial
shaping.

Botox to decrease the bulk of the jawline masseter muscle is the correct treatment for you.  You received a correct dosage, but you need to increase the frequency of your treatments and may possibly need a little more if you still felt the full ability to clench the muscle.Also- remember if you chew gum- Stop because this will work against the Botox.

I usually recommend 20-25 units per side for initial masseter injection. However, the dosing dose vary by the patient and muscle strength. The Botox works great when it comes to reducing masseter muscle bulk and slimming the lower face. Patient's usually require treatment every 3-4 months to keep the masseters relaxed and to keep the masseter bulk from reappearing. Overtime and with repeated treatment, the treatment intervals may increase to once every 4-6 months. 

Botox injections are done to reduce both the size and hyperactivity (bruxism) of one of the main chewing muscles such as masseter. The dose varies for each individual and is usually established based on size of a muscle. While 20 units appears to be a lower limit of an average dose, the repetition of the injection should produce a desirable result with proper time intervals. Also avoid chewing gum for it will surely contribute to a restoration of a muscle volume and its strength. Good luck