Are there some people Botox for masseter will not work on?

If the primary area of wideness corresponds to the area under the jawline muscle (masseter muscle), it's worth trying botox to shrink the muscle. If the wide area is closer to the chin, then botox will not help.

This is tough to answer without pictures. Even with a square jaw, Botox can help reduce and shape the jawline. I recommend getting a formal consultation with a cosmetic dermatologist. Best, Dr. Emer

The dose, the technique and post importantly, the shape of your face has a bearing on the result.  Sufficient botulinum toxin agent is need for the clinical effect.  I typically start with 12 units of botox on each side.

Thank you for your question. Botox will always work on the masseter muscles. Although, there is people who Botox to the masseter who it does not work. This is because a wide facial shape may not be because of enlarged masseter muscles. If the patient has a bony wide jaw then reducing the masseter muscle will not make a difference. 

If the cause of square face shape is masseter hypertrophy, then the Botox will help. If the shape is the result of the flaring of the jaw bone, then Botox will likely not provide the results you are looking for. That being said, most cases that I have seen in my clinic, Botox helps. I recommend you see an experienced injector for an in-person consultation.

You are correct that botox to the masseters will not significantly change a wide jawline if the majority of the shape is due to bone. This would require a jaw shaving or jaw reduction procedure for a permanent change. It is important to have an in-office examination to determine if this type of procedure is necessary and safe to achieve your goals. Hope this helps!Johnson C. Lee, MD Plastic Surgery

Yes and no. No, because the Botox will always work to weaken the masseter muscles. However, yes, there are people who it "doesn't work for" because the reason for wide facial shape may not be because of an enlarged masseter muscle. If the person has a wide bony jaw, reducing the muscle will not make a huge difference. 

If the problem is simply bone structure, the Botox injection won't work at all. It works if the muscle is enlarged and that can be determined at the time of consultation. It should work in most cases if the injection is properly done and the dosing is correct.

Botox (like Dysport and Xeomin) is a medication injected into target muscles of the face to selectively relax them for fewer/softer wrinkles or smaller muscles. Botox has been injected into the masseter muscle to slim the jawline. This only works in patients who have a square/wide jawline from a large muscle. Patient who have a wide jaw bone will not have any benefit from a Botox injection. Also, the injection does not work quickly. It may take over 6 weeks to see a result.  Seek out a doctor who can examine you and determine if Botox to the masseter muscle is appropriate for you. Safety comes first. 

I would be surprised if Botox doesn't help a little.  Even if the problem is a square jaw angle (which is most often the case), Botox should help.  The masseter goes all the way down to the corner of the angle.  Reducing this part of the masseter will make the square jaw angle not so obvious.  Of course, the best option is to reduce the bone.  We almost always do this without any external incisions.  Best wishes.