One of my masseter muscles are bigger than the other?

Botox can help to even masseter muscle asymmetry. Seek a consultation with an expert injector to ensure you receive the look you desire. All the Best. 

Botox can work to even the asymmetry.  I suggest getting a formal evaluation first to ensure there is no gland hypertrophy.  Although, I routinely treat parotid hypertrophy in my HIV patients with botox with great success.  Best, Dr. Emer.

I would get an examination by your doctor to make sure that it is indeed the masseter muscle that is enlarged. The parotid gland is in that area as well, and it may be that it is enlarged due to some other process.  A routine head and neck exam can confirm that it is the masseter.  If it is indeed just masseter hypertrophy, Botox can address this or you can chew more on the other side to strengthen the side that is smaller.

Hi Mason330, great question! It's very common for individuals to have asymmetrical masseters. This is something that can be fixed with Botox. Injecting Botox into the muscle weakens it, and over time while the muscle is weaker it atrophies (decreases in size), providing the slimming effect. Once the effects of Botox wear off, the muscle will begin to function more frequently and regain its strength, slowly increasing in size again, which is why I recommend treatments every 6 months initially. Many patients report that with time they need treatments less frequently. 
I've created a video that reviews treating masseter muscles with Botox. I hope this is helpful in your research! 

Botox works very consistently and well in this area and it is a very effective way of improving (notice I didn't say curing!) the asymmetry. Of course, it is important to be evaluated by someone with experience in both operating and injecting in this area because other anatomical variants can also demonstrate themselves in this manner. Once this is confirmed to be the case, however, a moderate amount of botox injected into the LARGER or bulkier muscle is very helpful to treat it. The botox may wear off around 3-4 months, so will likely need reinjection a few times a year to maintain results.Alternatively, if you would rather increase the size of the smaller muscle, there are a few options. One is to have fillers injected deeply onto the bone to help volumize the smaller side. Some patients choose to have Sculptra injected (which works by stimulating collagen over time) and others choose fillers like radiesse or juvederm to achieve this result within a shorter period. There are no FDA-approved injectables for this area, so it's important to use someone with plenty of experience.Finally, there are jaw implants that are permanent and can be placed through incisions in the mouth to help improve symmetry on the smaller side. Most patients prefer to use injections initially, and if they are happy with the symmetry, and need a more permanent solution, will have an implant placed.Best of luck in your quest!

Patients love Botox for this problem. If you can change your chewing habits, you may not need to continue Botox after you have achieved symmetry.

Almost every human has some degree of asymmetry to their faces. There isn't a great way to increase the smaller muscle immediately, but you could have a very limited amount of Botox done to the larger muscle to help shrink it. You could also make a conscious effort to chew on the other side and see if that makes your jaw muscle on that side any bigger. Sometimes years and years of doing one thing is hard to counteract. "This answer has been solicited without seeing this patient and
cannot be held as true medical advice, but only opinion. Seek in-person
treatment with a trained medical professional for appropriate care."