Masseter botox injection last week and it's been about 7 - 8 days now and so far no results?

Thank you for sharing your concerns about your recent Botox treatment. On average, Botox can take up to 2 weeks to take full effect in the treated muscles. For the masseters, it will likely take a few additional weeks before you notice the muscles themselves slimming down. I recommend waiting another week and then following up with your injector for evaluation. Depending on his/her assessment of the strength of the muscles, you may need to add additional units to achieve optimal results. In order to maintain your results, the procedure should be repeated every 3-4 months. Best of luck!

The massater muscles are much stronger than those in the forehead. It can take anywhere from 2-7 weeks to start seeing results. With Botox for the massater, it usually takes several treatments for results to become noticeable and to start noticing slimming of the jawline. These are usually spaced at 3 months apart.

Hi Christine.
For the masseter muscle to atrophy and for you to see results it's going to be several weeks. I also think best results are achieved after you have had a second injection about 3 to 4 months following your first injection. 
Best wishes, Dr. ALDO