I got masseter jaw reduction Botox 1 week ago and absolutely no changes whatsoever. My masseters are large and strong (Photo)

Botox blocks muscle activity. It typically takes up to a week to fully paralyze the muscle. At that point the muscle will slowly atrophy, or shrink. Depending on the individual, it may take several treatments to see the desired effect. So not to worry, you’re on your way. Ask your Injector to provide you the number of units injected, and keep track for future treatments. Botox lasts 3-4 months. Good luck.

Botox for the masseter muscles take time to show a result.  This is probably the toughest location to get good results. In my experience it can take months to see the results. The process is like putting the muscle in a "chemical" cast so that the muscle will shrink over time. For example, if you have a cast on your arm for 1 month and do not use it you will notice the muscles shrink. That is a physical cast but it is a good way to explain botox of the masseters.  It really does make a difference who is injecting, how much and where it is injected. It is one of those treatments that unfortunately has become a commodity and it really requires a bit more of an artistic finesse approach.  
We use the neuromodulators to target and soften the muscles without giving that frozen look.
Hope this helps,
Best of luck,
DrC

May take at least 2 weeks & upto a month to see appreciable difference.  The key is # units & placement of Botox.  So, be sure to follow up with your injector.
Best wishes,
Dr B

HI.  Nice to hear from you in Vietnam.  Usually the full effect of Botox takes about ten or so days so you may need to be patient for another day or two.  But, if the physician who injected these muscles did not use enough botox you could also just need for to get the desired effect.

Botox can take 2 weeks to work. This is when muscle paralysis sets in. Remember that Botox for the face is different to Botox for facial slimming/masseter reduction. What this means is that with facial Botox, once muscle paralysis occurs, the effects are easy to see. With facial slimming/masseter reduction, the visual effect takes a bit longer. This is because muscle paralysis has to set in. Then over time, the jaw muscles reduce in size (as it is paralysed and not being used) and the visual effect of jaw reduction is more apparent.
There is also the factor of having injected Botox in the right area. It is not a superficial injection like Botox for forehead wrinkles for example.

You typically need to wait 2 weeks to see the results of botox treatment.  In addition, the masseter is a large muscle compared to other facial muscles so typically require significantly more to see the desired results.  I recommend that you follow-up with your injector after 2 weeks and consider additional treatment for desired results.