Thank you for your question. Botulinum Toxin (Botox, Azzalure, Dysport etc)is effective in reducing temporarily the strength and to a certain extent the bulk of muscular tissue. Its off-label use ranges from crow's feet area, upper lip, chin and also in the reduction of the square jaw (botox jaw reduction) when result of hypertrophy of the masseter muscle. I agree that with the correct indication and in the right hands, it is an extremely effective treatment with a very high degree of satisfaction.
I hope it helps
Web reference: http://www.andreamarando.com/botoxjawreduction.html