The results usually start to be noticed within three to 10 days or even sooner. They tend to last in most people for up to three or four months. As time passes, the muscle activity will gradually return to normal. Additionally, other areas may return to activity over time, depending on the amount injected. The interesting thing about Botox is that it tends to work fairly well even up to the third month, as a procedure that might last a very short time at full strength and then go away quickly (filler injections such as Restylane, Perlane, or Juvederm tend to last approximately six to 12 months, depending on the amount used).
A double-blind, placebo-controlled study enrolled patients who had extended histories of receiving and tolerating BOTOX injections, with prior individualized adjustment of dose. The mean BOTOX dose administered to patients in this study was 236 Units (25th to 75th percentile range of 198 Units to 300 Units). The BOTOX dose was divided among the affected muscles [see Clinical Studies].
Spread of toxin effects. The effect of botulinum toxin may affect areas away from the injection site and cause serious symptoms including: loss of strength and all-over muscle weakness, double vision, blurred vision and drooping eyelids, hoarseness or change or loss of voice, trouble saying words clearly, loss of bladder control, trouble breathing, and trouble swallowing.