More often than being directly related to the medication, patients often experience nausea as a result of the procedure itself. We call this a "vaso-vagal reaction." This is just a reaction to the procedure you're undergoing, as much as you are nervous about the procedure and how well you tolerate such a thing. This reaction, which can include lightheadedness, disorientation and weakness, nausea, and sweating, usually lasts only a few minutes (most patients are good to leave, in the infrequent instances this occurs, after about 10-15 minutes of rest and foot elevation).
If you have this same reaction with other procedures, such as biopsies, blood draws, other injections or even ear exams, you should let your dermatologist or plastic surgeon know that this has been a problem in the past PRIOR to starting the treatment. This way, we can be prepared to help you in the event that it occurs, and we can coach you through it. Depending on the severity, we may even recommend against it. In any case, Botox is generally a short procedure and you
As far as nausea from the medication itself, the duration of that cannot be determined ahead of time and this is an infrequent cause. Let your practitioner know how you are doing; communication is key.