I have been injecting Botox for cosmetic reasons for over twenty-two years. Since its ground-breaking entrance onto the nonsurgical aesthetic stage at that time, much has been learned about storing, mixing and injecting Botox (as well as the other more recent neuromodulators, Dysport and Xeomin). We now know that rigidly refrigerating these materials immediately before injection is not necessary for keeping them stable and effective, nor is it necessary to reconstitute them with preservative-free saline solution. Injecting with conventional sized needles, refrigerated solutions, and those containing preservative-free saline simply hurt more. Naturally hitting bone, striking sensitive nerves and nicking underlying blood vessels with hematoma formation from poor technique or lack of a good appreciation of the anatomy of the regions being injected are other potential causes of pain or discomfort.
To reduce the discomfort of the injections we can use especially small, narrow-gauge needles, we can allow the reconstituted material to come to room temperature, and we can reconstitute it with preservative-containing saline mixed with a small amount of local anesthetic and epinephriine (the latter being included to diminish the likelihood of bruising).
Of course, it goes without saying, that treatment should only be obtained from a board certified aesthetic physician experienced in the proper preparation and injection techniques for these materials.