First, the amount of BOTOX is not as important as the dilution. If the same amount of BOTOX was administered but the dilution was increased, you would have received fewer units. Different physicians utilize different dilutions. Some of us, including myself, use different dilutions in different areas. For instance, I like the least dilution possible if I am injecting under the eye or around the mouth. I want precision and do not want diffusion. This would require a dilution of I cc in a 100 unit vial. I have seen some excellent BOTOX adminstrators use a 10 cc dilution very effectively. This physician was adminstering 10 times the amount of BOTOX as I was, but the effect would be roughly the same since the units are the same. If your physician was indeed using the same number of units each time. There could be other factors at work. He/She might have used a different diluent. Allergan still recomends in their product insert to use non-reserved saline. Maybe the physician had a pang of guilt that he/she was doing something off label ( nearly all of us use presserved saline by the way), and decided to use unpreserved saline the second time. This does not last as long, hence is weaker, and might account for the less powerful effect. Also, the preserved saline uses benzyl alcohol as its perservative. This has an anesthetic quality to it. Using a preservative leads to less painful injections. You would have had the benefits of this less painful experience, the first time, but if the diluent was switched to unpreserved saline, not the second time. Finally, perhaps a different needle was used. Your injector might have used a 31 gauge needle the first time. Found it difficult to use ( it is a little bit, since it requres less pressure and BOTOX can leak out), and switched to the 30 gauge needle. The larger gauge needle being a bit more painful. We are all speculating here. It would be much easier to voice your concerns and questions, the the physician who injected it and the mystery would be solved.