I am so sorry to hear this and so very angry that they didn't tell you about possible side effects. I've been thinking about it since last night when I read your post. It is so upsetting. Poor Onyx! As we know there are many special needs kitties and doggies on this site and they all do well, but it is unfortunate that this happened due to a vets lack of giving you information and allowing you to make a decision. I gave the same to my Gidget not knowing that there were side effects and we were lucky, but how many like your Onyx are not!! My heart goes out to you and her. Good thoughts and prayers that she will adjust quickly!