From what I understand the vomiting is normal when you give an animal de-worming herbals--it's part of their detox process. Of course, I am assuming you are giving him the correct dose for his body weight? You don't want to over do it. My hopes is that you will try not to overwhelm kitty. Maybe let him get through his course of parasite herbals before going at him with the zapper? Just a thought. I have zapped my kitty a few times. I let her sit on my lap and put the copper paddles underneath her belly. She doesn't seem to mind.