Actually when I had oral surgery in 1999 I told them about all the medications I took (neccessary before any visit to a doctor you haven't seen) and they gave me the injection of novacaine without that chemical so they are aware of that. Of course I didn't need general anaesthesia because it was just to remove a cyst and in a way it was easier then because the medications I was taking were more known clinically (Lamictal and Seroquel) but they can and will accomodate this.
You should let your dentist know, it's not ephedra but many freezing agents have adrenaline to get the freezing to work faster. I have to take extra ativan to counteract that. Ask your dentist what you need to do, or is there another alternative to it available.