I have been doing research this morning on the use of epinephrine (adrenalin) in dentistry. Dentists are now mixing epinephrine with the ___caine anesthetics. The reason for this is that it prolongs the window of time for a dentist to work without the patient experiencing pain - a significant amount of time from about 15-20 minutes to 1-2 hours. However, what many dentists may not be aware is that there are some patients for whom this could be life-threatening. If a patient has heart disease, diabetes or thyroid disease, administering epinephrine can produce a fatality. I share this not because I want to scare anyone, but because I do not want anyone to unnecessarily suffer the trauma I had on the dental table. I have thyroid disease and while not diabetic, am "insulin resistant."
If you have any of these conditions, Google your condition along with the keywords "dental epinephrine" and print them out and take them to your dentist to discuss with him before you have dental anesthesia.
Been there, done that...so NOT fun.