It can be true for untreated Graves' patients cause Novacane, cocaine or any "caine" for that matter can increase blood pressure and heart rate slightly, which is probably already high because you have Graves'.
The "caines" are very similar to adrenaline. It constrics vessels, increases heart rate and blood pressure - something you certainly do not want if you are already hyper and experiencing problems. For me, even a litle novacaine seems to set off panic attacks, but everyone is different. The amount they use to drill a tooth is pretty small, but you should probably let your dentist know if you've got Graves'.
You have to check, but beta blockers might be contraindicated with the "caines" so if you are on beta blockers and need to get a tooth drilled, be sure to tell the dentist first....you need to check with a doctor but I believe a mixture of the two can send your BP way high.