I am not like that. I can usually take a low dose. The one time I had to have a high dose was when I had let tooth infection go too long before removing the tooth, because it did not hurt....then, they could not give me enough to numb the pain.

I have a genetic problem with the P-450 system, MrsD. In my case, it's called Porphyria. I did not know that other people besides porphs had this problem. We do not detox meds quickly, that is, the ones which challenge the p-450 system either "up" or "down". But some meds do NOT challenge that system.
For instance, i cannot take Lidocaine but can take Marcaine and Carbocaine. Very very large difference in reaction.
I cannot take many pain pills, but can take Demerol, although fortunately I have not had to take it much in recent years.
Without the diagnosis, I was in the dark for most of my life, wondering if a drug would poison me or not. When I saw the safe/ unsafe drug list, I knew I probably had Porphyria. But it's very hard to get diagnosed, due to many many factors. Doctors are inexperienced. Labs are inexperienced in how to handle test materials which they send to a specialty lab. Doctors are not experienced in reading test scores. Doctors ascribe symptoms to other causes, like saying Ab pain must be colitis, and never test at all for Porphyria. I'm in good company, though (put that "good" in quotes) as royals have this disease. One royal who admitted it was Prince William of Gloucester, a handsome man who died in a plane crash at 30; google his name and find a touching Youtube history of his life, and see a man who looked like a movie star, and who had Porphyria inherited from one or both of his parents.