I speak only for myself here, but owing to one lot of medication I'm on these last 48 years, painkillers are not a no go for me. Between that and allergic/adverse reactions there's a lot they daren't do. The testicular cancer being the last surgical procedure carried out, deemed as life threatening due to the possibility of spreading. That operation didn't pass without incident.
Last painkiller used was on the last Saturday-Sunday in January 2012. stopped the heart, almost as soon as it was used. Resulted in two people ending their shifts filling in forms, explaining their actions. It's partly why I've the DNR on record, the other being I know there's limits on what they can do, without making things worse. I want no-one being blamed for it, should the same happen again.
Snapped the ankle in November 2000, resulting in having it set straight with no pain relief. They didn't want to risk it going wrong.