My father was in a lot of pain before he died. They used fentanyl patches to administer the drug. It is absorbed through the skin. That said, I haven’t a clue how much would have to be absorbed to kill a person.
The patches were from 25 for non opioid tolerant and 50 and higher for others. They lasted 3 days. They were not like these street pills that police tell us are much stronger.