I thought you'd like this, from a user "DiePilot" from the Ars Technica board, who is a medic with the military. He has these things called "fentanyl lollipops," which is a lollipop form of a painkiller drug with a potency approximately eighty times that of morphine.
I get the mega 800mcg ones, tape them to the casualty's thumb, and then tell them to suck their thumb when it hurts. They do this, then pass out eventually. Their thumb falls out of their mouth, and I don't have to worry about overdoses while they're in the helicopter.