Just to offer a little balance. Pain meds are addictive. It is perfectly possible to have real chonic pain and be addicted to pain medication. While by no means does everyone who is put on pain meds become addicted, many do. I work with addicts all the time. Addicts lie. So saying that the patient must be the sole judge of their pain sounds a bit simplistic to me.
This is a major issue treatment issue which should be addressed by the treatment team, not left up to the individual judgement of nurses. It is possible, even likely, for nurses to become cynical, particularly in high stress situations. Patients sometimes inadvertently trigger that cynisism. I recall once when I worked in the er, we had a woman who came in with a c/o vague but intense abdominal pain, but with a affect that seemed too controled and calm. She kept asking for, "something for pain". The ER staff, from the Doc on down, interperted this as learned "hospital jargon" and evidence of drug seeking. They treated her appropriately, drawing lab work etc. but with no sense of urgency and no pain meds. Until, that is, her her CBC came back low! Turned out she had a preforated gastric ulcer. She had a hole in her stomach the size of a quarter.