A youth is brought into the emergency department by paramedics after being found unconscious lying on a sewer grate. No further history is available. In the triage unit, the patient’s respiratory rate is 8 breaths per minute, and the breaths are shallow. Heart rate is 50. Pupils are constricted and fixed. “Track marks” are noted on the forearms. The triage nurse applies oxygen by mask, inserts a peripheral intravenous line (with some difficulty), and pages the emergency department resident urgently. The resident administers a medication through the intravenous line. Three minutes later the patient is awake and complaining of generalized pain. Respiratory rate is 20. The emergency resident pages the internal medicine resident to admit the patient to hospital for monitoring. When the internal medicine resident arrives at the bedside an hour later, the youth is once more unconscious, breathing slowly and shallowly as on arrival in triage.