The physiology and pharmacology of pain: a review of opioids.

Patients in the postoperative period are often inadequately medicated for pain. Appropriate nursing assessment and intervention is critical for controlling a patient's pain and preventing associated complications. Nurses must understand the physiology of pain and the pharmacology of the drugs used. This article reviews the physiology of pain and the pharmacology of opioids. The three classes of opioids-opioid agonists, opioid agonist-antagonists, and opioid antagonists-are examined in detail. Included in the discussion are opioid receptor interaction with the various agents, dosages administration, and side effects.