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Updated: Feb 24, 2026

Assessment of Morphine-induced Hyperalgesia and Analgesic Tolerance in Mice Using Thermal and Mechanical Nociceptive Modalities
Published on: July 29, 2014
Basics of Opioid Pharmacology
John Hansen1,2
1Sanford Pain Center, Sioux Falls, South Dakota.
Abstract:
The use of opioids in the treatment of chronic nonmalignant pain is neither endorsed nor proscribed by evidence-based medicine, except for the finding that opioids have certain risks. Also challenging for clinicians are consensus definitions for opioid pharmacology which are poorly chosen, changing, or euphemistic. This paper collects opioid consensus definitions for addiction, physical dependence, tolerance, and withdrawal, and offers practical discussion of the concepts they address. Addiction is a short-circuiting or overdrive of the mesocorticolimbic system of the brain. Physical dependence on opioids means that after chronic opioid dosing an abrupt cessation or marked dose decrease causes an opioid withdrawal syndrome. Physical dependence and addiction are unrelated neuroplastic phenomena which occur in different parts of the brain. Tolerance means a decreasing drug effect for a given dose over time. This applies to desired drug effects and to drug side-effects.
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