What is the constellation of effects associated with mu receptor opioid subtypes in the pathophysiology of opioid abuse?

Updated: Jun 21, 2018
  • Author: David W Dixon, DO; Chief Editor: Glen L Xiong, MD  more...
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More than 20 clinically available medications bind opioid receptors. Most of these are prototypical mu receptor full agonists (capable of producing a maximal response at mu receptor subtypes in opioid-sensitive systems), and are associated with the following constellation of effects:

  • Pain relief

  • Mood alteration (often producing euphoria and decreased anxiety)

  • Respiratory depression (can cause death in overdose)

  • Decreased gastrointestinal motility (can cause constipation)

  • Cough suppression

  • Suppression of corticotropin-releasing factor and adrenocorticotropin hormone

  • Pinpoint pupils (miosis)

  • Nausea, vomiting, pruritis (less common)

Almost all abused opioids are prototypical mu agonists. The euphoria associated with mu receptor activation is often termed a high. Moreover, when opioids are injected or inhaled, levels in the brain rise rapidly, causing a rush or thrill. The rush is a brief, intense, usually pleasurable sensation, which is followed by a longer-lasting high. When opioids are used chronically, tolerance and physical dependence occur. Over time, those with physiologic dependence often try to avoid unpleasant withdrawal symptoms rather than seeking the pleasurable sensations associated with initial use of opioids.

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