Mu Opioid Receptor
The primary opioid receptor subtype responsible for the analgesic, euphoric, and respiratory depressant effects of traditional opioid drugs. Mu receptor activation carries significant risks of dependence and abuse. Peptide drugs like difelikefalin are specifically designed to avoid mu receptor activation.
Technical Context
MOR is the primary target of classical opioid analgesics (morphine, oxycodone, fentanyl) and endogenous beta-endorphin. MOR activation in the brain produces potent analgesia, euphoria, and reward — these effects underlie both therapeutic utility and abuse potential. MOR activation also causes respiratory depression (the primary cause of opioid overdose death), constipation, and physical dependence. The development of peptide drugs that selectively avoid MOR activation (such as difelikefalin's KOR selectivity) or that target opioid pathways peripherally represents an important strategy for providing pain relief and related therapeutic effects without opioid-class adverse effects.