Opioid receptor mu-type 1 (MOR (also known as OPRM1))

The Opioid receptor mu-type 1, also known as mu opioid receptor, is a member of the G protein-coupled receptor family encoded by the *OPRM1* gene. It is primarily expressed in neurons throughout the nervous system. This receptor serves as the main binding site for endogenous peptides like beta‐endorphin and enkephalins, which regulate pain perception, reward mechanisms, mood, stress response, and addictive behaviors. It is also targeted by exogenous opioids—including prescription analgesics such as morphine, oxycodone, fentanyl, methadone—and illicit drugs like heroin. Activation leads to inhibition of neurotransmitter release via Gi/o protein signaling pathways. The mu opioid receptor plays a central role in mediating both therapeutic effects such as analgesia and adverse outcomes including tolerance development, physical dependence/addiction liability, respiratory depression risk during overdose situations. Genetic variants like A118G can influence individual differences in drug response and vulnerability to substance use disorders.

Other names

Mu opioid receptorMu opiate receptorMORMOPM-OR-1LMORMOR1OPRM1

Drugs targeting this molecule typically act as: Agonists—activate the mu opioid receptor to produce analgesia and euphoria (e.g., morphine, fentanyl); Partial agonists—partially activate the receptor with a ceiling effect on efficacy (e.g., buprenorphine); Antagonists—block the effects of opioids at this site to reverse overdose or prevent abuse (e.g., naloxone)