# Mu-opioid receptor

Source: https://onco.cc/targets/oprm1/  
OnCo record `oprm1` (Target). Data CC BY-NC 4.0, attribute "Data from OnCo (onco.cc)"; commercial use needs a licence.

## TL;DR

The mu-opioid receptor is the target of morphine and the other strong opioids that control most severe cancer pain; the same receptor in the gut causes opioid constipation, which methylnaltrexone and naloxegol relieve by blocking it outside the brain.

## Summary

Mu-opioid receptors in the spinal cord and brain mediate the pain relief of morphine, oxycodone, fentanyl and methadone, which remain the mainstay of the WHO analgesic ladder for moderate to severe cancer pain. The same receptors in the intestinal wall slow gut movement, so opioid-induced constipation affects most patients on long-term opioids; peripherally acting antagonists such as methylnaltrexone, naloxegol and naldemedine block gut receptors without reaching the brain, and methylnaltrexone is approved specifically for opioid-induced constipation in advanced illness. Whether opioids influence tumour growth or recurrence through receptors on cancer cells is an open research question.

## Fields

- Kind: Target
- Last checked: 2026-09-04
- Tags: chembl-gap
- Symbol: OPRM1
- Class: other
- Biology: A Gi-coupled G-protein-coupled receptor that closes calcium channels and opens potassium channels in neurons, reducing neurotransmitter release; densely expressed in dorsal horn, periaqueductal grey and enteric neurons.
- Where found: Central and enteric nervous system; Expressed on some tumour cells; significance under study

## Sources

- Wikipedia: https://en.wikipedia.org/wiki/Μ-opioid_receptor
- UniProt P35372: OPRM1: https://www.uniprot.org/uniprotkb/P35372/entry
- HGNC:8156 OPRM1: https://www.genenames.org/data/gene-symbol-report/#!/hgnc_id/HGNC:8156
- ChEMBL target CHEMBL233: https://www.ebi.ac.uk/chembl/explore/target/CHEMBL233

## Connected records

- drugs: [Methylnaltrexone](https://onco.cc/drugs/methylnaltrexone/)
- technologies: [Early integrated palliative care](https://onco.cc/technologies/palliative-care/)

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JSON: https://onco.cc/api/v1/entities/oprm1.json