Opioid receptors

Opioid receptors are currently classified into three groups, κ, δ and μ receptors. Subtypes within each group have been suggested including μ1, μ2, δ1, δ2, κ1, κ2, and κ3. An opioid-like receptor with a high degree of homology to μ, δ and κ-opioid receptors has been cloned and termed the orphan opioid receptor (NOP, ORL1). This receptor has a distinct pharmacological profile from the classical opioid receptors and an endogenous ligand, nociceptin, also known as orphanin FQ has been identified. Opioid receptors are activated both by endogenously produced opioid peptides and by exogenously administered opiate compounds, some of which are the most effective analgesics known but also highly addictive drugs of abuse.

Opioid receptors categories

δ Opioid receptors κ Opioid Receptors

μ Opioid receptors Nociceptin receptors

Further reading

Waldhoer et al (2004) Opioid receptors. Annu. Rev. Biochem. 73 953 PMID: 15189164

Stein (2016) Opioid Receptors. Annu. Rev. Medicine 67(1) 433 PMID: 26332001

Wang (2019) Historical Review: Opiate Addiction and Opioid Receptors. Cell Transplantation. March 2019 233 PMID: 30419763

Seppälä et al (2025) Endogenous opioid system modulates proximal and distal threat signals in the human brain. Mol Psychiatry https://doi.org/10.1038/s41380-025-03385-3

Related Targets

Adhesion class receptors Adrenergic receptors Cannabinoid receptors Chemerin receptors Chemokine receptors Dopamine receptors

Frizzled receptors G protein-coupled estrogen receptors Orphan 7-TM receptors Peptide receptors Serotonin receptors

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Pharmacology

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Research Area

Pharmacology

Type

Research Area

Pharmacology

Type

Research Area

Opioid receptors