Opioid receptors


Opioid and opioid-like receptors are activated by a variety of endogenous peptides including [Met]enkephalin (met), [Leu]enkephalin (leu), β-endorphin (β-end), α-neodynorphin, dynorphin A (dynA), dynorphin B (dynB), big dynorphin (Big dyn), nociceptin/orphanin FQ (N/OFQ); endomorphin-1 and endomorphin-2 are also potential endogenous peptides. The Greek letter nomenclature for the opioid receptors, μ, δ and κ, is well established, and NC-IUPHAR considers this nomenclature appropriate, along with the symbols spelled out (mu, delta, and kappa), and the acronyms, MOP, DOP, and KOP. [1,2,3]. The human N/OFQ receptor, NOP, is considered 'opioid-related' rather than opioid because, while it exhibits a high degree of structural homology with the conventional opioid receptors [4], it displays a distinct pharmacology. Currently there are numerous clinically used drugs, such as morphine and many other opioid analgesics, as well as antagonists such as naloxone, however only for the μ receptor.


  1. Foord SM, Bonner TI, Neubig RR, et al. International Union of Pharmacology. XLVI. G protein-coupled receptor list. Pharmacol Rev 2005;57:279-88.
  2. Dhawan BN, Cesselin F, Raghubir R, et al. International Union of Pharmacology. XII. Classification of opioid receptors. Pharmacol Rev 1996;48:567-92.
  3. Cox BM, Christie MJ, Devi L, et al. Challenges for opioid receptor nomenclature: IUPHAR Review 9. Br J Pharmacol 2015;172:317-23.
  4. Mollereau C, Parmentier M, Mailleux P, et al. ORL1, a novel member of the opioid receptor family. Cloning, functional expression and localization. FEBS Lett 1994;341:33-8.
Excerpt from IUPHAR/BPS Guide to Pharmacology
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