Challenges for opioid receptor nomenclature: IUPHAR Review 9


  • The authors are all members of the NC-IUPHAR Opioid Receptor Nomenclature Subcommittee who were present at the 2013 INRC meeting.
  • This review is submitted for publication in the special volume of the British Journal of Pharmacology with reports from the 2013 meeting of the International Narcotics Research Conference held in Cairns, Queensland, Australia, July 2013.
  • This article, written by members of the International Union of Basic and Clinical Pharmacology Committee on Receptor Nomenclature and Drug Classification (NC-IUPHAR) subcommittee for the opioid receptors, confirms the existing nomenclature for these receptors and reviews our current understanding of their structure, pharmacology and functions and their likely physiological roles in health and disease. More information on this receptor family can be found in the Concise Guide to Pharmacology ( and for each member of the family in the corresponding database.


Recent developments in the study of the structure and function of opioid receptors raise significant challenges for the definition of individual receptor types and the development of a nomenclature that precisely describes isoforms that may subserve different functions in vivo. Presentations at the 2013 meeting of the International Narcotics Research Conference in Cairns, Australia, considered some of the new discoveries that are now unravelling the complexities of opioid receptor signalling. Variable processing of opioid receptor messenger RNAs may lead to the presence of several isoforms of the μ receptor. Each opioid receptor type can function either as a monomer or as part of a homo- or heterodimer or higher multimer. Additionally, recent evidence points to the existence of agonist bias in the signal transduction pathways activated through μ receptors, and to the presence of regulatory allosteric sites on the receptors. This brief review summarizes the recent discoveries that raise challenges for receptor definition and the characterization of signal transduction pathways activated by specific receptor forms.

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This article is part of a themed section on Opioids: New Pathways to Functional Selectivity. To view the other articles in this section visit