Purpose of review:The purpose of this article is to describe the molecular characteristics and currently conceived mechanisms in the functioning of opioid receptors, opioid drugs are of great interest in the analgesic management of patients with oncologic and nononcologic pathologies.Recent findings: Opioid receptors are not considered to act as single units, producing a particular effect with their stimulation.They are now perceived as functional assemblies with the possibility of having heterodimeric activation as well as having allosteric characteristics that will modify the response mechanisms.On the other hand, activations of other types of receptors involved in nociception have been determined with the chronic use of drugs acting on opioid receptors.Summary: Endogenous opioid receptors are a group of four receptors that can modify the descending nociceptive pathways modulating pain but that can also activate other types of receptors involved in nociception.Additionally, they are receptors that can be activated jointly or partially and generate different types of responses and side effects.