Opioid receptor agonist-antagonists may improve analgesia and safety when co-administered with full mu-opioid agonistsNew Framework Suggests Safer Ways to Manage Opioid Pain

Opioid receptor agonist–antagonists occupy a distinctive position between high-efficacy agonists and pure antagonists and have been widely used in clinical pain management. Nevertheless, their pharmacological complexity and dose-dependent receptor interactions have led to persistent controversy regarding their analgesic efficacy, ceiling effects, and clinical performance when combined with full μ-opioid receptor agonists. Most existing reviews focus on individual agents or isolated mechanisms and do not adequately address the dynamic relationship between receptor selectivity, intrinsic efficacy, and dose–effect behavior that underlies their clinical outcomes. This narrative review integrates recent preclinical and clinical evidence to examine the pharmacological properties and clinical application strategies of opioid receptor agonist–antagonists, with particular emphasis on κ-opioid receptor agonism, μ-opioid receptor partial agonism or antagonism, and their interactions across different dose ranges. We discuss the mechanistic basis of the analgesic ceiling effect observed with μ-partial agonists, highlighting that this phenomenon reflects limited intrinsic efficacy rather than a dose-dependent transition to pure antagonism. Furthermore, the review analyzes how agonist–antagonists may exert synergistic or functional antagonistic effects when co-administered with full μ-opioid agonists, depending on dose, receptor affinity, and binding kinetics. At low to moderate doses, complementary κ–μ receptor modulation may enhance analgesia while attenuating opioid-related adverse effects such as respiratory depression, pruritus, and nausea, whereas excessive dosing may compromise analgesic efficacy or increase sedation. By synthesizing receptor-specific mechanisms with clinical dosing considerations, this review proposes a receptor-selective, dose-dependent framework to support safer and more effective use of opioid receptor agonist–antagonists in contemporary multimodal pain management.