An opioid efficacy switch for reversible optical control of analgesia

Azo-morphine-3 (AM-3) is a photoswitchable ligand that toggles between low and high efficacy states to control mu-opioid receptor activity in vitro and in vivo both in the brain and periphery. AM-3 provides a powerful tool to probe the structural basis of opioid efficacy and enables spatiotemporally precise control of analgesia across pain models with reduced side effects compared with systemic drugs.