The mu opioid receptor (MOR) is a G protein-coupled receptor(GPCR)and is responsible for the effects of all medically used opioids.Most opioids activate all inhibitory Gαi/o/z proteins throughMOR, initiating signaling events that culminate in a variety of physiologicaleffects such as analgesia, euphoria, and respiratory depression. Here, OPRM1 is linked to respiratory depression.