PZM21 is an effective and selective μ opioid receptor agonist (EC50: 1.8 nM).

μ opioid receptor:1.8 nM (EC50)

At hERG, PZM21 has an IC50 of between 2 and 4 μM, 500- to 1,000-fold weaker than its potency as a μOR agonist. Signalling by PZM21 and other μOR agonists appears to be mediated primarily by the heterotrimeric G protein Gi/o, as its effect on cAMP levels is eliminated by pertussis toxin and no activity is observed in a calcium release assay [1].

PZM21 is a highly selective μOR activator with significant Gi activation and minimal activation of β-arrestin-2, differentiating it from morphine by demonstrating greater efficacy in the affective aspect of pain relief compared to the reflexive aspect, without causing respiratory depression or exhibiting morphine-like addictive qualities in mice at equivalent analgesic doses. In a mouse hotplate assay, PZM21 achieved a maximal effect of 87% for pain relief 15 minutes post-administration of the highest dose [1]. Furthermore, PZM21 exerts a durable analgesic effect on central nervous system (CNS)-mediated pain without the typical opioid-induced side effects of respiratory depression and constipation [2].