N-Desethyl isotonitazene is of particular concern, as it may combine high MOR binding affinity and functional potency (Walton et al. 2023; Vandeputte et al. 2023; Kozell et al. 2024) with prolonged respiratory depression in vivo (Malcolm et al. 2023). Here, OPRM1 is linked to Respiratory insufficiency due to muscle weakness.