OPRM1 and respiratory depression: OL-CTOP significantly prevented morphine-induced respiratory depression after pretreatment with 100 μg († p = 0.05 at 20–40 min and p = 0.02 at 40–60 min; Tukey’s test, Figure 6) or 600 μg († p ≤ 0.009, 0–60 min; Tukey’s test, Figure 6), consistent with a dose-dependent MOR antagonism.