Etonitazene: an opioid selective for the mu receptor types.

Specific radioligand binding protocols were utilized to compare the affinity of morphine and the high-potency opioid etonitazene at mu 1, mu 2, delta, kappa 1 and sigma receptors. Both etonitazene and morphine displayed a mu 1-selective binding profile; however, etonitazene had a 2500-fold higher affinity at this receptor type. The latter result is consistent with the relative potencies or morphine and etonitazene in various behavioral tests.