Etonitazene

Etonitazene is a potent analgesic drug shown to be approximately 1000–1500x the potency of morphine in animal models but only 60x in man. It is one of several benzimidazole opioids, and is structurally related to clonitazene (where the p-ethoxybenzyl group is replaced by a p-chlorobenzyl group; however, clonitazene itself has only 3x the potency of morphine).

Later work discovered that if a carboxide moiety is placed onto the carbon between the benzimidazole and the p-ethoxybenzyl, compounts up to 4x more potent were discovered It is of interest that the extra hydrogen-bond acceptor overlays the nociceptin receptor such as MCOPPB.

It has a strong dependency potential similar to that of morphine, and a strong tendency to produce respiratory depression, and is therefore not used in humans. It is however useful in addiction studies on animals. It is often used in studies requiring the animals to drink or ingest the opiate because it is not as bitter as the opiate salts, i.e., morphine sulfate.