Schedule-induced oral self administration of etonitazene.

Rats were induced to drink either a saline-etonitazene solution or a saline solution with a schedule-induced polydipsia paradigm. When water was freely available, the rats continued to drink the saline solution or the saline-etonitazene solution, rather than the water. When the locations of the solutions were switched, the rats that were drinking saline switched to water (drank at the usual location), but the rats that were drinking saline-etonitazene continued to drink the saline-etonitazene solution (drank from the bottle at the other location). Naloxone administration temporarily eliminated the drinking of saline-etonitazene solution, but not that of saline solution.