One would also expect to find at least an innate (i.e. not brought on directly by the drug but e.g. by the anticipation to it) dopamine reaction to opioid administration in opioid addicts. Alas, when a single is found in animal models (and It is really fewer than for psychostimulants), https://marioodreq.mysticwiki.com/2071609/the_ultimate_guide_to_ketamin_depression