Just one would also expect to find at the least an innate (i.e. not brought on directly via the drug but e.g. via the anticipation to it) dopamine reaction to opioid administration in opioid addicts. Alas, when one is found in animal designs (and it's under for psychostimulants), in vivo https://ricardocsixl.yourkwikimage.com/2118951/phenyl_2_nitropropene_an_overview