The main problem is that this is a really, really subjective thing that we are talking about here. Opioids are depressants, so feelings of "stimulation" are most likely referring to a psychosomatic side effect as opposed to the nervous system actually being stimulated.
I'm not really sure about this thread because the objective is not finite and cant really be explained in data/numbers. Being that this is an HR dedicated forum, I'm just unsure that its valid. We aren't really inquiring about safety or anything.
I'm going to move this to Drug Culture. I think that this type of subjective discussion will be better suited to it.