Nubain if a very weak opiate. The reason that it's not scheduled is that it is an opiate agonist/antagonist. Stronger opiates like morphine are strictly agonists. Basically that means that Nubain has what is referred to as the "ceiling effect" where at a certain dose the drug begins to block its mechanism of action, effectively shutting itself off.
However, even thought this particular opiate one of the weakest, it still has addiction potential. It's kindoff like saying that a certain ferrari is slow because all the other ones are faster. In other words, it's the weakest of the strongest... Because of this ceiling effect, the majority of users will graduate to stronger opiates (a kind of "gateway" opiate), and it is a steep road downhill from there.
Nobody should touch this drug as it has no real benefits in bodybuilding other than maybe masking pain for a workout, which will only do much more harm than good in the long run. Bodybuilders tend to have the potential for addiction at a considerably higher rate than the average population, it is one of things that helps us succeed in this sport. That is why there is no need to test the waters with this stuff, because once you are in, there is no getting out.