If is is has not been done yet, to confirm that hypothesis (the Drug match the opioid receptor), you will need to compare in 3D the agonist and receptor, first, because its almost free (your time), and at last try it (costly). There should be some better software than others (free and not free), to do so, but by comparing only the suspicious part by their ARN or amino sequence, you could find some clues.
Once built, those molecule, cannot be modify easily (if they can), so you will need to build an amino-acid sequence, that will be encode by ribosomes, by the well known process (i think).
Heroin trig some neuroreceptors (at least one because its really a drug), experimental data could be achieved by different ways, but one could be to scan the brain of a mouse that is trigged, by your protein. Mouse life, could be save by the use of synthetic amplifier system, that will copy the chain of reaction of the nervous cell to achieve a delta color or something easy to see, but I am alone wanting to save mouse life
Maybe you need to be more specific, I will be please to help you more if needed...