Sekio, while I agree totally about set and setting, I have to call bullshit on the statement that it makes no difference what isomers are present. 100% laevo-meth is even OTC in the US (or at least it was, don't know if it still is), isn't it?
If I were to acclimatize you, knowingly, taking breaks to exclude tolerance and neurotransmitter depletion to equal doses by weight of unadulterated D-meth, to L-meth and to the 50-50 racemate, and after you had been thoroughly familiarized with the effects of each, and then I were to give you a double-blind few doses, again separated in time to exclude tolerance and neurotransmitter depletion, that you would be unable, whilst in the same spatial area, and in as similar a mindset as possible, to discriminate between them? I'd bet money that at the very least you'd be able to discriminate between D- and L-meth, and I'd be pretty sure that you'd be able to tell the racemate apart (and thats when it had been thoroughly recrystallized and solvent-washed to remove any trace of the phenylacetone I'd have used to prepare the racemic meth, if this experiment were carried out IRL so you'd be unable to tell it apart by means of the odour of P2P, as delightful as it is, it'd still be a giveaway if left in there)
But for the sake of theorizing, just assume that each of the three were given in equal weight, and that I had made it myself, so as to guarantee it were to be uncut, and after repeated trituration of the HCl salt under dichloromethane or chloroform, carbon tet, etc. etc. to remove the traces of P2P, purified to pharmaceutical grade.
Hell, just compare the transporter affinities for D- and L-meth for NET, DAT, VMAT and perhaps affinity and efficacy at TAAR1. Radioligands are not susceptible to the placebo effect as far as I know, they don't decide 'hey, I'm going to decay at twice my usual rate because I'm in a shitty mood and the dog just crapped all over my lawn'