the shake and bake method uses "sudafed"/pseudoephedrine. therefore, it will produce d meth
> This is definitely true for meth, where almost every method yields racemic meth
not quite true, because the main precursor pseudoephedrine already had the correct stereochemistry in place. you would actually have to do effort to racemize that asymmetric carbon. But it is true that if your precursors are racemates or not asymmetric and you are not using some fancy asymmetric catalysis or tedious resoltuion your product will be racemic. An example of a racemic meth synthesis that does not involve P2P is direct amination of allylbenzene.
Do you know if these are well understood and tracked over time?
I think it's actually the opposite of impurities. The tech and supply chains have gotten so good, the purity had gone way up and the cost down, that people are just using way more of it.
Methamphetamine is very, very stable. It stays as methamphetamine when it's vaporized, regardless of whether we're talking d-meth or l-meth.
> There doesn't seem to be debate that P2P processes create l-meth and d-meth, and that l-meth was less common in earlier versions.
Not quite. p2p done naively creates racemic meth, yes, but the modern methods, which have been used for years, purify that to enantiopure d-methamphetamine. They do this by bubbling d-tartaric acid through the racemic mixture, which separates the two enantiomers thus yielding the desired pure d-meth.
Furthermore, historically racemic meth was much more common. AFAIK the infamous "shake and bake" technique creates racemic meth. I do know that there is a pseudofed route that yields d-meth, but I think it's different than shake and bake. So don't quote me on this paragraph, but at a minimum we know that in the last several years, almost all meth seized in the US is highly pure/potent d-methamphetamine. There is less l-meth than ever.
> I just don't think the evidence is so weak that we can discard the potential that l-meth is involved.
On the contrary, the evidence is so weak that we literally can discard that l-meth is involved. First of all l-meth is better studied than you say. I would bet to approve the l-methamphetamine-based vics vapo inhaler they had to at least do animal models with large amounts of pure l-meth.
Second of all, and this is what blows the giant hole in your argument, there is no surge of l-meth. There is less l-meth than there has ever been in the history of methamphetamine.
Thirdly - this ties into the second point - you seem to thikn that getting racemic methamphetamine is something particular to the p2p method. It's not. As a general rule, synthesis of any compound yields the racemic version (if we're talking a compound with two enantiomers). This is definitely true for meth, where almost every method yields racemic meth. AFAIK there's a pseudoephedrine route that yields straight d-meth, but like I mentioned above the current state of the art is just to do a big p2p synth route and then separate out the d enantiomer specifically.