Meth doesn't actually do the things you see in the propaganda horror pictures with a 'before and after'. Its habits of a negative kind, like picking at skin, if someone does that kind of crap, coke can do it too, amphetamine, methylphenidate, ethylphenidate and any other active stimulant ritalinic acid ester. come to think of it, any psychostimulant of the strongly monoaminergic DA/NA releaser or/and reuptake inhibitor type.
Although with grossly excessive use, stimulants can cause ageing of skin complexion, potentially, due to increased oxidative stress. The candle that is lit with the strongest flame burns the shortest being the principle in that respect. But it doesn't mean candles are necessarily bad. Just that you don't want them in the wrong place at the wrong time (I.e excess, in the case of meth, speed. coke, MDMA or anything else akin to either pure stimulants or stimulant-entactogens). You don't want to go looking for a gas leak with a lit candle, or you're going to get your face roasted off.
For what its worth, I've never seen anything terrible happen to my skin as a result of using any of them. And I've tried a fair variety of different stimulants, from amphetamines, to MDMA, to AMT, to methyl and ethylphenidate (ritalin's ethyl ester counterpart) to coke to the Rolls Royce of psychostimulants, 3-fluorophenmetrazine, a substituted phenylmorpholine. And I don't look like a crack-whore hag that was birthed in a dumpster and will die in a gutter, probably bitten in the throat by a redneck hillbilly hick's one-eyed trouser snake and dying with a face-full of poison.
Although, when things are badly made, and not all clandestine chemists take the same care and due attention to detail and thoroughness that they ought to, that some clandestine chemists do; then the nasty byproducts can be, well, nasty. Just look at the russian 'krokodil' phenomenon. (essentially, as I understand it, using SOCl2 to produce alpha-chlorocodide, then performing a red phosphorus-iodine reduction, and shooting the resulting cocktail of slops, after, presumably filtering out the solid phosphorus residues, and MAYBE doing an acid-base extraction and neutralizing the PH 'to taste' (I.e using tongue as PH paper)
Yeah, its that bad. Result is a horrid cocktail of slop containing a very small amount of desomorphine-D among all sorts of filth, from the point of view of veins and tissues, such as iodinated things, bits of red phos, iodine itself, in solution, nonpolar solvents and near certainly a PH balance that is NOT anything approaching isotonic sterile saline. Although sterile, that I could see as a possibility given that it'd be precious fucking few, if any living organism which could survive in such a mixture of noxious swill.
Its a russian and eastern european phenomenon, primarily made from codeine, using thionyl chloride from batteries, red phosphorus, probably matchbox-scrapings grade garbage when it comes to the phossy, shit I wouldn't even work with in my lab let alone use to make something that I actually would consume. (complete with the likes of the antimony trisulfide also present in there as an impurity, and I highly doubt that the russki peasant addicts to krokodil (the word, in russian, means, not too surprisingly 'crocodile' because of the way it makes people's skin discolor green and start scaling and flaking and then finally falling off, until..shit, don't go looking for the pictures if you haven't a strong stomach. I've seen the most harrowing picture, of a girl, who used the shit, and she literally had her forearm tissue, skin, subcutaneous fat, vasculature, and muscle all, MELTED OFF, down to the exposed full length of the radius and ulna bones. Average lifespan of a krokodil addict, who cook the stuff hit by hit, (lasts a couple of hours so they exist only to stop the addiction withdrawals crucifying them more or less) is between a few months and a year at the longest.
Yet desomorphine-D can be cleanly made, going via alpha-chloromorphide and then using a palladium catalyst on a support, in isopropanol as both solvent and H2 donor as I understand it, without any of that awful slime produced (or the awful slime produced by liquefactive and putrefactive necrosis of tissue until your bones are showing from one side to the other), and worked up to produce a potent and highly sought after in terms of being one of the most euphoric opioids around. It was used as a prescription drug in some of the scandinavian area countries, switzerland or sweden or norway, IIRC, although the last patient scripted it eventually passed away. Without turning into a tortured being who the kindest thing that could be done for them is to grant them a bullet in the head. (making sure to remove the head from its shoulders to ensure that it does not rise again moaning things about recipes for braaiinnssssesss)
So the way things are made can have a very significant bearing on quality, and quality is just that vital. I doubt a medical system would prescribe a drug that inherently caused the most horrendous tissue necrosis I have EVER seen, on a living organism. Something not even maggots would touch. And whilst I'd trust myself to perform the catalytic hydrogenation route, sure, I'd not touch 'krokodil' for ANY sum of money or inducement.