Any home meth lab chemist knows that Vicks Vapor Inhalers used to serve (it seems they've altered the formula) as a pretty good precursor for ice, speed, crystal, crank or whatever you want to call it. There's a good reason for this.
If you check the back of the package, it lists the active ingredient in these inhalers as l-desoxyephedrine. Not-so-coincidentally, Desoxyn is the brand name for pharmaceutical methamphetamine, which used to be prescribed for extremely severe cases of ADD, although I believe now manufacturing has been discontinued.
l-desoxyephedrine used to be labeled as levmetamfetamine. While I'm not sure about the reasons behind the obfuscation, any amateur chemist can tell you that this is indeed N-methyl-alpha-methyl-phenethylamine, or methamphetamine.
Methamphetamine, like many organic compounds, comes in two stereoisomers, effectively mirror images of each other. These would be levo-methamphetamine (l-methamphetamine) and dextro-methamphetamine (d-methamphetamine).
The levo isomer has, it seems, almost exclusively peripheral sympathomimetic effects, like those of Sudafed (pseudoephedrine or phenylephrine if it's Sudafed PE). A sympathomimetic, so called because it mimics the effects of the sympathetic nervous system, activated in situations of stress, can, among other things, cause blood vessels to constrict, producing a decongestant action.
The dextro isomer, on the other hand, is also active in the central nervous system, producing euphoria and addiction. Few meth manufacturers would try to pass off l-methamphetamine as d-methamphetamine.
Interestingly enough, if you inhale enough Vicks and take a drug test, you'll likely turn up positive for methamphetamine. Most tests do not distinguish between the two isomers, although if you claim it was the Vicks, they'll likely re-test you with a more selective method that will.