None of those are legal OTC. Alcohol is, although there is an age restriction. Since the availability is restricted, those drugs (and some more than others) have a significant black market associated with it. All because they are restricted. Not to mention saying that drugs like meth and cocaine are legal is rather disingenuous, since both are rarely prescribed.
Meth, one of the amphetamines was once used until a drug very close to it came along, methylphenidate, a.k.a., Ritalin.
Disingenuous? No, not at all since when calls are made for legalization what is really being asked for is societal approval for the users choice of use.
What produces a “black market” is the desire of people who will feed their appetites regardless the cost, to themselves or others.