I'd rather not get led into crack addiction by marijuana smoke or imbibing alcohol. Instead, I can point out that nearly all upper-class adults drink occasionally, and nearly no upper class adults end up with crack addiction.
Just about all middle class adults drink, and crack addiction remains a problem largely focused on the lower class.
Thus, I insist that hard drugs are prevalent in the lower class because of poor public education standards and low property taxes, and all the pressures and influences that come with those, and not alcohol. However, the lower (and middle) class is most likely to consume strong alcohol regularly, resulting in an apparent correlation. However, the two are both caused by the same things: poverty.