The term "junkie" derives from addicts who stole junk metal to support their habit.
Um.... do you have a cite for that? While I don't have a cite, I'm quite sure that the term "junk" comes from users not being able to kick their habit. As in: "I know I should pay my rent, but instead I'll fill my veins with this junk." (Junk meaning trash, crap, garbage, etc... like junk food)
i always thought it was strictly related to heroin being called "junk"
That is what I was referring to; sorry if I wasn't clear. "Junkie" comes from heroin being called "junk". Heroin is called "junk" because the users considered it to be junk/trash. However, they continued to use the "junk", so they became "junkies". I highly doubt that it was called junk because they sold junk metal to support their habit.
The prohibition of recreational drugs after 1914 quickly turned hundreds of thousands of solid citizens into criminals. Hundreds of physicians became jailbirds. Black-market merchants demanded piles of cash for what used to be a few pennies worth of powder from the friendly local apothecary.
"The scope of this change," writes Courtwright, "can be described by the etymology of a single word, 'junkie.' During the early 1920s, a number of New York City addicts supported themselves by picking through industrial dumps for scraps of copper, lead, zinc and iron, which they collected in a wagon and then sold to a dealer. Junkie, in its original sense, literally meant junkman.
From Online Etymology Dictionary:
Junkie "drug addict" is attested from 1923, but junk for "narcotic" is older.