Green’s Dictionary of Slang

fiend n.

1. [late 19C+] (orig. US drugs) an addict, esp. of opium; usu. in comb. with drug name [contemporary use tends to be ironic].

2. [late 19C–1910s] (US campus) a fool [fig. use of sense 1].

3. [late 19C+] an addict, an obsessive, other than of drugs.

4. on bad = good model.

(a) [1900s] (US campus) a clever student.

(b) [1960s] (US black) a general term of praise for any person or thing.

5. [2000s] someone who smokes marijuana alone (since smoking is usu. a communal experience).

In phrases

hoosier fiend (n.) [hoosier n. (5)]

[1930s–50s] (US drugs) an inexperienced or naïve drug user, one who is in the early days of their addiction to narcotics.