drug user vs doer

drug user and doer both are nouns.

Word	Noun	Adjective	Verb	Adverb
drug user	Yes	No	No	No
doer	Yes	No	No	No

As nouns, doer is a hypernym of drug user; that is, doer is a word with a broader meaning than drug user:

Other hypernyms of drug user include actor, worker.

drug user (noun)	doer (noun)
a person who takes drugs	a person who acts and gets things done