drug abuse vs substance abuse

drug abuse and substance abuse both are nouns.

Word	Noun	Adjective	Verb	Adverb
drug abuse	Yes	No	No	No
substance abuse	Yes	No	No	No

As nouns, drug abuse and substance abuse are synonyms defined as:

Other synonyms of drug abuse include habit.

drug abuse (noun)	substance abuse (noun)
excessive use of drugs	excessive use of drugs