substance abuse vs drug abuse

substance abuse and drug abuse both are nouns.

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

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

Other synonyms of substance abuse include habit.

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