over-the-counter drug vs over-the-counter medicine

over-the-counter drug and over-the-counter medicine both are nouns.

Word	Noun	Adjective	Verb	Adverb
over-the-counter drug	Yes	No	No	No
over-the-counter medicine	Yes	No	No	No

As nouns, over-the-counter drug and over-the-counter medicine are synonyms defined as:

over-the-counter drug and over-the-counter medicine: a drug that is sold without a prescription

over-the-counter drug (noun)	over-the-counter medicine (noun)
a drug that is sold without a prescription	a drug that is sold without a prescription