antiacid vs gastric antacid

antiacid and gastric antacid both are nouns.

Word	Noun	Adjective	Verb	Adverb
antiacid	Yes	No	No	No
gastric antacid	Yes	No	No	No

As nouns, antiacid and gastric antacid are synonyms defined as:

antiacid and gastric antacid: an agent that counteracts or neutralizes acidity (especially in the stomach)

Other synonyms of antiacid include alkaliser, alkalizer, antacid.

antiacid (noun)	gastric antacid (noun)
an agent that counteracts or neutralizes acidity (especially in the stomach)	an agent that counteracts or neutralizes acidity (especially in the stomach)