antacid vs gastric antacid

antacid and gastric antacid both are nouns.

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

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

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

Other synonyms of antacid include alkaliser, alkalizer, antiacid.

antacid (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)

antacid (adjective)	gastric antacid (adjective)
acting to neutralize acid (especially in the stomach)