gastric antacid vs antiacid

gastric antacid and antiacid both are nouns.

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

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

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

Other synonyms of gastric antacid include alkaliser, alkalizer, antacid.

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