Synonyms for Antacid (same or very similar meaning)
WordNet sense 1 (an agent that counteracts or neutralizes acidity (especially in the stomach)):
alkaliser, alkalizer, antiacid, gastric antacidWordNet sense 2 (used especially of drugs or muscles that counteract or neutralize each other's effect):
antagonistic, incompatibleFrom the ODE community, based on WordNetadd/edit