Home › CFR › Title 21 › Part 33121 CFR Part 331 — Antacid Products for Over-the-Counter (OTC) Human UseSubpart A — General Provisions§ 331.1— Scope.Subpart B — Active Ingredients§ 331.10— Antacid active ingredients.§ 331.11— Listing of specific active ingredients.§ 331.15— Combination with nonantacid active ingredients.Subpart C — Testing Procedures§ 331.20— Determination of percent contribution of active ingredients.§ 331.21— Test modifications.Subpart D — Labeling§ 331.30— Labeling of antacid products.§ 331.80— Professional labeling.