Antacids are crucial in the treatment of gastro-esophageal reflux disease and peptic ulcers. Antacids based on the calcite phase of bulk calcium carbonate have been the standard for over fifty years. More recent research has shown that nanomaterial forms of such bulk materials often have improved properties. However, the metastable vaterite form of calcium carbonate is particularly difficult to synthesize as a nanomaterial, and thus has not been extensively studied. Here, we describe the synthesis of these particles and investigate them for antacid applications. Experimental and computational approaches show that nanoscale vaterite particles maintain neutral gastric pH values three times longer than commercial antacids.