GAST and gastroesophageal reflux disease: To solve this issue, as an ideal study design, gastric acid secretion capacity (s-gastrin and p-CgA), gastric acid secretion (pH in the stomach), and acid reflux in the esophagus (pH in the esophagus) should be measured before PPI treatment, at the end of treatment (e.g., week 4), at an early (e.g., week 5) timepoint post withdrawal, at a middle (e.g., week 6) timepoint, and at a late (e.g., week 8) timepoint to correlate the change in those three factors.