A Study to Evaluate Tegoprazan as a Diagnostic Tool for GERD

Inclusion Criteria: * Patients aged 19 to 75 years who have experienced symptoms of acid regurgitation or heartburn at least twice a week starting at least 3 months prior to screening. * Baseline Symptom Assessment Questionnaire score of at least 6 at screening. * 7-Day Symptom Assessment Questionnaire score of at least 4 at randomization. Exclusion Criteria: * Known hypersensitivity to Potassium-Competitive Acid Blockers (P-CABs) or benzimidazoles. * Presence of gastrointestinal warning symptoms (e.g., progressive dysphagia, bleeding, unintentional weight loss within 3 months, hematemesis, anemia, hematochezia, or rectal bleeding) without a confirmed negative tumor finding on endoscopy. * History of or planned gastrointestinal surgery that potentially affects gastric acid secretion. * Diagnosed with Zollinger-Ellison syndrome or other gastric acid secretion disorders. * Endoscopic evidence of esophageal stricture, ulcer stenosis, esophageal varices, Barrett's esophagus (\> 3 cm), eosinophilic esophagitis, gastrointestinal bleeding, active peptic ulcer, or malignant tumor. * Clinically significant hepatic or renal impairment (AST, ALT, ALP, GGT, total bilirubin, and creatinine greater than or equal to 2 times the upper limit of normal \[ULN\]) at Screening. * Use of any prohibited medications within the specified wash-out periods or requiring continuous use during the study: 1. Within 2 weeks prior to screening: Acid suppressants (PPIs, P-CABs). 2. Within 1 week prior to screening: Prokinetics, H2 receptor antagonists, gastric mucosal protectors, antacids, or anticholinergics. 3. During the study period (continuous use): Corticosteroids, NSAIDs, antithrombotics, anticoagulants, antipsychotics, antidepressants, or anxiolytics.