A Study to Evaluate the Efficacy and Safety of Vonoprazan Compared to Placebo in Participants With Symptomatic Non-Erosive Gastroesophageal Reflux Disease

Inclusion Criteria for Run-In Period

• The participant is ≥18 years of age at the time of informed consent signing.
• In the opinion of the investigator or sub investigators, the participant is capable of understanding and complying with protocol requirements.
• The participant signs and dates a written informed consent form (ICF) and any required privacy authorization prior to the initiation of any study procedures. The participant is informed of the full nature and purpose of the study, including possible risks and side effects. The participant has the ability to cooperate with the investigator. Ample time and opportunity should be given to read and understand verbal and/or written instructions.
• The participant identified their main symptom as heartburn, a burning sensation in the retrosternal area (behind the breastbone).
• History of episodes of heartburn for 6 months or longer prior to screening.
• Heartburn reported on 4 or more days during any 7 consecutive days in the Screening Period as recorded in the electronic diary.
• A female participant of childbearing potential who is or may be sexually active with a non sterilized male partner agrees to routinely use adequate contraception from the signing of informed consent until 4 weeks after the last dose of study drug.

Inclusion Criteria for On-Demand Treatment Period

• The participant completes the Run-In Period, during which the participant was at least 80% compliant with open-label study drug.
• The participant has stable disease, ie, no heartburn the last 7 days of the Run-In Period.
• The participant continues to fulfill all eligibility criteria for the Run-In Period (except Inclusion Criteria 4).
• Participant completes at least 80% of diary entries during Run-In Period, including 80% of diary entries over the last 7 days.

Exclusion Criteria for Run-In Period

• Endoscopically confirmed erosive esophagitis (EE) during the Screening Period assessed by the investigator. Endoscopy should be performed after participants meet Inclusion Criteria 6. Any endoscopic confirmation performed in a routine clinical setting within 7 days before signing the informed consent is acceptable to use for the purpose of fulfilling the screening requirement.
• The participant has active irritable bowel syndrome (IBS) or had a flare of IBS requiring therapy within the prior 6 months.
• The participant has a history of or is suspected of having functional heartburn diagnosed by the Rome IV criteria.
• The participant has a history of or is suspected of having functional dyspepsia diagnosed by the Rome IV criteria.
• The participant has endoscopic Barrett's esophagus (>1 cm of columnar-lined esophagus) and/or definite dysplastic changes in the esophagus.
• The participant has any other clinically significant condition affecting the esophagus, including eosinophilic esophagitis; esophageal varices; viral or fungal infection; esophageal stricture; a history of radiation therapy, radiofrequency ablation, endoscopic mucosal resection, or cryotherapy to the esophagus; or any history of caustic or physiochemical trauma (including sclerotherapy or esophageal variceal band ligation). However, participants diagnosed with Schatzki's ring (mucosal tissue ring around lower esophageal sphincter) or hiatal hernia are eligible to participate.
• The participant has scleroderma (systemic sclerosis).
• The participant has a history of surgery or endoscopic treatment affecting gastroesophageal reflux, including fundoplication and dilation for esophageal stricture (except Schatzki's ring) or a history of gastric or duodenal surgery (except endoscopic removal of benign polyps).
• The participant has an active gastric or duodenal ulcer within 4 weeks before the first dose of study drug.
• Use of prescription or non-prescription proton pump inhibitors (PPIs) or histamine-2 receptor antagonists (H2RAs) throughout the study.
• The participant has received vonoprazan in a clinical trial a