This study is testing a new treatment called **MHS-1031**, a special type of prebiotic, for people with GERD (Gastroesophageal Reflux Disease), which causes heartburn. GERD happens when stomach acid goes back into the tube connecting your mouth and stomach, causing a burning feeling. The study will see if MHS-1031 can help people who are already using PPIs (Proton Pump Inhibitors), medicines that reduce stomach acid, to have more days without heartburn.

The study is randomized (participants are chosen by chance), double-blind (neither participants nor researchers know who gets the real treatment or a fake one), and placebo-controlled (some people get a fake treatment, called a placebo, for comparison). Participants will answer questions about their heartburn and use of other medicines during the study. This helps researchers know if the new treatment works.

• The study has three parts: a remote 2-week check, an on-site visit, and an 8-week treatment phase.
• Participants must be 18-75 years old, use PPIs daily, and have had GERD symptoms for at least 3 months.
• Participants cannot use certain medicines or have certain health issues, like recent surgery or cancer.