This study is meant to assess the effect of IW-3718 as an added treatment to ongoing once-daily protocol pump inhibitor (PPI) treatment for patients who continue to experience symptoms of their gastroesophageal reflux disease (GERD).

Inclusion Criteria:

• Patient is between 18 and 65 years of age at the Screening Visit; females must not be pregnant or must not be breastfeeding;
• Patient has a confirmed diagnosis of gastroesophageal reflux disease, must be currently taking a proton pump inhibitor (PPI), and must be experiencing GERD symptoms as specified by the protocol.

Exclusion Criteria:

• Patient may not meet any of the excluded conditions specified in the protocol;
• Patient is experiencing alarm symptoms such as GI bleeding, anemia, vomiting, dysphagia, or unexpected weight loss;
• Patient has a clinically significant hypersensitivity or allergies to any of the active ingredients or excipients in the study medication.