This is a multicenter, randomized, double-blind, placebo-controlled, parallel-group study conducted in the United States (US) to assess the efficacy of RP-G28 compared to placebo on symptom reduction related to lactose intolerance.

Inclusion Criteria:

• Patient is 18-75 years of age, inclusive, at screening;
• Intolerance to milk and other dairy products;
• Patient agrees to refrain from all other treatments and products used for lactose intolerance, to follow diet modifications required during periods of the study that include abstinence from all dairy in some periods and consuming dairy in other periods;
• Patient meets the defined minimum lactose intolerance symptom composite score; and
• Patient has positive Hydrogen Breath Test (HBT) results for lactase deficiency.

Exclusion Criteria:

• Patient has a disorder associated with abnormal gastrointestinal motility such as gastroparesis (from any cause), amyloidosis, neuromuscular diseases (including Parkinson's disease), collagen vascular diseases, uremia, or malnutrition;
• Patient has undergone bowel preparation for endoscopic or radiologic investigation within 4 weeks of Screening (example, colonoscopy preparation);
• Patient has a history of surgery that alters the normal function of the gastrointestinal tract including, but not limited to: fundoplication, gastrointestinal bypass surgery, bariatric surgery, gastric banding, colostomy, vagotomy, pyloroplasty, colectomy or other surgery for Crohn's disease or ulcerative colitis; and
• Patient has received antibiotic treatment, or had a high colonic enema, colonic irrigation, colonic hydrotherapy, or colonic cleaning within 30 days prior to or during Screening.