Inclusion Criteria:

• Adult patients (men and women, ages 18-75 inclusive) with symptoms of dyspepsia thought to represent FD (Rome IV criteria; 5, https://theromefoundation.org/rome-iv/rome-iv-criteria/).
• Patients will be identified as direct referrals to the general GI clinic, the general medical clinic, or the motility clinic. Referring providers will also be notified of active research trials in the Division of Gastroenterology, and this study will be highlighted.
• During initial evaluation, patients’ symptoms will be assessed, and patients categorized into either the PDS, EPS or mixed subtype of FD.  

Exclusion Criteria:

• Symptoms are thought to represent an organic disorder (e.g., peptic ulcer disease, hepatitis, pancreatitis, inflammatory bowel disease, type I diabetes, a known malignancy, radiation-induced injury, an active infection, vasculitis, celiac disease), or if the patients have known esophagitis, eosinophilic esophagitis or H. pylori. 
• Patients with prior surgery to the esophagus, stomach or duodenum will be excluded, as will those taking proton pump inhibitors (PPIs), opioids, corticosteroids and those taking regular (daily) antihistamines, non-steroidal anti-inflammatory drugs (NSAIDs), or mast-cell stabilizing agents within the prior 2 weeks.  Of note, patients taking PPIs will be given the opportunity to discontinue their PPI in favor of famotidine 20 mg daily for 2 weeks before enrollment. 
• Patients with known allergies to lactulose: mannitol.
• Active tobacco use and excessive alcohol use (defined as 8 or more drinks per week for women or 15 or more drinks per week for men; http://ww.cdc.gov).
• Co-existing IBS will be allowed to enter the study as long as symptoms are not predominant.
• Hepatic and renal impairment within the past 3 months.
  • AST/ALT > 2X ULN;
  • Total Bilirubin > 2 X ULN;
  • Estimated Glomerular Filtration Rate (eGFR) of < 60 mL/min/BSA.
• Diagnosed with galactosemia.
• Pregnant or breastfeeding women.
• Patients with documented or reported lactose intolerance.

Eligibility last updated 6/6/23. Questions regarding updates should be directed to the study team contact.