The purpose of this study is to assess the safety and efficacy of lansoprazole microgranules oral suspension, once daily (QD), in infants with gastroesophageal reflux symptoms during a 4-week treatment period.

This study will be conducted by approximately 20 investigative sites in the U.S. and Poland. Participants who qualify will be randomized in equal proportions to receive either lansoprazole Pediatric Suspension (0.2-0.3 mg/kg/day in infants <10 weeks of age or 1.0-1.5 mg/kg/day in infants >10 weeks of age) or Placebo. This study consists of three periods: Pretreatment Period of 7-14 days, Double-Blind Treatment Period of 4 weeks (Dosing), and the Post-Treatment Period of 30 days (Follow-Up).

Inclusion Criteria:

• At least 7 days post-surgery at the time of Screening (Study Visit 1) with no anticipated need for surgery during the study.
• Experiencing symptoms of gastroesophageal reflux disease (regurgitation, vomiting or "spitting up," fussing/irritability, feeding refusal, crying during feeding, arching back, poor weight gain, or extraesophageal manifestations) or endoscopy proven reflux disease.
• Must continue to have reflux symptoms during the Pretreatment Period despite reducing or eliminating exposure to tobacco smoke, using one positioning and feeding strategy the last 7 days as documented in the Daily Diary.
• The infant exhibited crying, fussing, or irritability during or within 1 hour of feeding in >25% of all feedings during the last 4 days of the Pretreatment Period as documented in the Daily Diary.

Exclusion Criteria:

• Body weight <2.0 kilogram at Dosing Day 1 of the Double-Blind Treatment Period.
• Unstable, congenital or acquired, clinically significant disease of any major organ system (cardiovascular, respiratory, renal, hepatic, metabolic, etc.), including suspected and/or documented culture-proven sepsis.
• Coexisting esophageal disease (e.g., eosinophilic esophagitis, viral, bacterial or fungal infection) or caustic or physiochemical trauma to the esophagus.
• Any congenital anomaly of the upper gastric intestinal tract that might interfere with gastrointestinal motility, pH, absorption, or active or known history of necrotizing enterocolitis that has been surgically corrected.
• Use of a proton pump inhibitor within 30 days prior to Dosing Day 1.
• Use of H2 Blockers (i.e. Zantac) within 7 days prior to Dosing Day 1.
• Allergy to proton pump inhibitors (i.e. Prilosec, Prevacid).
• Use of prokinetics (e.g., metoclopramide) unless on a stable dose for at least 3 days prior to entering the Pretreatment Period.
• Unable to obtain stable drug levels after continuous treatment with required drugs including theophylline derivatives, digoxin, phenytoin, phenobarbital, or carbamazepine within the 7 days prior to Dosing Day 1.
• Clinically Significant abnormalities in clinical laboratory values.