Acid reduction remains the most common treatment prescribed empirically by pediatric gastroenterologists for children with functional dyspepsia (FD). When acid reduction therapy fails to provide patients with a therapeutic effect, ketotifen and cromolyn, mast cell stabilizers, represent an attractive potential therapy given data implicating mast cells in the generation of dyspeptic symptoms. Although there have been no adult or pediatric studies on the use of mast cell stabilizers in patients with FD, benefit has been demonstrated in adults with IBS and children with eosinophilic gastroenteritis. Additionally, previous studies show mucosal eosinophilia is highly correlated with functional dyspepsia. Our usual current treatment pathway for functional dyspepsia in association with duodenal mucosal eosinophilia is as follows: acid-reducing medication/montelukast → addition of H1 antagonist → addition of budesonide → addition of oral cromolyn. If ketotifen is effective, it offers the advantage of being able to replace both the H1 antagonist and the oral cromolyn at a substantially reduced cost (approximately 10% of the cost of cromolyn alone). This study aims to introduce ketotifen earlier in the treatment pathway to examine its efficacy on children with functional dyspepsia in association with duodenal eosinophilia.