Methods and compositions are disclosed utilizing hydroxylansoprazole for the treatment of ulcers in humans. Hydroxylansoprazole exhibits a lessened liability toward drug-drug interactions than lansoprazole and a more predictable dosing regimen than lansoprazole. Hydroxylansoprazole is also useful for the treatment of gastroesophageal reflux and other conditions related to gastric hypersecretion such as Zollinger-Ellison Syndrome.