Lansoprazole Delayed-Release Capsules 15 mg is a Proton Pump Inhibitor (PPI). PPIs deactivate the pumps in the stomach lining from producing acid, significantly inhibiting acid production (and its overproduction) at the source. PPIs are available over-the-counter or as a prescription to treat ulcers, gastroesophageal reflux disease (GERD) and erosive esophagitis.