Zollinger-Ellison syndrome is a rare condition in which one or more tumors form in your pancreas or the upper part of your small intestine (duodenum). These tumors, called gastrinomas, secrete large amounts of the hormone gastrin, which causes your stomach to produce too much acid. The excess acid then leads to peptic ulcers, as well as to diarrhea and other symptoms.
Zollinger-Ellison syndrome (ZES) is rare. The disease may occur at any time in life, but people usually find out they're affected between ages 20 and 50. Medications to reduce stomach acid and heal the ulcers are the usual treatment for Zollinger-Ellison syndrome.