Apeptic ulcer is an open sore or hole that develops inside the lining of the stomach, esophagus, and the upper part of the small intestine (also known as the duodenum). It may be caused by a bacterial infection such as H. pylori, stomach acids, or even from taking non-steroidal anti-inflammatory drugs. A peptic ulcer may also be known as a duodenal ulcer, a gastric ulcer, or a stomach (gastric) ulcer. It is estimated that about 1 in every 50 people in the United States have peptic ulcers.