Peptic ulcers are sores in the inner lining of the stomach or upper small intestine. They form when the digestive juices produced by the stomach erode or eat away the lining of the digestive tract. Peptic ulcers may form in the lining of the stomach (gastric ulcers) or just below the stomach, at the start of the small intestine (duodenal ulcers).

The most common causes of peptic ulcers are infection with Helicobacter pylori (H. pylori) bacteria and long-term use of nonsteroidal anti-inflammatory drugs (NSAIDs). NSAIDs include aspirin, ibuprofen (Advil or Motrin), and naproxen (Aleve).