Gastric ulcer. Gastroscope (endoscope) view of a gastric ulcer (white, upper left) on the lining of the stomach. Also known as a peptic ulcer, it forms when digestive juices in the stomach attack the stomach walls. This is usually due to reduced production of the protective mucus which lines the walls. This can be caused by foods and chemicals which irritate the stomach lining, such as alcohol, caffeine and aspirin, or by bacteria. Treatment is with antacid drugs, which reduce the acidity of the stomach's juices, or ulcer-healing drugs such as cimetidine.