Gastric ulcer. Light micrograph of a section through a stomach with a gastric ulcer, which has perforated (torn) and destroyed the protective membranes (mucosa) lining the stomach. Gastric ulcers are caused by the action of acid, pepsin and bile on the mucosa. If the mucosa is compromised due to excess alcohol consumption, stress or certain drugs,it can be eaten away. Symptoms include vomiting and pain. Most cases clear up with antacid drugs, but if ulcers reoccur or even perforate the stomach, surgery is required.