Bleeding stomach ulcer. Gastroscope (endoscope) view of a bleeding gastric (peptic) ulcer of a 71 year-old male patient. The bleeding was controlled by using an probe, which passes an electric current through the bleeding vessel to seal it (electrocautery). Ulcers are caused by excessive stomach acid (digestive juice). This acid, often combined with excess alcohol and caffeine, attacks the stomach wall, causing pain and discomfort. If the wall's protective mucus becomes thinned, possibly due to mental stress or bacterial attack, the acid can perforate the stomach wall. A perforated ulcer can result in anaemia and vomiting blood (haematemesis).