An ulcer is a break in the lining of the gut and most commonly occurs in the first part of the small intestine where it joins the stomach (called the duodenum). The most common cause of duodenal ulceration nowadays is treatment with anti-inflammatory drugs such as ibuprofen or aspirin. Another common cause is infection with a bacterium called Helicobacter pylori. It appears that the drugs and the infection may create more damage together than either agent alone (called synergism). Most people with a duodenal ulcer experience upper abdominal pain and sometimes nausea or vomiting. An upper gi endoscopy will be able determine the extent of ulceration.