Intestinal ulcer. Gross specimen of an ulcer (centre) in the caecum, the point at which the small intestine becomes the large intestine. This ulcer was caused by drugs. The drugs that most commonly cause ulcers are non-steroidal anti- inflammatory drugs (NSAIDs), including ibuprofen and aspirin. These drugs work by inhibiting prostaglandins, which promote inflammation and pain, but also protect the lining of the intestines from the damaging effects of gastric acid. If left untreated intestinal ulcers can lead to bleeding and perforation.