A gastric ulcer (GU) is an open sore in the lining of the stomach, where acid and pepsin have eaten through the protective mucus barrier into the tissue beneath. The great majority are caused by infection with Helicobacter pylori bacteria or by long-term use of non-steroidal anti-inflammatory drugs (NSAIDs) such as ibuprofen, which weaken mucosal defences. Typical symptoms are gnawing upper-abdominal pain, often worse when the stomach is empty, plus nausea and loss of appetite; complications include bleeding, perforation, and obstruction. Diagnosis is by endoscopy with biopsy, and treatment targets the cause — antibiotics to eradicate H. pylori, stopping NSAIDs where possible, and acid-suppressing drugs to let the ulcer heal.