Peptic ulcer disease involves breaks in the mucosal lining of the stomach or duodenum that penetrate through the muscular layer. The most common causes are infection with H. pylori bacteria and use of non-steroidal anti-inflammatory drugs (NSAIDs). Symptoms include abdominal pain, nausea, and weight loss. Diagnosis involves endoscopy to visualize the ulcers. Treatment involves antibiotics to eradicate H. pylori, proton pump inhibitors to reduce acid secretion, and avoidance of NSAIDs. Surgery is reserved for complications or treatment failure.