Acid peptic disease (APD) refers to a group of conditions involving excessive acid production and damage to the stomach and duodenum lining. It includes gastritis, peptic ulcer disease, and gastroesophageal reflux disease (GERD). Symptoms often include abdominal pain, bloating, heartburn, and nausea. Treatment typically involves lifestyle changes, medications to reduce acid production and heal the mucosa, and antibiotics if an H. pylori infection is present.