Common

• Irritable bowel syndrome, lactase deficiency, parasites, caffeine, alcohol, laxative abuse

Osmotic

• Lactase deficiency
• Medications: antacids, lactulose, sorbitol, Olestra
• Factitious: magnesium-containing antacids or laxatives

Secretory

• Hormonal: Zollinger-Ellison syndrome (gastrinoma), carcinoid, VIPoma, medullary thyroid carcinoma
• Laxative abuse: phenolphthalein, cascara, senna
• Villous adenoma
• Medications

Inflammatory conditions

• Inflammatory bowel disease
• Microscopic colitis (lymphocytic or collagenous)
• Cancer with obstruction and pseudodiarrhea
• Radiation colitis

Malabsorption

• Small bowel: celiac sprue, Whipple's disease, tropical sprue, eosinophilic gastroenteritis, small bowel resection, Crohn's disease
• Lymphatic obstruction: lymphoma, carcinoid, tuberculosis, Mycobacterium avium complex (MAC), Kaposi's sarcoma, sarcoidosis, retroperitoneal fibrosis
• Pancreatic insufficiency: chronic pancreatitis, cystic fibrosis, pancreatic cancer
• Bacterial overgrowth, eg, diabetes
• Reduced bile salts: ileal resection, Crohn's disease, postcholecystectomy

Motility disorders

• Irritable bowel syndrome
• Postsurgical: vagotomy, partial gastrectomy, blind loop with bacterial overgrowth
• Systemic disease: diabetes mellitus, hyperthyroidism, scleroderma
• Caffeine or alcohol use

Chronic infections

• Parasites: giardiasis, amebiasis, strongyloidiasis

Other

• Ischemic colitis
• Adrenal insufficiency

• Acute diarrhea
• Diarrhea in AIDS
• Diarrhea in diabetes
• Fecal incontinence
• Malabsorption
• Intestinal bacterial overgrowth