Health Questions and Answers

Question: What causes osmotic diarrhea?


Osmotic diarrhea is caused by ingestion of excessive amounts of a poorly absorbable but osmotically active solute. Commonly implicated substances include mannitol or sorbitol (seen in patients chewing large quantities of sugar-free gum), magnesium sulfate (Epsom salt), and some magnesium-containing antacids. Carbohydrate malabsorption also may cause osmotic diarrhea through the action of unabsorbed sugars (lactulose). Clinically, osmotic diarrhea stops when the patient fasts (or stops ingesting the poorly absorbable solute).

Reference:  Sleisenger MH, Fordtran JS (eds): Gastrointestinal Disease: Pathophysiology, Diagnosis, and Management, 7th ed. Philadelphia, W.B. Saunders, 2003

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