Secretory diarrhea occurs when the small and large bowel secrete more electrolytes and water than they absorb. Secretagogues include bacterial toxins (eg, in cholera), enteropathogenic viruses, bile acids (eg, after ileal resection), unabsorbed dietary fat (eg, in steatorrhea), some drugs (eg, anthraquinone cathartics, castor oil, prostaglandins), and peptide hormones (eg, vasoactive intestinal peptide produced by pancreatic tumors). Microscopic colitis (collagenous or lymphocytic colitis) causes 5% of secretory diarrhea. It is 10 times more common in women, generally affecting persons >= 60. Nausea, vomiting, abdominal pain, flatulence, and weight loss may occur, although the diarrhea is often without other symptoms. Symptoms are often prolonged. Loperamide can be used to control symptoms, and histologic changes may resolve with prednisone or sulfasalazine.