A 22-year-old woman presents with chronic diarrhea. She has no abdominal discomfort, feels well, and reports no weight loss or systemic symptoms. Physical examination reveals a healthy young woman who is 5'7" tall and weighs 170 lb. The complete physical examination is normal. Which of the following is the most likely cause of a secretory diarrhea in this young woman?
surreptitious use of stimulant laxatives carcinoid tumor ulcerative colitis lactose deficiency