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Upon completion of the chapter, the reader will be able to:

  1. Identify the causes of constipation.

  2. Compare the features of constipation with those of irritable bowel syndrome with constipation (IBS-C).

  3. Recommend lifestyle modifications and pharmacotherapy for treatment of constipation.

  4. Distinguish between acute and chronic diarrhea.

  5. Compare diarrhea caused by different infectious agents.

  6. Explain how medication use can cause diarrhea.

  7. Discuss nonpharmacologic strategies for treating diarrhea.

  8. Identify the signs and symptoms of IBS.

  9. Contrast IBS with diarrhea (IBS-D) and IBS-C.

  10. Establish treatment goals for IBS.

  11. Evaluate the effectiveness of pharmacotherapy for IBS.


Constipation and diarrhea are common gastrointestinal (GI) complaints that have various etiologies. Thorough patient assessment is important to accurately identify the underlying cause and implement safe and effective treatment. Functional gastrointestinal disorders (FGIDs) have received increasing attention in recent years.1 FGIDs are characterized by persistent and recurring GI symptoms due to abnormal GI tract function but without structural or biochemical abnormalities. As a result, many diagnostic tests (eg, x-rays, endoscopic examinations) are often negative. The most common FGID is irritable bowel syndrome (IBS). This chapter will focus on the evaluation and management of constipation, diarrhea, and IBS.


image Constipation, when not associated with symptoms of IBS, is a syndrome characterized by infrequent bowel movements (< 3 stools per week) or difficult passage of stools, hard stools, or a feeling of incomplete evacuation. Occasional constipation usually does not require medical evaluation or treatment.


Constipation affects people of all ages and occurs in approximately 16% of all adults and in one-third of adults age 60 and older. Although it is rarely life threatening, constipation results in over 8 million physician visits, 1.1 million hospitalizations, and 5.3 million prescriptions annually. In 2016, US sales of nonprescription laxative products totaled more than $1.3 billion.2

Constipation can be due to primary and secondary causes (Table 21–1). Functional constipation is defined as constantly problematic, infrequent, or seemingly incomplete defecation that does not meet criteria for diagnosis of IBS. Opioid-induced constipation (OIC) is defined as a change from baseline bowel habits and patterns of defecation after initiating opioid therapy that is characterized by reduced bowel movement frequency, development or worsening of straining to pass bowel movements, a sense of incomplete bowel evacuation, or the patient’s perception of stress related to bowel habits.3 OIC is an opioid-induced adverse effect that can overlap with and worsen functional constipation.4 OIC constipation is associated with significant economic burden. In cancer patients taking opioids for pain the incidence of OIC constipation approached 94%.5 Constipation is associated with significant socioeconomic costs and considerable quality-of-life ramifications.5,6 Physiological, environmental, and demographic factors may play ...

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