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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 (IBS) with constipation (IBS-C).

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

  4. Differentiate acute and chronic diarrhea.

  5. Compare diarrhea caused by various infectious agents.

  6. Appraise medication causes of diarrhea.

  7. Construct pharmacotherapeutic strategies for treating diarrhea.

  8. Identify the signs and symptoms of IBS with constipation (IBS-C), diarrhea (IBS-D), or mixed (IBS-M).

  9. Compare and contrast the features of IBS-C, IBS-D, and IBS-M.

  10. Establish treatment goals for IBS.

  11. Evaluate the effectiveness of pharmacotherapy for IBS.


Constipation, diarrhea, and irritable bowel syndrome (IBS) are disorders of the gastrointestinal (GI) tract that have various causes and symptoms. A thorough patient assessment is required to accurately identify the underlying causes 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 Rome IV Foundation provides evidence-based definitions, diagnostic criteria, and classification of FGIDs.1 This chapter is focused on the evaluation and management of constipation, diarrhea, and IBS.


image Constipation, when not associated with symptoms of IBS-C, is characterized by the occurrence of fewer than three spontaneous stools per week. There may also be straining on defecation, lumpy or hard stools, sensation of incomplete evacuation, and the need to use manual maneuvers to facilitate defecation. Occasional constipation usually does not require medical evaluation or treatment. Functional constipation (FC) is defined as infrequent (fewer than three stools per week) or difficult passage of stools or both that lasts for 12 weeks or more and is accompanied by onset of symptoms at least 24 weeks prior to diagnosis. Chronic idiopathic constipation (CIC) is defined as continuing constipation with no known cause or known contributory illness.2


Constipation affects people of all ages and occurs in approximately 16% of all adults and in one-third of adults aged 60 and older. In 2019, US sales of nonprescription laxative products totaled more than $1.4 billion.3 It is estimated that CIC affects 9% to 20% of adults in the United States. A population-based survey determined that 37.6% of respondents had discussed their constipation symptoms with a primary care provider, gastroenterologist, or emergency room physician.4 About 48% of respondents reported that they treated constipation with medication, with 93.5% of those using nonprescription medications alone, 1.3% using prescription medications alone, and 5.2% using both nonprescription and prescription medications.4

Constipation can be due to primary and secondary causes (Table 22–1). Opioid-induced constipation (OIC) is defined as a ...

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