Table 1.

Pharmacological mechanisms and clinical symptoms of opioid-induced bowel dysfunction

Pharmacological mechanisms	Clinical symptoms
Decreased saliva production	Xerostomia
Dysmotility of the lower esophageal sphincter	Gastro-esophageal reflux (or, rarely, dysphagia)
Decreased gastric secretion, emptying and motility	Delayed absorption of medication, upper abdominal discomfort
Disturbed fluid secretion and absorption	Constipation
Abnormal bowel motility, increased resting contractile tone in the	Straining, incomplete bowel evacuation, bloating, abdominal
small and large intestinal circular muscles, and sphincter dysfunction	distension, constipation
Increased amplitudes of non-propulsive segmental bowel contractions	Spasm, abdominal cramps and pain, stasis of luminal contents, and hard dry stool
Constriction of sphincter of Oddi	Biliary colic, epigastric discomfort, and pain
Increased anal sphincter tone and impaired reflex relaxation during rectal distension	Evacuation disorders
Diminished intestinal, pancreatic, and biliary secretion	Hard, dry stools
Abnormal bowel motility, increased fermentation and meteorism, opioid-induced hyperalgesia	Chronic visceral pain
Central effects of opioids	Nausea and vomiting, anorexia

Notes: Adapted from: Springer International Publishing AG; Drugs; Opioid-induced bowel dysfunction: pathophysiology and management; 72(14); 2012; 1847–1865; Brock C, Olesen SS, Olesen AE, Frøkjaer JB, Andresen T, Drewes AM; Copyright © Springer International Publishing AG 2012; with kind permission of Springer Science+Business Media.12