Table 1.

Underlying mechanisms, symptoms, and the potential effects of PAMORAs and laxatives, respectively

Underlying mechanisms	Symptoms	Potential effects of PAMORAs	Potential effects of laxatives
Decreased saliva production	Xerostomia	No, centrally mediated	No
Dysmotility of the lower esophageal sphincter	Gastro-esophageal reflux (or rarely dysphagia)	Yes	No
Decreased gastric secretion, emptying, and motility	Delayed absorption of medication, upper abdominal discomfort	Yes	No
Disturbed fluid secretion and absorption	Constipation	Yes	Depending on type, can increase secretion/osmosis, primarily in colon
Abnormal bowel motility, increased resting contractile tone in the small and large intestinal circular muscles and sphincter dysfunction	Straining, incomplete bowel evacuation, bloating, abdominal distension, constipation	Yes	Stimulant laxatives can stimulate bowel motility under certain circumstances
Increased amplitudes of non-propulsive segmental bowel contractions	Spasm, abdominal cramps and pain, stasis of luminal contents, and hard dry stool	Yes	No
Constriction of sphincter of Oddi	Biliary colic, epigastric discomfort and pain	Yes	No
Increased anal sphincter tone and impaired reflex relaxation during rectal distension	Evacuation disorders	Yes	No
Diminished intestinal, pancreatic, and biliary secretion	Hard dry stools	Yes	Depending on type, can increase secretion/osmosis, primarily in colon
Abnormal bowel motility, increased fermentation and meteorism, opioid-induced hyperalgesia	Chronic visceral pain	Yes	No
Central effects of opioids	Nausea and vomiting, anorexia	No	No

Notes: Most of the potential effects of PAMORAs have not been, or only partly, substantiated in clinical trials, but as they target the underlying mechanism they could in theory have an effect on many of the symptoms.

Abbreviation: PAMORAs, peripherally acting, μ-opioid receptor antagonists.