• Clinical science



Constipation is the infrequent, difficult passage of stool with the sensation of incomplete bowel emptying. It is a common condition in all age groups and often occurs without a pathological cause as a result of a low-fiber diet, poor hydration, and/or lack of exercise. However, it may be associated with anatomical or physiological colorectal abnormalities (e.g., colorectal carcinoma, motility disorder in diabetic neuropathy). A thorough patient history and examination are essential in making a diagnosis. The patient may complain of hard, painful stools in the event of changed stool consistency (e.g., caused by poor diet or lack of hydration) or difficult, strained passage of soft stool in the event of altered defecatory behavior (e.g., anatomical obstruction, motility disorder). In the absence of organic disease, constipation may resolve with regular exercise, hydration, and fiber supplementation. Osmotic or secretory laxatives may be considered in patients with unrelenting constipation. Long-term use of laxatives may result in dependency and paradoxical constipation, which can only be relieved with adequate lifestyle changes.


  • Prevalence: ∼ 28% of the general population
  • Sex: > (3:1)
  • Accounts for 3–5% of pediatric outpatient visits
  • 30% more common in non-white populations


Epidemiological data refers to the US, unless otherwise specified.


Constipation may be acute or chronic.

  • Primary (functional): constipation in the absence of an identifiable medical disorder or side effect of medication
    • More commonly due to poor diet and insufficient exercise
    • In children: typically occurs during weaning, the toilet training phase, or once attending school (because of avoidance of school toilets)
  • Secondary: constipation due to a medical disorder or medication

It is important to differentiate between harmless acute constipation and emergency ileus in all age groups!



  • Primary (functional) constipation: further subdivided into slow transit constipation (STC), normal transit constipation (NTC), and outlet constipation
Definition Additional presenting complaints
STC Prolonged colonic transit time, confirmed on a motility study Infrequent "urge" to pass stool, abdominal discomfort, bloating
NTC Normal colonic transit time, despite the perception of constipation by the patient (e.g., psychosocial issues) Abdominal discomfort, bloating
Outlet constipation Lack of coordination (high resistance or low propulsive force) of the pelvic floor muscles during an attempt to pass stool from the rectum Prolonged straining, rectal discomfort, often difficult passage of soft stool, may require manual maneuvering to evacuate stool


Primary or secondary causes may change stool consistency, alter defecation habits, or a combination of both.

Mechanism of altered stool consistency

  • Primary constipation: Changes in stool consistency are often caused by external factors, such as a lack of exercise or inadequate fluid and fiber intake → slow passage of stool → prolonged absorption of water by the bowel → dry, hard stool → painful defecation → sensation of incomplete and irregular bowel emptying → constipation
  • Secondary constipation: very similar to the mechanism to primary constipation; however, slow passage of stool is caused by a structural or biochemical abnormality within the bowels

Mechanism of altered bowel motility

  • Effective peristalsis of the bowel is controlled by intrinsic (e.g., myenteric plexus) and extrinsic (e.g., sympathetic and parasympathetic) innervation.
  • Any alteration in adequate bowel innervation may lead to ineffective peristalsis.
    • Drugs (e.g., calcium channel blockers, opiates, antispasmodics, antidepressants) → altered autonomic outflow and bowel muscle contraction
    • Endocrine pathology (e.g., hypothyroidism) → downregulated bowel motility
    • Neurological pathology (e.g., spinal injury, enteric neuropathy) → disease or trauma of bowel innervation
  • Ineffective peristalsis → difficult passage of stool regardless of stool consistency (e.g., hard or soft) → sensation of incomplete and irregular bowel emptying

Mechanism of constipation due to anatomical changes



Constipation is a clinical diagnosis. It requires a detailed patient history, physical examination, and further testing to identify potential underlying conditions and/or alarming features.

  • Patient history
    • Ask about dietary habits, medication use, mobility, stool character and frequency, problems with defecation, and anorectal pain.
    • Additionally in children: delayed passage of meconium (e.g., Hirschsprung's disease), voluntary withholding of stool (e.g., squatting, crying, crossing ankles, hiding), fecal (overflow) incontinence

Rome III diagnostic criteria for adults

At least two of the following symptoms must have occurred in the past 6 months over at least a 12 week period:

  • Passage of stool frequency < 3 times/week
  • Passage of hard or lumpy stool
  • Sensation of incomplete defecation
  • Manual maneuvering to empty the bowel
  • Straining during attempts to defecate
  • Sensation of anorectal obstruction

Rome III diagnostic criteria for children

At least two of the following symptoms must have occurred over a 1 month period < 4 years OR at least once per week over a 2 month period ≥ 4 years:

  • ≤ 2 defecations per week
  • At least 1 episode of incontinence per week after becoming toilet-trained
  • History of excessive stool retention
  • Painful or hard bowel movements
  • Large fecal mass in the rectum
  • History of a large-diameter stool that may obstruct the toilet

Before diagnosing constipation, irritable bowel syndrome (IBS) must be ruled out!

If enough Rome III diagnostic criteria are fulfilled, constipation is possible even when stool is passed regularly!

  • Physical examination
    • Inspect the anorectal area
    • Digital examination of the rectum
  • Laboratory investigations: exclude hypokalemia, hypothyroidism, diabetes mellitus
  • Imaging: abdominal x-ray
  • Colonoscopy: to exclude mechanical obstruction; (e.g., tumor, stenosis) especially in the presence of alarming features (see table below)
Alarm features in patients with constipation


  • Delayed passage of meconium > 48 hours
  • Constipation when < 1 month old
  • Family history (e.g., Hirschsprung's disease)
  • Bilious vomiting
  • Severe abdominal distention
  • Blood in stool
  • Fever
  • Failure to thrive
  • Possible congenital abnormalities detected on examination (e.g., tuft of hair on spine, sacral dimple, abnormal position of anus)

A reduced stool caliber (i.e. “pencil-shaped stool”) and rectal bleeding in a patient > 40 years of age must be further investigated, as these features may be a sign of colorectal cancer!

Alarm symptoms and signs in patients with constipation suggest a possible underlying condition!


Differential diagnoses

IBS with predominant constipation pattern (IBS-C)


The differential diagnoses listed here are not exhaustive.


  • Treat any underlying conditions.
  • Approach for adults
  • Approach for children
    • 2 weeks–6 months of age, without alarming features
      • May only require reassurance
        • Passage of stool is particularly variable in breastfed infants.
        • Parents who formula feed their children should be properly educated on correct formula preparation.
      • Reassess in 2–4 weeks
      • If constipation persists, consider drug therapy (i.e. polyethylene glycol).
    • Children ≥ 6 months of age without suspected organic disease
      • Prompt laxative therapy (best initial: polyethylene glycol)
      • In combination with age-appropriate fiber, fluid, and physical activity requirements
      • Toilet training education if applicable
    • Maintenance therapy: laxative therapy (polyethylene glycol or lactulose) until constipation is resolved for at least 1 month (treatment should then be tapered gradually)
    • A poor response to the treatments mentioned above or a child < 2 weeks with constipation warrants further investigation to exclude an underlying disorder.
Laxatives (purgatives)
Mechanism of action Agent Characteristics
Emollient stool softeners
  • Stool softener: emulsifies and softens the stool for easier passage through the intestinal tract
  • Dioctyl sodium sulfosuccinate is administered rectally
  • Liquid paraffin should not be used in the presence of foreign body granulomas
Bulk-forming agents
  • Indigestible, not systemically absorbed
  • Bulks up due to water absorption in the intestinal lumen → Stretching of the bowel wall stimulates peristalsis.
Osmotic laxatives
  • Work by pulling water into the intestinal lumen, thereby stimulating intestinal motility
  • PEG is effective and well tolerated.
  • Salts are partially reabsorbed and may cause a shift in electrolytes (hypernatremia, hypermagnesemia).
  • Glauber's salt is no longer used as treatment for constipation.
  • Carbohydrates can cause severe flatulence due to bacterial degradation.
  • Lactulose is also used to treat hepatic encephalopathy.
  • Sorbitol and mannitol are used as enemas.
Stimulative (also secretory) laxatives
  • Increased water secretion into the lumen due to Cl-secretion
  • For short-term use only, as they may result in severe water and potassium loss
  • Bisacodyl and sodium picosulfate are anthraquinolones and may result in melanosis coli.
  • Patients may become dependent on laxatives with prolonged use.
    • Long-term use of OTC laxatives may cause water and electrolyte imbalances in the bowel, paradoxically resulting in further constipation.
    • Adequate lifestyle changes are the only way to break this cycle of constipation.
  • Opiate-induced constipation: Methylnaltrexone bromide, a peripheral acting opioid receptor antagonist, may be considered when treatment with the laxatives mentioned above does not produce adequate results.

Patients who suffer from severe potassium loss due to laxative therapy may develop hypokalemia, which also reduces bowel motility!

Chronic use of laxatives may lead to drug dependency!




We list the most important complications. The selection is not exhaustive.