- 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 a lack of exercise. However, it may be also associated with anatomical or physiological colorectal abnormalities (e.g., colorectal carcinoma, motility disorder in diabetic neuropathy). In the context of constipation, hard, painful stools typically indicate a nutritional cause (e.g., poor diet or lack of hydration), while the difficult, strained passage of soft stool may indicate an organic cause (e.g., anatomical obstruction, motility disorder). Any identifiable underlying cause should be managed accordingly. 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 persisting constipation. Long-term use of laxatives may result in dependency and paradoxical constipation, which can only be relieved with adequate lifestyle changes.
- Prevalence: ∼ 14% of the general population experiences chronic constipation 
- 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.
- By course: acute or chronic
- Primary (functional): constipation in the absence of an identifiable medical disorder
- Secondary: constipation due to a medical disorder or medication 
Acute-onset constipation should raise suspicion of bowel obstruction!
- Most 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) 
- Mechanical: obstruction caused by , diverticulosis, thrombosed hemorrhoids, colonic strictures, volvulus
- Drugs: ; , iron supplements; , antacids, anticholinergics, antidepressants, calcium channel blockers, bile acid resins
- Endocrine/metabolic: ; , ; , electrolyte imbalance (especially ; ), hyperparathyroidism
- Neurological: , diabetic neuropathy; , stroke; , ; , Parkinson disease; , Chagas disease (megacolon), botulism
- Connective tissue disorders: scleroderma, amyloidosis
- Irritable bowel syndrome
Both primary and secondary constipation may cause changes in stool consistency and defecation habits.
Mechanism of altered stool consistency
- External factors such as lack of exercise or inadequate fluid and fiber intake (primary constipation)/internal factors such as changes within the colon or rectum (secondary constipation) → slow passage of stool → prolonged absorption of water by the bowel → dry, hard stool → painful defecation → sensation of incomplete and irregular bowel emptying → constipation.
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 bowel innervation may lead to ineffective peristalsis.
- Drugs (e.g., calcium channel blockers, , antispasmodics, antidepressants)  → altered autonomic outflow and bowel muscle contraction 
- Endocrine pathology (e.g., 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 → sensation of incomplete and irregular bowel emptying
Constipation is a clinical diagnosis. Identifying potential underlying conditions and/or alarming features requires a detailed patient history, physical examination, and further testing.
- 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 disease), voluntary withholding of stool (e.g., squatting, crying, crossing ankles, hiding), fecal (overflow) incontinence
At least two of the following must have occurred in ≥ 1/4 of defecations during the past 12 weeks with onset of symptoms ≥ 6 months ago:
- 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) 
Alarming features in patients with constipation
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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 !
- Diagnose and treat any underlying conditions.
Approach in adults
- Begin with lifestyle changes: high-fiber diet; (psyllium seed husk, wheat bran), increased fluid intake; , and exercise
- If constipation continues: administer osmotic laxatives
- Replace with stimulant laxatives if osmotic laxatives are unsuccessful
- Biofeedback training may be helpful in treating disturbances in defecation.
Approach in children 
Infants 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 (best initial: polyethylene glycol).
- May only require reassurance
- Children ≥ 6 months of age without suspected organic disease
- 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.
- Infants 2 weeks–6 months of age, without alarming features
|Agents||Mechanism of action||Adverse effects|
|Emollient stool softener|| |
|Bulk-forming laxatives|| || |
|Osmotic laxatives|| |
|Stimulant laxatives/secretory laxatives|| |
- 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.
Patients with severe potassium loss due to laxative therapy may develop hypokalemia, which further reduces bowel motility!
Chronic use of laxatives may lead to dependency!