Constipation is one of the most common outpatient complaints — and one of the most reflexively undertreated and overtreated simultaneously. The clinical skill is identifying the cause, ruling out alarm features and secondary causes, and building a rational regimen rather than adding laxatives without a framework.
CLINICAL PRINTABLE
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A one-page Constipation clinical reference is on the way.
1 · Recognition / Alarm Features
- Rome IV criteria for functional constipation: ≥2 of the following for ≥3 months: straining, lumpy/hard stools, sensation of incomplete evacuation, sensation of anorectal obstruction/blockage, manual maneuvers to facilitate defecation, or <3 spontaneous bowel movements per week.
- Alarm features requiring urgent evaluation: rectal bleeding, unintentional weight loss, iron deficiency anemia, new-onset constipation in patients >50 years, family history of colorectal cancer or IBD, change in stool caliber (pencil-thin stools), or palpable abdominal/rectal mass.
- Secondary causes to exclude: hypothyroidism, hypercalcemia, hypokalemia, diabetes (autonomic neuropathy), Parkinson's disease, multiple sclerosis, spinal cord injury, colorectal cancer, and medications.
- Medication-induced constipation: opioids (most common), anticholinergics, calcium channel blockers (especially verapamil), iron supplements, antacids (calcium/aluminum), antidepressants (TCAs), antipsychotics. Review the medication list at every constipation visit.
- Opioid-induced constipation (OIC): occurs in 40–80% of patients on chronic opioids. Does not improve with time (unlike other opioid side effects). Requires proactive bowel regimen from day 1 of opioid therapy.
2 · Differential / Secondary Causes
Colorectal cancer
New-onset constipation in patients >50 years, change in stool caliber, rectal bleeding, weight loss, or iron deficiency anemia. Colonoscopy is indicated. Do not attribute new constipation to functional causes without ruling out malignancy.
Hypothyroidism
Constipation, fatigue, weight gain, cold intolerance, dry skin, bradycardia. TSH is the screening test. Constipation resolves with thyroid hormone replacement.
Hypercalcemia
Constipation, nausea, polyuria, polydipsia, confusion ('bones, stones, groans, and psychic moans'). Serum calcium and PTH. Treat the underlying cause.
Hirschsprung disease
Congenital absence of ganglion cells in the rectum. Presents in infancy with failure to pass meconium, but can present in adults with lifelong constipation. Rectal biopsy for diagnosis.
3 · Treatment Pathway
Lifestyle and dietary modification
Increase dietary fiber to 25–35 g/day (fruits, vegetables, whole grains, legumes). Adequate fluid intake (1.5–2 L/day). Regular physical activity. Establish a consistent toileting routine (after meals, utilizing the gastrocolic reflex). Elevate feet on a footstool to approximate squatting position.
Osmotic laxatives — first-line
Polyethylene glycol (PEG/MiraLax) 17 g daily: safe, effective, non-habit-forming. Preferred first-line agent. Lactulose 15–30 mL daily: effective but causes more bloating and flatulence. Magnesium hydroxide (milk of magnesia): effective but avoid in renal insufficiency.
Stimulant laxatives
Senna or bisacodyl: stimulate colonic motility. Effective for short-term use and opioid-induced constipation. Historically avoided long-term due to concerns about cathartic colon — current evidence does not support this concern. Appropriate for chronic use when osmotic agents are insufficient.
Opioid-induced constipation (OIC)
Start a stimulant laxative (senna) on day 1 of opioid therapy — do not wait for constipation to develop. Add PEG if senna alone is insufficient. Peripherally acting mu-opioid receptor antagonists (PAMORAs): methylnaltrexone (subcutaneous), naloxegol, or naldemedine for refractory OIC. PAMORAs do not reverse analgesia.
Refractory/chronic constipation
Secretagogues: lubiprostone (activates chloride channels), linaclotide or plecanatide (guanylate cyclase-C agonists) for chronic idiopathic constipation or IBS-C. Prucalopride (5-HT4 agonist) for chronic constipation. Biofeedback therapy for dyssynergic defecation (pelvic floor dysfunction).
Fecal impaction
Manual disimpaction followed by enema (tap water or sodium phosphate). Oral PEG at high dose for proximal impaction. After disimpaction, establish a maintenance bowel regimen to prevent recurrence.
4 · Expected Response
- PEG: onset within 1–3 days. Titrate dose to achieve soft, formed stools — not diarrhea. Patients can use PEG daily long-term safely.
- Stimulant laxatives: onset within 6–12 hours (bisacodyl) or 6–24 hours (senna). Dose at bedtime for morning bowel movement.
- Secretagogues (linaclotide, lubiprostone): onset within 1–2 weeks. Most effective for IBS-C and chronic idiopathic constipation. Diarrhea is the most common side effect — start at low dose.
5 · Escalation
- Alarm features (rectal bleeding, weight loss, iron deficiency anemia, new onset >50 years, change in stool caliber): colonoscopy referral to exclude colorectal cancer.
- Acute colonic pseudo-obstruction (Ogilvie syndrome): massive colonic dilation without mechanical obstruction, typically in hospitalized patients. Neostigmine or colonoscopic decompression. Surgery for perforation or ischemia.
- Refractory constipation not responding to multiple laxative classes: gastroenterology referral for anorectal manometry, defecography, and colonic transit study to identify dyssynergic defecation or slow-transit constipation.
- Fecal impaction with signs of bowel obstruction or perforation: urgent surgical evaluation.
Apply It · Change One Detail
APPLY IT
A 68-year-old man on chronic opioids for back pain reports that he has not had a bowel movement in 5 days. He was started on opioids 3 weeks ago with no bowel regimen. This is opioid-induced constipation — predictable and preventable. Start senna twice daily plus PEG 17 g daily. For future opioid initiations, start the bowel regimen on day 1. OIC does not improve with time, unlike nausea or sedation.
CHANGE ONE DETAIL
Change one detail — a 52-year-old woman with no prior constipation history presents with 6 weeks of constipation, pencil-thin stools, and a 5 kg unintentional weight loss. This is not functional constipation — these are alarm features. Colonoscopy is indicated before any laxative therapy. New-onset constipation with change in stool caliber and weight loss in a patient over 50 is colorectal cancer until proven otherwise.
Bottom Line
Start a bowel regimen on day 1 of opioid therapy — OIC does not improve with time. New-onset constipation with alarm features in patients >50 requires colonoscopy before laxatives.
EVIDENCE & REFERENCES
- Bharucha AE, et al. American Gastroenterological Association technical review on constipation. Gastroenterology. 2013;144(1):218-238. doi:10.1053/j.gastro.2012.10.028
- Camilleri M, et al. Clinical guideline: management of idiopathic chronic constipation. Am J Gastroenterol. 2017;112(1):37-60. doi:10.1038/ajg.2016.507