PassFinals
Gastroenterology & Nutrition

Constipation

Constipation is unsatisfactory defaecation because stools are infrequent, hard, difficult or incomplete; most is functional or medication-related and responds to a stepwise laxative plan, but obstruction, impaction and colorectal-cancer symptoms must be recognised before routine treatment.

In a nutshell

Constipation is unsatisfactory defaecation from hard, infrequent or difficult/incomplete stools. Start with history, examination and reversible causes. Use lifestyle measures and the NICE laxative ladder, but first exclude obstruction and faecal impaction. Opioid-induced constipation needs regular laxatives from the outset and usually osmotic/stimulant treatment. Unexplained bowel-habit change, bleeding, anaemia, weight loss or a mass needs the current FIT/colorectal pathway.

Classic presentation

An older person on morphine develops hard stools, straining and overflow soiling; examination finds faecal loading and the opioid regimen has no regular laxative.

Key points

  • Constipation is a symptom pattern, not a universal stool-frequency threshold.
  • First exclude obstruction, impaction and colorectal-cancer red flags before escalating laxatives.
  • Use lifestyle measures and a stepwise bulk-forming -> osmotic -> stimulant plan when appropriate.
  • Macrogol is an osmotic laxative used for constipation and faecal impaction; follow the product/BNF regimen.
  • Strong opioids should be prescribed with regular laxative treatment; refractory opioid constipation may need a PAMORA.
  • Overflow diarrhoea may be impaction, not infection; clear the stool burden after obstruction is excluded.
  • Unexplained change in bowel habit, bleeding, anaemia, weight loss or mass needs current NICE colorectal assessment/FIT.

First-line investigation

Clinical history and abdominal examination, with rectal examination, blood tests, FIT or imaging only when impaction, systemic disease, obstruction or cancer is suspected.

Management

Exclude obstruction and impaction

  • Assess vomiting, distension, severe pain, absolute constipation, peritonism, mass, neurological symptoms and overflow soiling before giving escalating oral laxatives.1,2

Correct causes and use lifestyle measures

  • Review medicines, fibre, fluids, mobility and toilet access; treat reversible contributors while respecting fluid restrictions and obstruction risk.1,3

Use the laxative ladder

  • Use a bulk-forming agent when appropriate, then macrogol/another osmotic if stools remain hard, and add a stimulant when stools are soft but difficult to pass; follow BNF/product-specific regimens.1,3,8

Treat opioid constipation and refractory disease

  • Prescribe regular laxatives with strong opioids; optimise osmotic/stimulant treatment and consider a NICE-approved PAMORA after inadequate response. Refer refractory chronic constipation for specialist assessment.4,6,5,9

Safety-net cancer and impaction features

  • Review response, hydration, adverse effects and recurrence; arrange FIT/colorectal assessment for unexplained bowel-habit change or other red flags and reassess recurrent impaction or overflow.2,7,1

Exam traps

  • Do not give bulk-forming or high-volume laxatives when bowel obstruction is possible.
  • Overflow soiling in an impacted patient is not automatically infective diarrhoea.
  • Do not use routine abdominal X-ray to diagnose uncomplicated constipation.
  • Strong opioids need prophylactic regular laxatives; bulk-forming treatment alone is not the usual opioid strategy.
  • A negative FIT does not overrule a mass or persistent high clinical suspicion.
  • Prucalopride is a specialist option after adequate trials of laxatives, not an early substitute for macrogol.

Illustrations

Bristol Stool ChartThe Bristol Stool Chart showing types 1 to 7, with types 1 and 2 illustrating hard/lumpy stool. Include a note that stool form is only one part of the constipation history.Cabot Health, Bristol Stool Chart, Wikimedia Commons · CC-BY-SA-3.0
Faecal loading on an abdominal radiographA radiograph illustrating faecal loading, labelled as a selected specialist investigation rather than a routine diagnostic test for uncomplicated constipation.James Heilman, MD, Wikimedia Commons · CC-BY-3.0

Key sources

  1. NICE CKS, Constipation (Clinical Knowledge Summary, adult constipation)
  2. NICE NG12, Suspected cancer: recognition and referral (Last updated 15 April 2026; colorectal cancer recommendations)Updated 15 Apr 2026
  3. NHS, Macrogol (NHS medicines information, current page)
  4. NICE CG140, Palliative care for adults: strong opioids for pain relief (Recommendations on prescribing regular laxatives with strong opioids)
  5. NICE TA651, Naldemedine for opioid-induced constipation (Technology appraisal, published 30 September 2020)Updated 30 Sept 2020
  6. NICE TA345, Naloxegol for opioid-induced constipation (Technology appraisal, published 22 July 2015; reviewed 9 July 2018)Updated 9 Jul 2018
  7. NICE HTG690, Quantitative faecal immunochemical testing (Recommendations for suspected colorectal cancer referral, published 24 August 2023)Updated 24 Aug 2023
  8. BNF, Laxatives (BNF prescribing and bowel-cleansing monographs)
  9. NICE TA211, Prucalopride for chronic constipation in women (Technology appraisal recommendations, published 15 December 2010)Updated 15 Dec 2010

This page is exam revision material, not medical advice, and must not be used for patient care. Always check drug doses against the BNF and current guidance. Full disclaimer.