Constipation — Causes, Bristol Stool Scale, Laxatives & Treatment Guide — Symptoms, Causes & Treatment | MyMedicPlus

Constipation is defined by the Rome IV criteria as two or more of the following symptoms occurring for at least 25% of defecations over 3 months: fewer than 3 spontaneous bowel movements per week, hard or lumpy stools (Bristol Stool Scale types 1-2 — hard pellets or sausage-shaped with lumps), excessive straining during defecation, sensation of incomplete evacuation, sensation of anorectal blockage, or manual manoeuvres required to facilitate defecation. It is one of the most common gastrointestinal complaints worldwide, affecting approximately 14% of adults globally, with significantly higher prevalence in women, the elderly, and those with low dietary fibre intake, physical inactivity, or medication side effects. Constipation is classified as primary (functional — without identifiable organic cause, subdivided into normal-transit, slow-transit, and defaecatory dysfunction) or secondary (caused by an underlying condition or medication). Chronic functional constipation significantly impairs quality of life and is frequently undertreated, despite effective therapies being available.

Primary (functional) constipation: inadequate dietary fibre (under 25g/day), insufficient fluid intake, physical inactivity, ignoring the urge to defecate, psychological stress, and poor toilet habits (rushed defecation posture, avoiding public toilets). Slow-transit constipation: impaired colonic motility. Pelvic floor/outlet dysfunction (dyssynergic defecation): failure of puborectalis and external anal sphincter to relax during straining. Secondary causes requiring investigation: medications (opioids — most common drug cause, anticholinergics, calcium channel blockers, iron supplements, antidepressants, antacids, NSAIDs); hypothyroidism; hypercalcaemia; diabetes (autonomic neuropathy reducing colonic peristalsis); Parkinson's disease; colorectal cancer (any new change in bowel habit in adults over 50); pregnancy; IBS with constipation (IBS-C); and spinal cord injury or multiple sclerosis affecting enteric innervation.

Infrequent stools (fewer than 3 per week); hard, dry, lumpy stools requiring straining (Bristol Stool Scale types 1-2); sensation of incomplete evacuation; bloating and abdominal discomfort; and need for digital rectal manoeuvres in severe cases. Anal complications from chronic straining: haemorrhoids (piles), anal fissure (painful tear causing bright red bleeding with defecation), and rectal prolapse. Red flag symptoms requiring urgent investigation: blood mixed in stools (not just on toilet paper), unintentional weight loss, new change in bowel habit in adults over 40 years of age, iron deficiency anaemia, and a palpable abdominal or rectal mass — these symptoms may indicate colorectal cancer and should always prompt urgent colonoscopy referral.

Constipation is diagnosed clinically. History: frequency, stool consistency (Bristol Stool Scale), duration, medication review, dietary habits, and red flag symptoms. Physical examination: abdominal palpation (faecal loading, mass); rectal examination (faecal impaction, anal tone, puborectalis function, rectal prolapse). Investigations for red flags or secondary causes: FBC (anaemia), thyroid function (hypothyroidism), serum calcium, glucose (diabetes), colonoscopy (if red flag symptoms or age over 50 with new-onset constipation). Specialist investigations for refractory constipation: colonic transit study (radio-opaque markers to assess transit time — normal under 72 hours); anorectal manometry and balloon expulsion test (assess pelvic floor function and diagnose dyssynergic defecation); defaecating proctogram (MRI/fluoroscopy during straining).

First-line: dietary modification — increase fibre to 25-30g/day gradually (wholemeal bread, bran cereals, oats, fruits with skin, vegetables, legumes); increase fluid intake to 1.5-2 litres/day; regular exercise (30 minutes daily — promotes colonic motility). Establish a regular toilet routine: use the toilet 20-30 minutes after breakfast (gastrocolic reflex); use a footstool to elevate feet, creating a squatting posture. Laxatives: osmotic laxatives — first-line drug treatment; polyethylene glycol (Macrogol/Movicol/Laxido) draws water into the colon; lactulose (slower, more gas); magnesium salts (magnesium hydroxide, magnesium citrate). Stimulant laxatives — senna, bisacodyl, sodium picosulfate — stimulate colonic peristalsis; effective for acute constipation but avoid prolonged use without specialist guidance. Stool softeners — docusate sodium — for hard stools. Rectal preparations — glycerin suppositories, phosphate enemas — for faecal impaction. Newer agents for chronic/IBS-C: prucalopride (5-HT4 receptor agonist — stimulates colonic motility), linaclotide/plecanatide (guanylate cyclase agonists — for IBS-C and chronic idiopathic constipation). Biofeedback therapy for dyssynergic defecation.

Chronic constipation causes local anorectal complications and broader health consequences. Haemorrhoids (piles): straining at stool increases venous pressure in the haemorrhoidal plexus — internal haemorrhoids cause painless bright red rectal bleeding; external haemorrhoids cause perianal pain, swelling, and thrombosis. Anal fissure: hard stool tears the anoderm, causing severe pain on defaecation, fresh bleeding, and sphincter spasm — acute fissures are treated with topical glyceryl trinitrate (GTN 0.4%) or diltiazem cream; chronic fissures may require botulinum toxin injection or lateral internal sphincterotomy. Rectal prolapse: excessive straining causes the rectal wall to prolapse through the anus — more common in elderly women. Faecal impaction: hard stool becomes lodged in the rectum, causing paradoxical overflow diarrhoea in elderly patients — frequently misdiagnosed as infective diarrhoea and incorrectly treated with antidiarrhoeals, worsening the impaction; treatment requires manual disimpaction and enemas. Acute colonic pseudo-obstruction (Ogilvie's syndrome): massive colonic dilatation without mechanical obstruction — risk of caecal perforation at diameters above 12 cm. In children, chronic constipation impairs bladder function — causing urinary frequency, urgency, and recurrent urinary tract infections from bladder compression.

Increase dietary fibre gradually (to avoid excessive wind/bloating) — aim for 25-30g/day. Include fibre from varied sources: soluble fibre (oats, psyllium, fruits, vegetables — softens stools); insoluble fibre (wholemeal bread, bran, lentils — bulks stools). Drink 1.5-2 litres of fluid daily — fibre requires water to work. Exercise regularly — even a 20-minute daily walk promotes bowel motility. Never ignore the urge to defecate — delaying increases colonic water reabsorption and stool hardness. Use a correct toilet posture — feet elevated on a footstool to simulate the natural squatting angle (30-degree forward lean). Review medications with your GP if constipation is a side effect. Avoid regular stimulant laxative use without medical supervision. Pre-emptively prescribe osmotic laxatives for all patients starting opioid therapy.

See a GP for: constipation lasting more than 3 weeks that does not respond to dietary changes and laxatives, constipation associated with blood in the stool or rectal bleeding (which must always be investigated to exclude colorectal cancer), significant unexplained weight loss, a palpable abdominal or rectal mass, iron-deficiency anaemia without an obvious cause, or a change in bowel habit in a person over 40 after a period of normal habit. Seek urgent (same-day) or emergency assessment for: complete inability to pass stool or flatus with severe abdominal distension (possible complete bowel obstruction — requires emergency imaging and surgical assessment); severe colicky abdominal pain; or signs of large bowel volvulus. Any new constipation in a person over 50 without a clear cause warrants flexible sigmoidoscopy or colonoscopy to exclude colorectal cancer — this is particularly important if there is a family history of bowel cancer, rectal bleeding, or a positive faecal immunochemical test (FIT).