Constipation — Causes, Treatment & When to See a Doctor — Causes, Diagnosis & When to See a Doctor | MyMedicPlus

Constipation is one of the most common gastrointestinal complaints worldwide, affecting up to 20% of the adult population at any given time. It is clinically defined as having fewer than 3 bowel movements per week, combined with one or more of the following: hard or lumpy stools (Bristol Stool Chart type 1 or 2), significant straining, a sensation of incomplete rectal emptying, a sensation of anorectal obstruction or blockage, or the need for manual manoeuvres to assist defecation in more than 25% of bowel movements. These criteria, established by the Rome IV diagnostic consensus, help distinguish constipation from normal variation in bowel frequency, which ranges widely between individuals — from 3 movements per day to 3 per week. Constipation is significantly more common in women than men, in older adults (affecting up to 40% of those over 65), in people with low physical activity, and in pregnant women due to hormonal effects on bowel motility. While most constipation is functional (primary constipation) with no serious underlying cause, it can also be secondary to systemic medical conditions, medications, or — in a minority of cases — serious structural pathology including colorectal cancer. The overall impact on quality of life, including bloating, discomfort, pain, and lost productivity, is substantial.

Inadequate dietary fibre is the most common primary cause — most adults consume only 15–17g of fibre daily, well below the recommended 25–38g. Insufficient fluid intake causes the colon to reabsorb more water from stool, making it hard and difficult to pass. Physical inactivity reduces colonic peristalsis, slowing transit time. Opioid analgesics (morphine, codeine, tramadol, fentanyl) cause opioid-induced constipation through mu-receptor activation in the gut wall, reducing propulsive contractions — this affects up to 81% of opioid users. Tricyclic antidepressants, anticholinergic drugs, calcium channel blockers, iron supplements, and aluminium-containing antacids all commonly cause constipation. Hypothyroidism reduces intestinal motility and is a frequently overlooked reversible cause — along with hypercalcaemia and hypokalaemia (electrolyte abnormalities). Irritable bowel syndrome (IBS) constipation-predominant type (IBS-C) is characterised by chronic constipation with abdominal pain relieved by defecation and is one of the most common functional causes. Parkinson's disease, multiple sclerosis, and spinal cord lesions cause constipation through neurological disruption of bowel motility. Depression is independently associated with constipation through the gut-brain axis. Pelvic floor dysfunction — dyssynergic defecation, where the pelvic floor muscles paradoxically contract rather than relax during straining — prevents normal evacuation. Rarely, colorectal cancer causes new-onset constipation or change in bowel habit, especially in older adults.

Most constipation is benign, but certain accompanying features constitute red flags demanding urgent medical evaluation to exclude serious underlying pathology. Seek medical attention promptly — ideally within a few days — for any of the following: blood in or on the stool, which may appear bright red (rectal bleeding) or mixed through dark stool; unexplained weight loss of more than 5% of body weight over 3–6 months alongside constipation; new onset of constipation or a definite unexplained change in usual bowel habit in an adult over 50, particularly without a dietary or medication explanation; pencil-thin or ribbon-like stools that persist over multiple bowel movements, suggesting a possible stricture or mass causing luminal narrowing; severe or worsening abdominal pain or cramping, particularly if associated with distension and vomiting, raising concern for bowel obstruction; iron-deficiency anaemia unexplained by diet or menstrual loss combined with altered bowel habit. Constipation alternating regularly with episodes of diarrhoea warrants investigation for IBS, coeliac disease, or inflammatory bowel disease. Absolute constipation — inability to pass gas or stool — with abdominal distension constitutes a potential bowel obstruction requiring emergency evaluation.

Clinical history and physical examination form the foundation of constipation diagnosis. The physician establishes the duration, frequency, stool consistency (Bristol Stool Chart), straining, sense of incomplete evacuation, use of manual manoeuvres, and prior bowel habit. A thorough medication review is essential, as drug-induced constipation is frequently missed. Dietary history, fluid intake, and activity level are assessed. Physical examination includes abdominal palpation for faecal loading and distension, and a digital rectal examination to assess stool consistency, rectal tone, perineal descent, and pelvic floor function — this often provides critical information. Blood tests check thyroid function (TSH), serum calcium, blood glucose, and full blood count (to detect anaemia suggesting blood loss). A colonoscopy or flexible sigmoidoscopy is recommended when red flag features are present, when the patient is over 50 with a change in bowel habit, or when initial measures have failed and secondary causes need exclusion. In refractory cases, colonic transit studies (radio-opaque marker studies or scintigraphy) quantify transit time and identify slow-transit constipation. Anorectal manometry and defecography assess pelvic floor function in suspected dyssynergic defecation.

First-line management is dietary and lifestyle modification, which resolves constipation in the majority of patients. Increase dietary fibre intake gradually over 2–4 weeks to 25–38g per day through fruits, vegetables, legumes, whole grains, and nuts — abrupt increase causes bloating, so gradual introduction is important. Increase fluid intake to at least 1.5–2 litres of water daily, as fibre requires water to form soft bulky stools. Increase daily physical activity — even brisk walking significantly improves colonic motility. Respond promptly to the urge to defecate rather than suppressing it. Adopting a squatting position (using a footstool to raise the feet while seated on the toilet) straightens the anorectal angle and facilitates easier evacuation. If dietary measures are insufficient, add bulk-forming laxatives (psyllium husk, methylcellulose, ispaghula) — these require adequate fluid intake to be effective and should be taken with at least 200–300 mL of water. Osmotic laxatives (polyethylene glycol 3350 — Macrogol or Movicol — and lactulose) are safe for regular use and are first-line pharmacological options. Stimulant laxatives (senna, bisacodyl) are effective for short-term use and are appropriate for opioid-induced constipation. For opioid-induced constipation, peripherally acting mu-opioid receptor antagonists (PAMORAs) such as naloxegol or methylnaltrexone are specifically indicated. Linaclotide and prucalopride are licensed for chronic idiopathic constipation unresponsive to standard laxatives. Biofeedback therapy is effective for pelvic floor dyssynergia.

A high-fibre diet is the cornerstone of constipation prevention — aim for at least 25–38g of dietary fibre per day from a variety of sources including whole grain bread and cereals (particularly oat bran and wheat bran), fruits (especially prunes, pears, and apples with skin), vegetables (particularly broccoli, leafy greens, and carrots), and legumes (beans, lentils, chickpeas) which are among the richest fibre sources. Drink adequate fluids throughout the day — at least 1.5–2 litres of water or other non-caffeinated beverages — as dehydration is a major contributor to hard stools. Exercise daily: even 20–30 minutes of brisk walking activates the gastrocolic reflex and promotes colonic transit. Develop a regular bowel routine — attempt defecation at the same time each day, preferably 20–30 minutes after breakfast when the gastrocolic reflex is most active. Respond immediately to the urge to defecate rather than delaying; repeatedly suppressing the urge weakens the defecatory reflex over time. Review current medications with your doctor if constipation developed after starting a new drug — alternatives may be available. Manage stress, as psychological stress is a well-recognised trigger for IBS-related constipation through the gut-brain axis.

Seek emergency care or call 999/112 for constipation with complete absence of bowel movements and inability to pass gas for more than 24–48 hours combined with significant abdominal distension, pain, and vomiting — this may represent bowel obstruction. Attend the emergency department for severe abdominal pain with constipation following an abdominal operation (anastomotic or mechanical obstruction risk). Seek urgent same-week GP assessment for new-onset constipation in an adult over 50 without an obvious explanation, blood in or on the stool, unexplained weight loss, or iron-deficiency anaemia alongside constipation. Schedule a routine GP appointment for constipation that has persisted despite 3 weeks of first-line dietary and lifestyle modification, for constipation alternating with diarrhoea, for pencil-thin stools, or for constipation significantly affecting quality of life. Constipation in children, particularly with pain, soiling (overflow incontinence around impacted stool), or withholding behaviour, always warrants paediatric review. Constipation in pregnancy is common but rectal bleeding, severe pain, or failure of conservative measures requires obstetric or gastroenterological review.