What is constipation?
Constipation is not simply about going less often. Clinically, it is defined as a pattern of difficult, infrequent, or incomplete bowel movements — and it is more nuanced than most people realise. The widely used Rome IV criteria (the international diagnostic framework for functional gut disorders) describe constipation as having two or more of the following in at least a quarter of bowel movements: straining, passage of lumpy or hard stools, a sensation of incomplete emptying, a sensation of blockage, needing to use manual manoeuvres to help pass stool, or fewer than three spontaneous complete bowel movements per week.1
It is worth knowing what the normal range actually is. Normal bowel frequency in adults spans from three times a day to three times a week — a wide range. Constipation is not simply having fewer stools than average; it is when the difficulty, discomfort, or infrequency begins to cause problems for that person.
Constipation is divided into primary and secondary types. Primary (also called functional or idiopathic) constipation has no identifiable underlying cause — it includes slow-transit constipation (where the bowel moves contents more slowly than usual), pelvic floor dysfunction (also called outlet obstruction or dyssynergia, where the muscles involved in defecation do not coordinate properly), and IBS-C (irritable bowel syndrome with constipation predominance, where pain and bloating accompany constipation). Secondary constipation has an identifiable cause — most commonly medication, but also conditions such as hypothyroidism (an underactive thyroid gland), diabetes, and neurological conditions such as Parkinson's disease.
Common contributing factors include low dietary fibre intake, insufficient fluid intake, a sedentary lifestyle, and medications. Drug-induced constipation is particularly common and often overlooked. Opioids (strong painkillers such as morphine or codeine) are the most potent cause. Other significant culprits include iron supplements, tricyclic antidepressants, calcium channel blockers (a class of blood pressure medication), some antacids (those containing calcium or aluminium), and certain antihistamines.
Why does it matter?
Constipation is genuinely common. Around 1 in 7 adults in the UK has constipation at any given time, and it affects women twice as often as men.1 It is more prevalent in older adults, during pregnancy, and in people taking multiple medications. For many, it is an intermittent nuisance; for others, it becomes a chronic condition that significantly affects daily life and wellbeing.
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NHS burden is substantial. In England, constipation generates around 18.6 million laxative prescriptions per year and accounts for approximately 83,000 hospital admissions annually — a significant and often preventable drain on NHS resources.2
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Impact on quality of life is frequently underestimated. Persistent constipation causes discomfort, bloating, and pain. It can affect mood, sleep, productivity, and social confidence. Studies consistently show it reduces quality of life to a degree that surprises those who have not experienced it chronically.
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Complications can develop. Prolonged straining contributes to haemorrhoids (swollen blood vessels in and around the rectum and anus) and anal fissures (small tears in the anal lining). In severe cases, faecal impaction — where a mass of hard stool becomes lodged — can cause overflow diarrhoea, urinary problems, and occasionally bowel obstruction.
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Medication is a frequently missed cause. Drug-induced constipation is common in people taking opioid painkillers, iron supplements, or certain blood pressure and antidepressant medications — and is often correctable once identified.
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In some cases it is the presenting symptom of something else. A new change in bowel habit — particularly in older adults — warrants attention, because constipation can occasionally be the first sign of a bowel condition that requires investigation.
What your doctor might discuss
When constipation prompts a GP visit, the assessment usually starts with a detailed history. A doctor will typically want to understand the duration of the problem, stool frequency and consistency (the Bristol Stool Chart — a visual scale from type 1, very hard lumpy stools, to type 7, entirely liquid — is often used), any recent change in bowel habit, associated symptoms such as bloating, pain, or rectal bleeding, and a full review of current medications.
- Rectal bleeding, particularly in adults over 50 or with no obvious cause
- Unexplained weight loss alongside a change in bowel habit
- A new change in bowel habit lasting more than six weeks in adults over 50
- Iron deficiency anaemia (low blood iron without an obvious explanation)
- A palpable abdominal or rectal mass
- A family history of bowel cancer or inflammatory bowel disease
- Nocturnal symptoms — symptoms that consistently wake someone from sleep
Physical examination includes abdominal palpation (feeling the abdomen for bloating, tenderness, or a palpable mass of stool). A digital rectal examination — where the doctor gently examines the rectum internally — may be performed to assess for faecal loading, anal tone, and pelvic floor function. This is a normal and important part of the assessment, not something to be concerned about.
In uncomplicated cases without red flags, investigation is not usually required. Blood tests may be arranged to rule out secondary causes — thyroid function, calcium levels, and blood glucose are common checks. Referral to gastroenterology or colorectal surgery is considered if the presentation is atypical, if red flags are present, or if constipation has not responded to standard treatment after several months.
First-line advice is always dietary and lifestyle: increasing dietary fibre (aiming for 30g per day from fruits, vegetables, legumes, and wholegrains), adequate fluid intake (approximately 1.5–2 litres per day), regular physical activity, and good toileting habits — responding promptly to the urge to defecate, not suppressing it, and where practical using a small footstool to raise the feet slightly while on the toilet (which straightens the anorectal angle and can make defecation easier).
When lifestyle measures are insufficient, NICE guidance recommends a stepwise approach to laxatives:1
What the research shows
Two questions drive most of the research in constipation management: which laxatives work best, and how effective are dietary and lifestyle interventions? The evidence on both is reasonably solid — with one clear message on laxatives, and a more nuanced picture on fibre.
superior
This Cochrane review pooled all available randomised controlled trials (RCTs — where participants are randomly assigned to treatment or control, the gold standard of trial design) comparing macrogol (polyethylene glycol / PEG) with lactulose for chronic constipation. Ten RCTs with a combined 868 participants were included.
The finding was clear: macrogol was superior to lactulose on every outcome measured — stool frequency per week, stool consistency (as assessed by the Bristol Stool Chart), relief of abdominal pain, and the need for additional laxative products. Macrogol also produced less gas and bloating, because — unlike lactulose — it is not fermented by gut bacteria.
The authors' conclusion: polyethylene glycol should be used in preference to lactulose in the treatment of chronic constipation. This recommendation is now reflected in NICE guidance for adults.
This systematic review and meta-analysis examined the effect of fibre supplementation (including psyllium / ispaghula husk and other prebiotic fibres) on chronic constipation in adults. The finding showed a clear benefit: 77% of people on fibre supplementation responded to treatment, compared with 44% on placebo — a relative risk (RR — how much more likely an outcome is in one group vs another) of 1.71 (95% CI 1.20–2.42, P=0.003).3
Fibre also significantly increased stool frequency (standardised mean difference 0.39, P=0.03) and softened stool consistency. Psyllium (the fibre in ispaghula husk / Fybogel) showed the most consistent benefits across outcomes.
Importantly, the evidence is for fibre supplements (such as ispaghula husk) rather than simply increasing whole foods in the diet — though dietary fibre is still strongly recommended by NICE as part of first-line management. The trial data for dietary change alone is less robust, largely because it is harder to study rigorously.
Putting it all together
Constipation is one of the most common conditions managed in primary care — and one of the most commonly dismissed. It affects around 1 in 7 UK adults at any given time, causes real distress and discomfort, and generates enormous NHS expenditure that is, in many cases, preventable.
The evidence base for treatment is actually quite reassuring. Dietary and lifestyle changes — particularly adequate fibre, fluid, and activity — are effective first-line interventions with solid supporting data. Where these are insufficient, the research is clear that macrogol (Movicol, Laxido) is the preferred osmotic laxative, outperforming lactulose across every measured outcome. Stimulant laxatives such as senna and bisacodyl provide an effective next step, and more targeted treatments exist for specific subtypes.
One practical point that is often overlooked: toileting habits and position matter. Responding promptly to the urge to defecate, not delaying or suppressing it, and using a small footstool to raise the feet while sitting can make a genuine difference to how easy it is to go. The body's defecation reflex is a physiological process — working with it rather than against it is a simple and cost-free first step.
Constipation can be treated effectively in most cases. If it is persistent, significantly affecting daily life, accompanied by any of the red flag symptoms listed above, or if over-the-counter measures are not helping — anything personally relevant is a conversation for you to have with your GP or healthcare professional.