What is the NHS definition of constipation?

The NHS lists these signs of constipation: not having pooed at least three times in the last week; poo that is unusually large or small and is dry, hard or lumpy; straining or being in pain when you poo; and feeling as though you have not fully emptied your bowels. The NHS does not set a minimum number of these signs, so any of them is worth acting on.

What is the first-line laxative for constipation in the UK?

Bulk-forming laxatives are the BNF first-line recommendation for short-duration constipation where dietary measures have not worked. The BNF lists bran, ispaghula husk (Fybogel), methylcellulose and sterculia (Normacol) in this class. Note that Celevac, the only methylcellulose tablet that was marketed in the UK, is discontinued in the NHS dictionary of medicines and devices, so ispaghula husk and sterculia are the practical choices. They work by increasing stool bulk and water content and must be taken with adequate fluid. Onset of action is up to 72 hours.

This is an educational resource, not a diagnostic tool. For persistent changes in bowel habit, any blood in your stool, unintentional weight loss, or new symptoms that worry you, book an appointment with your GP. In an emergency call 999. This site is not affiliated with the NHS, Bristol Royal Infirmary, Cleveland Clinic, or any medical institution.

Constipation: NHS-Style Guide to Causes, Relief, and When to See a GP

Bristol Stool Types 1-2 - Updated September 2026

What Is Constipation?

The NHS lists the signs of constipation as not having pooed at least three times in the last week, poo that is unusually large or small and is dry, hard or lumpy, straining or being in pain when you go, and feeling as though you have not fully emptied your bowels. There is no threshold number of signs to meet. Constipation is one of the most common digestive complaints in the UK, affecting around one in seven adults at any one time and up to one in three children.

On the Bristol Stool Chart, constipation typically presents as types 1 or 2 - separate hard lumps or a lumpy, hard sausage. Both indicate that stool has spent too long in the colon, losing excess water through the intestinal wall. The result is hard, dry stool that is difficult and uncomfortable to pass.

Common Causes of Constipation

Low fibre intake

Most adults eat about 20g/day vs NHS target of 30g

Inadequate hydration

Dehydration causes the colon to absorb more water from stool

Physical inactivity

Movement stimulates colonic peristalsis

Ignoring the urge

Habitual suppression weakens the natural reflex

Opioid analgesics

Codeine, tramadol, morphine - major cause

Iron supplements

Ferrous sulfate constipates up to 20% of users

Calcium-channel blockers

Used for hypertension and angina

Antacids (aluminium)

Found in some indigestion remedies

Hypothyroidism

Underactive thyroid slows gut motility

IBS-C

Constipation-predominant irritable bowel syndrome

Pregnancy

Hormonal changes + iron supplementation

Pelvic floor dysfunction

Difficulty coordinating muscles for defecation

Self-Care: Fibre, Fluid, and Movement

Dietary Fibre (NHS Target: 30g/day)

The NHS recommends 30g of dietary fibre per day for adults. Most adults eat only about 20g - a significant shortfall. For constipation, soluble fibre is particularly important: it dissolves in water to form a gel-like substance that retains moisture in the stool. Good soluble fibre sources include oats, psyllium husk (available as supplements), ground flaxseed, pulses (lentils, chickpeas, kidney beans), apples, pears, and most root vegetables. Introduce fibre increases gradually over 2-4 weeks to avoid bloating.

Hydration

Aim for 1.5-2 litres of fluid per day. Fibre requires water to work - a high-fibre diet without adequate hydration can actually worsen constipation. Spread your fluid intake through the day rather than drinking large amounts at once. A glass of water first thing in the morning can help stimulate the gastrocolic reflex.

Physical Activity

Regular physical activity accelerates colonic transit. A 30-minute walk per day has been shown in multiple studies to reduce constipation frequency. For desk-based workers, brief movement breaks every 60-90 minutes can make a meaningful difference.

Toileting Position

Elevating your knees above your hips using a toilet stool (placing a small platform under your feet) replicates the physiological squatting position and relaxes the puborectalis muscle, making defecation significantly easier. Several clinical studies have shown this reduces straining and time spent on the toilet.

Laxatives: The NHS Stepwise Approach

1. Bulk-forming (first line)

Examples: Ispaghula husk (Fybogel), sterculia (Normacol)

Taken with plenty of water, they swell in the gut to add bulk and moisture. Results in 2-3 days. Safe for long-term use.

2. Osmotic (second line)

Examples: Macrogol (Movicol, Laxido), lactulose

Draw water into the bowel to soften stool. Macrogol is preferred over lactulose for speed and tolerability. Results in 1-3 days.

3. Stimulant (short-term)

Examples: Senna, bisacodyl

Stimulate colonic muscle contractions. Fast-acting (6-12h). Should not be used long-term without GP advice.

Not suitable as a regular first choice

4. Stool softener

Examples: Docusate sodium

Softens stool by reducing surface tension. Often combined with stimulant laxatives for post-operative constipation.

All laxatives are available without prescription at UK pharmacies. Always take with adequate fluid. Consult your pharmacist before starting a laxative if you are pregnant, have a chronic condition, or are taking regular medications.

When to See Your GP

!No bowel movement for more than 7 days despite dietary change and laxative use
!Blood in or on your stool, or on toilet paper
!Unintentional weight loss alongside a change in bowel habit
!New-onset constipation in a person aged over 50, especially with no obvious dietary explanation
!Abdominal pain, bloating, or vomiting with constipation
!Constipation alternating with diarrhoea (may indicate IBS-M or underlying bowel condition)
!Symptoms suggesting bowel obstruction: vomiting, complete absence of wind and stool, severe abdominal distension
!Family history of bowel cancer and new bowel habit change

For the full NICE suspected bowel cancer referral criteria (NG12, 2-week-wait thresholds), see our Red Flags guide.

Probiotics and Fibre Supplements: What the Evidence Shows

Psyllium husk (sold as Fybogel in the UK) is both a bulk-forming laxative and a prebiotic fibre. It is the most studied dietary supplement for constipation and is recommended by the NHS and NICE. It can improve stool frequency and consistency as effectively as some osmotic laxatives in mild-to-moderate constipation.

For constipation-specific probiotic evidence, Bifidobacterium lactis DN-173010 (found in some commercial probiotic yoghurts) has moderate evidence for reducing transit time in healthy adults with slow transit. Lactobacillus acidophilus NCFM has evidence for bloating reduction. Our partner resource probioticvsprebiotic.com provides a full evidence review.

Sources: NHS UK - Constipation. NICE CG99 (Constipation in children and young people). BNF - Laxative guidance. Lewis SJ, Heaton KW (1997). NICE NG12 - Suspected cancer recognition and referral.

Type 1 (hard lumps)Type 2 (lumpy sausage)IBS-C treatment Red flags

Updated September 2026