Constipation
Red Flags
| Red flag | Why dangerous | Action |
|---|---|---|
| Rectal bleeding (with pain or weight loss under 50; any at 50+) | NICE NG12: colorectal cancer until proven otherwise — do not assume haemorrhoids without investigation in this age group | FIT; suspected cancer pathway referral if ≥10 µg Hb/g |
| Change in bowel habit (any age), or weight loss + abdominal pain at 40+ | NICE NG12 FIT criterion (suspected cancer pathway referral if FIT ≥10 µg Hb/g) — malignancy, lymphoma, malabsorption, systemic illness | FIT; suspected cancer pathway referral if ≥10 µg Hb/g |
| Absolute constipation + no flatus + distension + vomiting | Large bowel obstruction — surgical emergency; perforation risk if laxatives given | 999 / A&E |
| New bowel + bladder dysfunction + leg symptoms | Cauda equina syndrome — neurosurgical emergency; MRI spine within hours | 999 |
| Iron-deficiency anaemia (any age) | NICE NG12: right-sided colonic malignancy commonly presents with IDA only; FIT under NG12, and upper and lower GI investigation (BSG 2021) | FIT; suspected cancer pathway referral if ≥10 µg Hb/g |
- Not asking about rectal bleeding — the single most important red flag in any bowel presentation
- Not asking about drug causes — opioids and iron are extremely common causes; missing them prevents the simplest fix
- Not acknowledging the embarrassment of the topic — closes the consultation environment
- Cancer fear not explored in ICE — leaves patient anxious throughout; undermines management engagement
999 or Same-Day / suspected cancer pathway referral
Act now- Large bowel obstructionNo flatus + distension + vomiting → 999 surgical emergency; do not give laxatives
- Cauda equina syndromeBowel/bladder change + leg symptoms → 999 emergency MRI; not functional constipation
- FIT: bleeding, weight loss or bowel changeNICE NG12 → colorectal suspected cancer pathway referral if FIT ≥10 µg Hb/g; do not delay with laxative trial first
- IDA at any ageFIT (NICE NG12) → suspected cancer pathway referral if ≥10 µg Hb/g; men and post-menopausal women also need upper and lower GI investigation (BSG 2021) + iron replacement
- Palpable abdominal or rectal massRectal mass → suspected cancer pathway referral without FIT; abdominal mass → FIT plus urgent imaging (NICE NG12)
Same-Day / Days
Days- Faecal impactionSevere pain, unable to open bowels >7 days, hard mass on DRE → macrogol disimpaction regimen; if no response 48h → phosphate enema
- Suspected secondary cause (hypothyroidism, hypercalcaemia)New constipation + systemic symptoms → urgent TFTs + calcium before laxative treatment
- Constipation in known malignancyOIC or tumour effect → specialist palliative care bowel regime; naloxegol if OIC
Primary Care Management
GP practice- Functional constipation (Rome IV, no red flags)Lifestyle → ispaghula → macrogol ± stimulant; review at 2–4 weeks
- Drug-induced (opioids, iron, CCBs)Stop or switch drug; macrogol + bisacodyl for OIC from day 1; 4-week review
- IBS-CLow-FODMAP diet; macrogol; linaclotide if failed 12 months first-line
- Constipation in pregnancyIspaghula husk + lactulose; avoid bisacodyl 1st trimester
- Prescribing laxatives without documented red flag screen — medico-legally risky
- Not offering FIT for rectal bleeding, weight loss, IDA or a change in bowel habit
- Treating obstruction as constipation — risk of perforation if laxatives given
- Not offering DRE where it would change management (new, unexplained or refractory constipation, suspected impaction, bleeding or mass)
- DRE performed without explaining it and checking consent — dignity and consent failure
- Not weighing the patient when bowel symptoms are the presentation
- Ordering routine AXR for uncomplicated constipation — not indicated
- Not checking TFTs/calcium when the history suggests a secondary cause (bloods are by context, not routine)
- Ordering colonoscopy without NICE NG12 criteria being met
"The codeine you're taking for your back is causing most of this constipation. Pain medications like codeine work by switching off pain signals in the brain — but they also switch off the signals that keep the bowel moving. Think of your bowel as having its own nervous system with a conveyor belt that normally keeps things moving along. Codeine slows that conveyor belt right down. This is completely treatable — and importantly, it's not a sign of anything more serious. I've specifically checked for the warning signs that would concern me, and none of those are present. What I want to do is prescribe something that works alongside the codeine to keep things moving."
"Could this be bowel cancer?"
"That's really important to address. I've asked you specifically about blood in your stool and about weight loss — those are the two things that would concern me most, and both of those are absent. You also have a very clear drug cause in the codeine. Based on everything you've told me, I'm reassured this is the codeine causing the problem. That said, if at any point you develop any bleeding or lose weight without trying, I want you to come back immediately — that would completely change my approach. Does that feel clear?"
Functional constipation (Rome IV)
≥2 features for ≥3 months: straining, hard stools, incomplete evacuation, <3/week, manual manoeuvres, sensation of blockage. No red flags. Lifestyle → ispaghula (bulk-forming) → macrogol ± stimulant.
Drug-induced constipation
Opioids, iron, CCBs (verapamil), TCAs, anticholinergics, antacids. Identify and modify. Macrogol + bisacodyl for OIC from day 1 of opioid.
IBS with constipation (IBS-C)
Abdominal pain ≥1 day/week for 3 months, associated with bowel change, relieved or worsened by defaecation. Low-FODMAP + targeted pharmacotherapy. Linaclotide if failed 12 months.
Hypothyroidism
TSH elevated. Treat with levothyroxine. Constipation often resolves without laxatives once thyroid is adequately treated. Most commonly missed secondary cause.
Pelvic floor dyssynergia
Straining, digitation, incomplete evacuation. Confirmed by specialist anorectal physiology (balloon expulsion, manometry) — not by DRE alone. Laxatives ineffective. Biofeedback is the primary treatment.
Coeliac disease
Anti-tTG positive + bowel symptoms + bloating. May mimic IBS-C. Gluten-free diet resolves symptoms. Always exclude before diagnosing IBS-C.
Colorectal cancer
Red flags: bleeding, bowel change, weight loss or IDA → FIT, suspected cancer pathway referral if ≥10 µg Hb/g; rectal mass → suspected cancer pathway referral. Do not manage as functional without investigation.
Large bowel obstruction
No flatus + distension + vomiting. 999 surgical emergency. Never give laxatives if obstruction suspected.
- Not directly addressing the cancer fear — patient leaves still anxious
- Using jargon without explanation
- Not checking understanding after sharing the diagnosis
- Referring to gastroenterology at first presentation without primary care management trial
- Not applying suspected cancer pathway referral when red flags indicate colonoscopy is warranted
Adequate fluid softens stool. Fibre absorbs water — insufficient fluid makes high-fibre foods worsen constipation. Fluid must be addressed before fibre is increased.
Carry a water bottle; replace coffee/tea with water; aim for pale yellow urine; start the day with a glass of water before caffeine.
Insoluble fibre (vegetables, wheat bran) provides bulk. Soluble fibre (oats, pulses, fruit) feeds gut microbiome and promotes peristalsis. Sudden large increases cause bloating — gradual is essential.
Kiwi fruit has specific RCT evidence — 2 kiwis/day. Linseeds (1 tbsp/day): cheap and effective. Oats, lentils, tinned beans. Brown bread. Gradual increase over 2–3 weeks.
Suppressing the defaecation urge raises the threshold for the next urge — worsening constipation progressively. Optimal posture (knees above hips, leaning forward) straightens the anorectal angle and may make evacuation easier; no specific footstool height is evidence-based.
Respond to urge immediately. Use a footstool to raise knees. Sit on the toilet 20–30 min after breakfast (gastrocolic reflex) and allow time — do not rush. Restricted toilet access at work — encourage discussion with employer.
Physical activity directly stimulates colonic peristalsis and increases parasympathetic nervous activity. Regular activity as able is a practical supportive measure.
Daily walking is most sustainable. Activity after meals exploits the gastrocolic reflex. Frame as therapeutic not cosmetic — the mechanism resonates with patients.
Drug-induced constipation is the most reversible cause. Not all drugs can be stopped, but all can be reviewed.
Opioids: cannot stop — add laxative. Iron: try ferrous fumarate or alternate-day; IV iron if oral not tolerated. CCBs: switch to amlodipine. TCAs: switch to SSRI if depression. Aluminium antacids: switch to PPI.
Chronic stress activates the sympathetic nervous system, reducing colonic motility. The gut-brain axis is bidirectional — constipation worsens anxiety and anxiety worsens constipation.
PHQ-9/GAD-7 where low mood or anxiety is suggested (and in IBS). NHS Talking Therapies referral for CBT if anxiety or depression identified. Hypnotherapy, CBT or psychological therapy: consider referral if IBS has not responded to drug treatment after 12 months (refractory IBS, NICE CG61).
Macrogol (Movicol/Laxido) — 1–2 sachets daily in water
- Preferred osmotic in practice — after ispaghula in functional constipation; first choice (with a stimulant) in opioid-induced constipation
- Draws water into bowel by osmosis — softens and bulks stool
- No tachyphylaxis; safe long-term; safe in pregnancy
- Disimpaction: 4 sachets twice daily (8/day) for up to 3 days
- Review at 4 weeks; if inadequate, add bisacodyl
Bisacodyl 5–10 mg nocte OR Senna 7.5–15 mg (1–2 tabs) nocte (add to macrogol)
- Activates enteric nerves → stimulates peristalsis; onset 8–12 hours
- Add to macrogol (not replace) if osmotic alone insufficient after 2–4 weeks
- For OIC: macrogol + bisacodyl from day 1 of opioid — do not wait
- Bisacodyl preferred over senna in elderly (gentler action)
- Start with 5 mg bisacodyl; increase to 10 mg if needed
- Prucalopride 2 mg OD: Women with chronic constipation; ≥2 laxatives from different classes at highest tolerated doses for ≥6 months have failed and invasive treatment is being considered (NICE TA211)
- Naloxegol 12.5–25 mg OD: OIC with inadequate response to laxatives (NICE TA345: at least moderate symptoms despite ≥1 laxative class for ≥4 days in the prior 2 weeks); peripheral mu-receptor antagonist — does not affect central analgesia
- Linaclotide 290 mcg OD: IBS-C only (not functional constipation); optimal or maximum tolerated doses of laxatives from different classes have not helped and constipation for ≥12 months (NICE CG61)
- Opioid-induced constipation — macrogol + bisacodyl from day 1; do not start bulk-forming
- Faecal impaction — high-dose macrogol disimpaction regimen
- Pregnancy — ispaghula + lactulose; avoid bisacodyl 1st trimester
- IBS-C — low-FODMAP + macrogol; linaclotide if failed 12 months
- Chronic functional constipation — macrogol 1–2/day
- Anal fissure — macrogol + topical GTN 0.4%
"These sachets draw water into the bowel to soften your stool — take each one in a large glass of water. Give it 2–3 days for the first effect, but at least a week to properly settle. The target is a stool that's soft and formed — not hard, not runny."
In SCA: macrogol as first-line (not lactulose) demonstrates current prescribing knowledge — a specific Tasks mark. For faecal impaction: "disimpaction regimen" — 8 sachets/day (4 twice daily) for up to 3 days — is a specific clinical knowledge point.
"Take this tablet at night — it stimulates the bowel to move, so you'd usually go in the morning. It works alongside the macrogol sachets; the two together are much more effective for your type of constipation than either one alone."
In SCA: bisacodyl should be started on day 1 of opioid therapy alongside macrogol — NOT waited until constipation develops. This proactive approach demonstrates specific OIC knowledge and gains a Tasks mark.
"Take two tablets at night — the bowel usually moves 8–12 hours later. Your urine may turn slightly darker — that's harmless. Start with two tablets and increase if needed."
"This medication specifically blocks the effect of the codeine on your bowel — without affecting the pain relief you get from it. Take on an empty stomach. It may cause cramping initially — that's the system getting moving again."
In SCA: naloxegol mechanism (peripheral mu-receptor antagonist, does not affect central analgesia) is a specific clinical knowledge point. NICE TA345 criteria: OIC with inadequate response to laxatives (≥1 laxative class for ≥4 days in the prior 2 weeks).
"This tablet works on a specific receptor in the bowel — think of it as pressing the accelerator for your bowel's own movement. Take it in the morning; the most common side effect is a headache for the first few days, which usually passes."
In SCA: prucalopride requires NICE TA211 criteria documentation — ≥2 laxative classes failed at highest tolerated doses for ≥6 months, invasive treatment being considered, in a woman. Knowing the criteria gains a Tasks mark.
"This capsule works specifically for IBS with constipation — it increases bowel fluid and also helps with the abdominal pain. Take it 30 minutes before your first meal. Diarrhoea is common in the first week — usually settles."
In SCA: linaclotide = IBS-C only, not functional constipation; NICE CG61 criteria = laxatives from different classes failed and constipation for ≥12 months. Prescribing it for functional constipation without abdominal pain would be incorrect.
4 weeks — Laxative response assessment
Review BSS, frequency (≥3/week target?), straining, bloating. If macrogol + lifestyle adequate: continue. If inadequate: add bisacodyl 5 mg nocte. Review blood test results (TFTs, calcium). Re-assess drug causes — has offending medication been modified? Rescreen red flags.
8–12 weeks — Sustained response or escalation
If macrogol + bisacodyl achieving BSS 3–5: reassess whether lifestyle is now sufficient. If IBS-C and inadequate response: low-FODMAP dietitian referral; PHQ-9 + GAD-7 for mood. If refractory: document treatments tried for referral letter.
6 months — Specialist referral decision
Refer by clinical need, not a fixed 6-month wait (severe symptoms, recurrent impaction, suspected defaecatory dysfunction, neurological disease, nutritional impact): gastroenterology for transit studies and/or anorectal manometry. Women: if NICE TA211 criteria are met, document them — prucalopride is prescribed by a clinician experienced in chronic constipation. Review opioid — can dose be reduced or agent switched?
Annual — Chronic constipation review
Document current stool pattern and laxative dose. Review drug causes. Check TFTs and calcium only if the history suggests a secondary cause. Rescreen for red flags at every annual review — cancer risk increases with age. Apply suspected cancer pathway referral if any red flag develops.
Each opioid prescription — OIC review
Every opioid prescription review must include an explicit bowel habit assessment. If macrogol + bisacodyl not achieving BSS 3–5: escalate to naloxegol (NICE TA345). If opioid dose increased: increase laxative dose proportionally. Document bowel regime in opioid review.
⚠ Three scenario-specific safety-net phrases
- Lactulose chosen for OIC — may cause bloating and is less suitable in opioid-induced constipation
- OIC managed with lifestyle advice alone — insufficient for opioid bowel dysfunction
- No red flag safety-net for rectal bleeding and weight loss — medico-legal critical omission
- DRE not offered or discussed when it would change management
- Cancer fear not directly resolved
- Closing question absent
- Red flags screened: no bleeding, no weight loss documented
- Drug cause identified (codeine) and managed (macrogol + bisacodyl)
- Macrogol as first-line (not lactulose)
- Bisacodyl added for OIC from first prescription
- Red flag safety-net: bleeding/weight loss = immediate return + suspected cancer pathway referral
- Obstruction emergency safety-net given
- 4-week follow-up booked
- Embarrassment acknowledged early and explicitly
- Cancer fear named and directly resolved with red flag screen reference
- Conveyor belt analogy used for mechanism
- Understanding checked during explanation
- Quality of life impact acknowledged
- Closing question asked
Who you are
Linda Patel, 52 years old, office administrator. Opening bowels every 3–4 days with hard, lumpy stools requiring significant straining. Has had this since starting codeine phosphate 30 mg QDS for chronic lower back pain (prescribed 7 months ago). Tried Fybogel OTC — minimal improvement. Tried Senna for 5 days — temporary improvement then back to normal. Drinks 5–6 cups of coffee/tea daily, very little water. Sedentary office job. Low-fibre diet. No rectal bleeding. No weight loss. No family history of bowel cancer she knows of. Takes amlodipine 5 mg for hypertension. BMI 27.
Hidden agenda
Worried it might be bowel cancer — her aunt was diagnosed with bowel cancer last year. She has not mentioned this to anyone. She will not volunteer the cancer fear unless specifically asked about concerns. If the GP directly asks "is there something you're worried this might be?" she will disclose it. If the GP then addresses it with the specific red flag screen ("no blood, no weight loss, and a clear drug cause"), she becomes significantly calmer and much more engaged with the management plan.
Symptoms if asked directly
- Stool frequency: every 3–4 days (was daily before codeine)
- Stool consistency: BSS type 1–2; significant straining
- No blood in stool, no blood on paper
- No unintentional weight loss; weight stable
- Significant afternoon bloating
- No abdominal pain that comes before opening bowels
- Holds on at work — toilets are shared and not private
Bonus details
- If asked about holding the urge at work: "Yes — I hold it until I get home because the toilets aren't very private" (opens toilet habit advice)
- If asked fluid intake: mainly 5–6 coffees, maybe 1–2 glasses water
- Does not consider supplements a "medication" — won't volunteer Fybogel unless asked specifically about OTC preparations
Resolution criteria: Linda will be satisfied if the candidate (1) acknowledges embarrassment; (2) directly addresses the cancer fear with red flag screen reference ("no blood, no weight loss, clear drug cause"); (3) explains the codeine mechanism with conveyor belt analogy; (4) prescribes macrogol + bisacodyl and stops the Fybogel (bulk-forming is not used in opioid-induced constipation); (5) gives specific lifestyle advice (fluid, toilet habit); (6) gives specific red flag safety-net ("come back immediately if bleeding or weight loss").
→ Single most important red flag in any bowel presentation
→ Macrogol is the preferred first-line osmotic; lactulose causes bloating, is slower
→ Requires macrogol + bisacodyl from day 1 of opioid
→ Must name and resolve with specific red flag screen reference
→ Offer where it changes management; always with explanation, consent and chaperone
→ Name bleeding and weight loss specifically as immediate return triggers
→ Not indicated for uncomplicated constipation
→ Exclude impaction first; add an osmotic for hard stools; stimulant alone suits soft stools with difficult evacuation
→ Always end with "Is there anything else on your mind?"