Constipation / Diarrhoea
Symptoms, Causes & Treatment
Constipation and diarrhoea are among the most common reasons for GP consultation. Most cases are functional and manageable, but persistent changes in bowel habit — especially in adults over 50 — require investigation to exclude serious pathology.
What are Constipation & Diarrhoea?
Bowel habit varies considerably between individuals. Constipation is defined as fewer than 3 bowel movements per week with hard stools and straining. Diarrhoea is defined as loose or watery stools occurring 3 or more times per day. Both have multiple causes ranging from dietary factors and medication to IBD, coeliac disease, and colorectal cancer.
Symptoms of Constipation & Diarrhoea
Bowel habit changes can be subtle or dramatic. The pattern, associated features, and duration guide the assessment.
Fewer than 3 bowel movements per week · Hard or lumpy stools · Straining to pass stools · Feeling of incomplete emptying · Loose watery stools 3+ times per day (diarrhoea) · Urgency to open bowels · Alternating constipation and diarrhoea
Rectal bleeding or blood in stool · Unexplained weight loss with bowel change · Change in bowel habit lasting more than 6 weeks in adults over 50 · Mucus in stool with fever and diarrhoea (possible colitis) · Nocturnal diarrhoea waking from sleep
Rectal bleeding · Change in bowel habit over 50 lasting more than 6 weeks · Unexplained weight loss · Nocturnal diarrhoea — see a GP urgently.
What Causes Constipation & Diarrhoea?
Constipation and diarrhoea arise from functional and organic causes. Red flag features require investigation to exclude serious pathology.
Slow colonic transit — due to inadequate dietary fibre, dehydration, inactivity, and medications (opioids, iron, calcium channel blockers, antidepressants) — is the most common cause of functional constipation.
Infective gastroenteritis from norovirus, rotavirus, Campylobacter, Salmonella, Clostridioides difficile, or E. coli causes acute watery or bloody diarrhoea with cramping. Most resolve within 5–7 days. C. difficile requires specific antibiotic treatment.
IBD (Crohn’s disease and ulcerative colitis) causes chronic bloody diarrhoea, mucus, abdominal pain, and weight loss from autoimmune gut inflammation. Diagnosis is confirmed by colonoscopy and biopsy.
Coeliac disease causes immune-mediated damage to small intestinal villi on exposure to gluten. This causes malabsorption, chronic diarrhoea, weight loss, and fatigue. Treatment is strict lifelong gluten-free diet.
Medications including opioids, codeine, iron, calcium channel blockers, and tricyclic antidepressants cause constipation. Laxatives (lactulose, senna, macrogol, bisacodyl) and stopping the causative drug are the treatments.
Colorectal cancer may present with change in bowel habit, rectal bleeding, weight loss, or iron deficiency anaemia. Any persistent change in bowel habit in adults over 50 requires colonoscopy to exclude malignancy.
Key Risk Factors
Diagnosing Constipation & Diarrhoea
Stool calprotectin, coeliac antibodies, stool culture, and colonoscopy are the key investigations depending on the clinical presentation.
Treatment for Constipation & Diarrhoea
Treatment targets the underlying cause. Laxatives for constipation; ORS and dietary modification for diarrhoea; specific treatment for IBD, coeliac disease, and infection.
Supportive Measures
Increase dietary fibre and fluid. Exercise regularly. Review constipating medications. Use macrogol for constipation. Use ORS sachets for diarrhoea. Keep a food and symptom diary. Warm heat packs ease abdominal cramping with constipation.
Managing Chronic Bowel Conditions
Chronic bowel disorders require long-term management. IBD patients need specialist gastroenterology oversight. IBS patients benefit from dietitian-supervised low-FODMAP diet, CBT, and regular GP review. Bowel cancer screening reduces mortality from colorectal cancer.
When to Seek Help
Bloody diarrhoea with fever and severe dehydration · Suspected bowel obstruction (no bowel movements + vomiting + abdominal distension) — call 999 or attend A&E immediately.
See a GP for any change in bowel habit lasting more than 6 weeks, rectal bleeding, or unexplained weight loss. An online consultation is appropriate for non-urgent bowel symptoms without red flags.
Preventing Constipation & Diarrhoea
Most functional bowel problems are preventable through diet, hydration, exercise, and careful medication management.
Eat at least 25–30g of dietary fibre per day from wholegrain bread, oats, vegetables, fruits, and legumes. Adequate fibre is the single most important prevention for constipation.
Drink 1.5–2 litres of fluid daily. Adequate hydration is essential for bowel transit. Dehydration is one of the most common reversible causes of constipation.
Exercise regularly. Physical activity stimulates colonic motility and significantly reduces the risk of constipation, diverticular disease, and colorectal cancer.
Review all constipating medications with your GP. Opioids, iron supplements, calcium channel blockers, and tricyclic antidepressants all cause constipation. Alternatives or co-prescribing laxatives may be appropriate.
Wash hands thoroughly with soap and water after using the toilet, before preparing food, and after handling raw meat. Most bacterial gastroenteritis and traveller's diarrhoea are preventable with good hand hygiene.
Attend bowel cancer screening (FIT test from age 50+). Any change in bowel habit in adults over 50 lasting more than 6 weeks should be investigated promptly with colonoscopy.
Getting Treatment
A GP can diagnose and manage most causes of constipation and diarrhoea. Red flag symptoms require urgent investigation. Dietitian input for IBS, coeliac disease, and food intolerance is arranged through the GP.
Expert clinical advice, when you need it.
Constipation & Diarrhoea — Frequently Asked Questions
The most common causes of constipation are low dietary fibre, inadequate fluid intake, physical inactivity, and constipating medications (opioids, iron, calcium channel blockers). Secondary causes include hypothyroidism, hypercalcaemia, depression, and bowel cancer. Always exclude red flag causes if constipation is new or persistent in adults over 50.
Persistent constipation can cause anal fissures, haemorrhoids, faecal impaction, overflow incontinence, and rarely, bowel obstruction. Chronic straining is the primary cause of haemorrhoid formation. Long-term unresolved constipation can occasionally mask a more serious underlying pathology.
Seek urgent medical review if you have rectal bleeding, unexplained weight loss, change in bowel habit lasting more than 6 weeks (especially over age 50), nocturnal diarrhoea waking you from sleep, or mucus in the stool with fever. These are red flag symptoms requiring urgent investigation.
Laxatives are safe and effective when used correctly. Osmotic laxatives (macrogol, lactulose) are safe for long-term use in chronic constipation. Stimulant laxatives (senna, bisacodyl) are best used short-term. Never use laxatives if you have unexplained abdominal pain or rectal bleeding without a diagnosis.
Diarrhoea lasting more than 4 weeks is defined as chronic. Common causes include IBS, IBD, coeliac disease, food intolerance, bile acid malabsorption, and microscopic colitis. A GP can arrange stool tests, calprotectin, coeliac antibodies, and colonoscopy to identify the cause.
Coeliac disease is an autoimmune condition triggered by gluten (found in wheat, barley, and rye). It causes villous atrophy in the small intestine, resulting in malabsorption, chronic diarrhoea, bloating, fatigue, and iron deficiency anaemia. It is diagnosed by blood test (anti-TTG IgA) and duodenal biopsy. The only treatment is a strict lifelong gluten-free diet.
IBD (Crohn's disease and ulcerative colitis) and IBS are distinct conditions. IBD causes measurable gut inflammation visible on colonoscopy and blood tests. IBS is a functional disorder with no structural or inflammatory abnormality. A stool calprotectin test reliably distinguishes the two in most cases.
A GP can diagnose most causes of constipation and diarrhoea. Red flag symptoms require same-day or urgent review. Blood tests, stool calprotectin, coeliac antibodies, and referral for colonoscopy can all be arranged in primary care. Online GP consultations are appropriate for non-urgent bowel symptom assessment.