Prescribing Laxatives

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Laxatives are used to treat constipation in patients. Prescribing laxatives is a common task for all clinicians and frequently appears in medical school exams and the Prescribing Safety Assessment (PSA).

This article will cover the differentΒ types of laxatives and how to approachΒ prescribing laxatives. Always check and follow local guidelines and refer to the BNF before prescribing.Β 

You might also be interested in our prescribing safety assessment (PSA) question pack, which contains over 500 high-quality PSA questions. We also have a range of prescribing stations in our collection of 1,300 ready-made OSCE StationsΒ πŸ’Š


Constipation is a symptom-based disorder where patients describe problematic defecation because of infrequent stools, hard stools, difficulty passing stools or sensation of incomplete emptying of stool.

In practice, it is often defined as when a patient passes stools less frequently than their normal pattern.1 It is worth noting that many patients define constipation as β€˜hard stool’, with no reference to frequency.

Constipation is more common in the elderly population, and the incidence of constipation is 2-3 times higher in women than in men. The UK primary care cohort study found the prevalence of GP-diagnosed constipation was 12.8/1000 people. However, prevalence is thought to be much higher because people appropriately self-treat using over-the-counter remedies and medications rather than consulting healthcare professionals.1

Constipation rarely causes complications or long-term health problems, and treatment is usually effective, especially when given promptly.2 Chronic constipation is more likely to cause complications and medical emergencies. Complications include faecal loading/impaction, faecal incontinence, haemorrhoids, anal fissures, and rectal bleeding. Emergencies include bowel obstruction and bowel perforation.

Causes of constipation

If a patient presents with constipation, consider the causes of the constipation.

Identifying any associated symptoms (e.g., abdominal pain, weight loss, fatigue) that may indicate a sinister underlying condition such as gastrointestinal malignancy is important. These red-flag symptoms require further investigation, including blood tests and qFIT testing.

The examination of a constipated patient will depend on the clinical context but may include:

  • Abdominal examination: this may assist in identifying the cause of constipation (e.g. deeper abdominal masses); it will also assess for abdominal tenderness and signs of peritonitis
  • Rectal examination: this may identify the causes of constipation (e.g. if there are any fissures or haemorrhoids); it will also assess for hard stool in the rectum
  • Basic observations (vital signs):Β may be useful if assessing an acutely unwell patient with constipation to check for haemodynamic stability or if there are any associated fevers
  • Assessing hydration status: assessing hydration could be helpful when considering if dehydration may be the cause/contribution of constipation

Underlying medical condition

Constipation can be caused by an underlyingΒ medical condition (i.e., secondary constipation). Examples include:

  • Endocrine disorders: hypothyroidism (causing slowed metabolism and reduced peristalsis)
  • Neurological disorders: multiple sclerosis (causing reduced/absent autonomic, sensory and motor responses)
  • Myopathic diseases: myotonic dystrophy (causing muscle weakness/spasm)
  • Structural abnormalities: haemorrhoids, anal fissures (causing pain and stool holding)

Iatrogenic causes

Constipation can be caused by a variety of medications (iatrogenic constipation). Examples include:


Constipation in pregnancy is common and occurs due to the increase in progesterone, which relaxes intestinal smooth muscle.

Psychological causes

Psychological causes of constipation include:

  • Anxiety and depression (causing altered/reduced intake, reduced movement, altered muscle reflexes/sensitivity)
  • Somatisation disorders (causing altered neuromuscular response in the bowel)
  • Eating disorders (from poor intake and/or laxative abuse creating dependence)
Irritable bowel syndrome

Irritable bowel syndrome can cause constipation and recurrent abdominal pain. The Rome IV criteria are used to diagnose IBS.3 The Bristol stool chart can be used to assess stool consistency objectively.

Types of laxative

Laxatives have different modes of action and are not necessarily interchangeable. When prescribing laxatives, it is essential to consider the reason for constipation and choose the appropriate laxative.Β 

In the community, some laxatives can be bought over the counter from pharmacies, and others require a medical prescription.

Bulk-forming laxatives

Examples: ispaghula husk (Fybogel), methylcellulose (Celevac)

Bulk-forming laxatives ‘bulk out’ the stool with soluble fibre. This increases faecal mass and stimulates peristalsis. Their onset of action is up to 72 hours, and common adverse effects include flatulence, bloating and cramping.

Patients should be advised to increase fluid intake when taking bulk-forming laxatives.Β 

Osmotic laxatives

Examples: lactulose, macrogols (Movicol, Laxido)

Osmotic laxatives draw water via osmosis into the stool, making it softer and easier to pass. Adverse effects include abdominal cramps, diarrhoea, nausea and vomiting.

Hepatic encephalopathy

Lactulose is used to treat hepatic encephalopathy as it reduces the intestinal production and absorption of ammonia.

Stimulant laxatives

Examples: senna (Senokot), bisacodyl (Dulcolax), sodium picosulfate

Stimulant laxatives stimulate the nerves of the digestive tract to cause peristalsis.

Stool softening laxatives

Examples: docusate

Stool softening laxatives decrease the surface tension of faecal mass and increase intestinal fluid in the stool.


Glycerol suppositories are both a lubricant and a rectal stimulant.Β 

Prokinetic laxatives are selective serotonin receptor agonists which stimulate intestinal motility. These should only be used underΒ specialist advice.Β 

Prescribing laxatives

Do not prescribe laxatives for patients with suspected bowel obstruction or perforation.

Before advising or prescribing the medical treatment of laxatives, consider lifestyle advice:

  • Increasing calorie intake
  • Body position when passing stool
  • Increased dietary fibre (vegetables, fruit, bran etc)
  • Increased movement and exercise
  • Ensure adequate hydration

Short term constipation

For patients with short-term onset constipation:

Step 1: Start bulk-forming laxative

Step 2: Add or switch to an osmotic laxative

Step 3: Add stimulant laxative

Opioid-induced constipation

For patients with opioid-induced constipation:

Step 1: Start osmotic laxative and stimulant laxative

Step 2: Add softener laxative

Step 3: Naloxegol (mechanism: opioid receptor antagonist)

Faecal impaction4

For patients with faecal impaction (i.e. retention of faeces to the extent that spontaneous evacuation is unlikely), consider oral macrogol/oral stimulant laxative depending on stool consistency.4

If there is an inadequate response to oral laxatives, consider rectal administration of bisacodyl/glycerol.

Chronic constipation

For patients with chronic constipation (constipation symptoms for at least three months):5

Step 1: Start bulk-forming laxative

Step 2: Add or change to osmotic laxative

Step 3: Add stimulant laxative

If at least two laxatives from different classes have been tried, prucalopride can be trialled in women only.

In chronic constipation, always gradually withdraw treatment. In addition, electrolytes should be monitored as there is an increased risk of derangement (e.g. hypokalemia).

Pregnant/breastfeeding women

In pregnant/breastfeeding women– dietary and lifestyle are important to try first, including considering fibre supplements. Bulk-forming laxatives are considered the first line. Always consult the BNF for details if bulk-forming laxatives are not effective.

Common laxatives doses

Examples of common laxative doses include:

  • Ispaghula husk: 1 sachet BD; given in water after food in the morning and evening
  • Lactulose: 15ml BD, adjusted according to response
  • Movicol liquid: 25 mL 1–3 times a day, usually for up to 2 weeks; maintenance 25 mL 1–2 times daily
  • Senna: 7.5mg-15mg OD, usually taken at night; the initial low dose can be gradually increased up to 30mg OD under medical supervision
  • Docusate sodium: 100mg TDS; dose can be increased up to 500mg in divided doses

Always check the BNF before prescribing. Prucalopride, lubiprostone and naloxegol are only prescribed under limited NICE criteria. Linaclotide is used for IBS under specialist guidance.


Dr Seb Pillon

GP and Primary Care Medical Educator


Dr Chris Jefferies


  1. NICE CKS. Constipation – background information. Published in 2023. Available from: [LINK]
  2. NHS Inform. Constipation. Published in 2023. Available from: [LINK]
  3. MDCalc. Rome IV Diagnostic Criteria for Irritable Bowel Syndrome (IBS). Available from: [LINK]
  4. BNF. Constipation | Treatment summaries. Available from: [LINK]
  5. NICE CKS. Constipation – definition. Published in 2023. Available from: [LINK]


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