What are the potential side effects of common laxatives, and how can I counsel patients on their safe use?

Guideline-aligned answer with reasoning, red flags and references. Clinically reviewed by Dr Kola Tytler MBBS CertHE MBA MRCGP.

Posted: 14 August 2025 Guideline-Aligned (High Confidence) Clinically Reviewed
Dr Kola Tytler MBBS CertHE MBA MRCGPClinical Lead • iatroX

Potential Side Effects of Common Laxatives

  • Bulk-forming laxatives (e.g., ispaghula): These may cause abdominal colic and, rarely, bowel obstruction . Inadequate fluid intake with these laxatives can lead to intestinal obstruction, which may occur quickly if there is already a partial obstruction ,. Unprocessed bran, a type of fibre, can cause bloating and flatulence and reduce the absorption of micronutrients . Bulk-forming laxatives are generally less useful in palliative care due to their unpalatable consistency and the large fluid intake required, making them unacceptable to many ill individuals .
  • Osmotic laxatives (e.g., lactulose, macrogol, sorbitol): Lactulose and sorbitol may produce gas and contribute to abdominal distension and discomfort . Sorbitol, an artificial sweetener, should be avoided by people with diarrhoea . Lactulose is generally discouraged for constipation in people with Irritable Bowel Syndrome (IBS) .
  • Stimulant laxatives (e.g., bisacodyl, senna, sodium picosulfate): Senna may cause diarrhoea and abdominal cramps, although this has not been confirmed as an issue in controlled trials in breastfed infants .
  • Phosphate enemas: These can sometimes cause water and electrolyte disturbances, particularly in people aged 65 years or older and those with comorbidities .
  • Paraffin: This is not recommended due to a risk of lipoid pneumonia if aspirated .
  • General in Pregnancy: While most laxatives have minimal systemic absorption and are commonly used during pregnancy, they should only be used for short periods if needed, as they may induce electrolyte imbalance . No adverse fetal effects have been reported following the use of bulk-forming laxatives during pregnancy . There is very limited data on senna and docusate in pregnancy, suggesting no increased risk of congenital malformations .

Counselling Patients on Safe Use

  • Lifestyle Measures (First-line): Advise patients to increase dietary fibre, ensure adequate fluid intake, and increase activity levels ,. For adults with hard stools or clinical dehydration, encourage a fluid intake of at least 1.5 litres per day, unless contraindicated . For children, a balanced diet should include adequate fluid and fibre from sources like fruit, vegetables, high-fibre bread, baked beans, and wholegrain breakfast cereals . Daily physical activity tailored to the child's development should also be encouraged . Dietary interventions alone should not be used as first-line treatment for idiopathic constipation in children .
  • Laxative Administration: If lifestyle measures are ineffective, offer short-term oral laxative treatment . Adjust the dose, choice, and combination of laxatives based on the patient's symptoms, desired speed of relief, response to treatment, and personal preference . The aim is to achieve a soft, well-formed stool (Bristol Stool Form Scale type 4) .
  • Stepped Approach: Offer a bulk-forming laxative first-line, such as ispaghula . If stools remain hard or difficult to pass, add or switch to an osmotic laxative like macrogol or lactulose . If stools are soft but difficult to pass or there is a sensation of inadequate emptying, consider a short course of a stimulant laxative such as bisacodyl or senna .
  • Specific Patient Groups:
    • Pregnancy: Most laxatives are commonly used and have minimal systemic absorption; if needed, use for short periods .
    • Breastfeeding: Various laxatives can be used short-term when breastfeeding infants one month of age or older . Bulk-forming, osmotic, bisacodyl, sodium picosulfate, docusate, and glycerol suppositories are considered compatible or safe . Senna's active ingredient is undetectable in breast milk . If there is uncertainty about laxative use or safety during breastfeeding, contact the UK Drugs in Lactation Advisory Service (UKDILAS) .
    • Opioid-induced Constipation: Do not prescribe bulk-forming laxatives . Offer an osmotic laxative and a stimulant laxative, or docusate as an alternative . In palliative care, a combination of a stimulant with a softening laxative is effective for opioid-induced constipation .
    • Palliative Care: Avoid bulk-forming laxatives, phosphate enemas (if possible), and paraffin . Seek specialist advice if constipation persists despite measures .
    • Children: Continue laxative medication at a maintenance dose for several weeks after a regular bowel habit is established, which may take several months . Do not stop medication abruptly; gradually reduce the dose over months in response to stool consistency and frequency . Provide detailed, evidence-based information about their condition, how to take medication, what to expect, and the importance of continuing treatment .
  • When to Avoid/Seek Advice: Identify and manage any underlying secondary causes of constipation or drug treatments contributing to symptoms . Do not carry out rectal interventions (enemas, suppositories, or manual evacuation) in people who are neutropenic (e.g., on chemotherapy), have thrombocytopenia, or have rectal or anal disease .

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