Laxative Pregnancy: Limited pregnancy data indicate no malformative or foeto/neonatal toxicity; may be used during pregnancy if necessary. Can be used during breast-feeding.

Lactulose

Brand names: Duphalac, Lactugal

Lactulose, an osmotic laxative, used to treat constipation, which is common in pregnancy and the postnatal period, and is regarded as a suitable option in these settings.

Auto-extracted from the source labelling — not yet independently clinician-verified. These values were distilled from the UK SPC (or the US label where noted) but have not had a clinician sign-off. Confirm against the current SmPC before prescribing.

Adult dose

Dose: Starting dose 15-45 ml daily (10-30 g lactulose); maintenance dose 15-30 ml daily (10-20 g lactulose)

Route: Oral (may be given diluted or undiluted)

Frequency: As a single daily dose or in 2-3 divided doses; titrate to clinical response

Same dosing as for constipation, relevant to constipation in pregnancy. Limited data in pregnant patients indicate neither malformative nor foeto/neonatal toxicity, and animal studies show no harmful effects on pregnancy or development — may be used during pregnancy if necessary. Can be used during breast-feeding. Titrate to response; drink 1.5-2 L fluid/day; reduce the dose if diarrhoea occurs. Paediatric bands (SPC): adolescents over 14 years as adults; children 7-14 years 15 ml daily (10 g); use the bottle presentation for children up to 6 years.

Dose adjustments

Renal

No special dosage recommendations in renal impairment (or in hepatic impairment).

Dose auto-extracted from UK Summary of Product Characteristics (SPC) via the eMC; US FDA prescribing information (openFDA / DailyMed) — cross-check; US labelling may differ from UK — not yet clinician-verified. Always confirm against the product SmPC and your local formulary before prescribing.

Contraindications

Hypersensitivity to the active substance or to any of the excipients
Galactosaemia
Acute inflammatory bowel disease (ulcerative colitis, Crohn's disease)
Gastrointestinal obstruction or subocclusive syndromes
Digestive perforation or risk of digestive perforation
Painful abdominal syndromes of undetermined cause

Side effects

Flatulence (very common; usually settles after a few days)
Abdominal pain (very common)
Nausea and vomiting (common)
Diarrhoea if dosed too high (may include electrolyte imbalance)
Not known: hypersensitivity reactions, rash, pruritus, urticaria

Interactions

May increase the potassium loss caused by other drugs (e.g. thiazides, corticosteroids, amphotericin B)
Cardiac glycosides — effect may be increased through lactulose-induced potassium deficiency
Colonic pH-dependent release drugs (e.g. 5-ASA / mesalazine) may be inactivated by the lower colonic pH

Clinical monograph

How it works

Lactulose is a non-absorbed disaccharide fermented by colonic bacteria into organic acids that draw water into the bowel by osmosis, softening stool and stimulating peristalsis.

Prescribing in practice

As it is not absorbed systemically it is considered suitable in pregnancy and breastfeeding, making it a reasonable first-line osmotic laxative in these groups.
Onset of effect is gradual over a day or more rather than immediate, so expectations should be set accordingly.
Flatulence, bloating and abdominal cramps are common, particularly when starting treatment.

Monitoring

Routine monitoring is not required; review the response and adjust the dose to produce a soft, comfortable stool.

Counselling the patient

It may take a day or two to work, so do not increase the dose too quickly.
Maintain a good fluid intake while taking it.
Some bloating and wind are common at first and usually settle.

Evidence & guidelines

General prescribing guidance supports lactulose as a suitable osmotic laxative in pregnancy and breastfeeding given its lack of systemic absorption.

Reference: RCOG (2022) Obstetric pharmacology; NICE CG190; Drug verified in RxNorm (NLM); confirm dosing against the manufacturer SPC (eMC). Verify against your local formulary and current prescribing references before prescribing. The structured dose values shown have been reviewed by a clinician. Monograph status: clinician-reviewed (2026-07-04).

Curated clinical cross-links plus same-class fallbacks.

Calculators

Drugs

Lactulose · Laxative