Duphalac (Lactulose): Constipation Uses, Safety and Precautions

What is Duphalac syrup?

Duphalac contains lactulose, an osmotic laxative that helps retain water in the bowel and softens stools. The reviewed UK oral solution contains 3.335 g per 5 ml, equivalent to 667 mg/ml. This matches the concentration of the syrup discussed here.

The product is used for constipation and, under a separate medical treatment plan, hepatic encephalopathy associated with liver disease. These are different indications with different treatment goals.

What should patients expect?

Lactulose may take two or three days to work. Lack of an immediate bowel movement does not by itself justify repeated extra doses. Use the supplied measuring device rather than a kitchen spoon and follow the actual product instructions. Fluid intake is important, but people with a prescribed fluid restriction should discuss their individual needs.

NHS information recommends seeking advice if constipation has not improved or has worsened after several days. New unexplained abdominal pain should be evaluated before starting treatment. Persistent changes in bowel habit need assessment rather than indefinite laxative use without review.

Side effects and situations requiring care

Gas and bloating are common at first. Stomach discomfort, nausea, vomiting and diarrhoea can also occur. Frequent or prolonged diarrhoea can cause dehydration and electrolyte loss, including low potassium. Marked weakness, muscle problems, palpitations, dizziness or ongoing vomiting need prompt assessment. Breathing difficulty or swelling suggesting anaphylaxis requires emergency help.

The UK label excludes use in galactosaemia and gastrointestinal obstruction, perforation or risk of perforation. Residual sugars from manufacture matter for certain inherited sugar intolerances. Discuss diabetes, lactose intolerance and the exact formulation with a pharmacist; higher encephalopathy regimens may have different implications for blood glucose.

Interactions, pregnancy and breastfeeding

The cited UK label states that interaction studies have not been performed. This is not proof that every combination is safe. Give the pharmacist a complete list of medicines and other laxatives, particularly if diarrhoea develops or a medicine requires stable fluid and electrolyte levels.

Because lactulose is poorly absorbed, the UK product information permits use during pregnancy and breastfeeding; NHS advice still recommends checking personal suitability. Children should receive laxative treatment under appropriate professional supervision. This page does not set an individual treatment dose or duration.

Sources

• Duphalac 3.335 g/5 ml Oral Solution — UK SmPC — Text revised April 2022; emc updated 13 June 2022
• NHS — Lactulose — Reviewed 8 September 2026

Source check: 30 October 2026. This records a check of the cited sources, not a clinical review by a doctor or pharmacist. Product instructions and approved uses can differ between countries. Follow the leaflet supplied with your medicine and obtain personal advice from a qualified healthcare professional.