BMA Concise Guide to Medicine & Drugs


Brand names Duphalac, Lactugal

Used in the following combined preparations None


Drug group Laxative

Overdose danger rating Low

Dependence rating Low

Prescription needed No

Available as generic Yes


Lactulose is an effective laxative that softens faeces by increasing the amount of water in the large intestine. It is used for the relief of constipation and faecal impaction, especially in the elderly. This drug is less likely than some of the other laxatives to disrupt normal bowel action.

Lactulose is also used for preventing and treating brain disturbance associated with liver failure, a condition known as hepatic encephalopathy.

Because lactulose acts locally in the large intestine and is not absorbed into the body, it is safer than many other laxatives. However, the drug can cause stomach cramps and flatulence especially at the start of treatment.


Follow instructions on the label. Call your doctor if symptoms worsen.

How taken/used Liquid.

Frequency and timing of doses 2 x daily (chronic constipation); 3–4 x daily (liver failure).

Adult dosage range 15–30ml daily (chronic constipation); 90–150ml daily (liver failure).

Onset of effect 24–48 hours.

Duration of action 6–18 hours.

Diet advice It is important to maintain an adequate intake of fluid – up to 8 glasses of water daily.

Storage Keep in original container at room temperature out of the reach of children. Do not store after diluting. Do not refrigerate or freeze.

Missed dose Take as soon as you remember. If your next dose is due within 3 hours, take a single dose now and skip the next.

Stopping the drug In the treatment of constipation, the drug can be safely stopped as soon as you no longer need it.

Exceeding the dose An occasional unintentional extra dose is unlikely to be a cause for concern. But if you notice any unusual symptoms, or if a large overdose has been taken, notify your doctor.


Adverse effects are rarely serious and often disappear when your body adjusts to the drug. The adverse effects include flatulence, belching, stomach cramps, nausea, vomiting, and abdominal distension. Consult your doctor if these are severe. If diarrhoea occurs, this may indicate that the dosage is too high and needs to be adjusted; consult your doctor.


Anticoagulants Lactulose may increase the anticoagulant effect of warfarin.


Be sure to consult your doctor or pharmacist before taking this drug if:

· You have severe abdominal pain.

· You have diabetes.

· You suffer from lactose intolerance or galactosaemia.

· You are taking other medicines.

Pregnancy No evidence of risk. Discuss with your doctor.

Breast-feeding No evidence of risk.

Infants and children Reduced dose necessary.

Over 60 No special problems.

Driving and hazardous work No known problems.

Alcohol No known problems.


In children, prolonged use may contribute to the development of dental caries.