Lactulose
Pronunciation: LAK-tyoo-lose.
- Generic name
- lactulose
- Brand names
- Duphalac, Lactugal (United Kingdom)
- Drug class
- Osmotic laxative (synthetic disaccharide)
- Form
- Oral solution
- Route
- Oral
- Legal status
- Availability varies by country and product; both prescription and over-the-counter presentations exist.
Availability and supply rules vary by country
Trade names by country: United States · Canada
Australia: · Full directory
What lactulose is and how it works
Lactulose is a synthetic sugar that is not absorbed in the small intestine; in the colon it draws water into the bowel (a laxative effect) and, at higher doses, helps reduce blood ammonia in people with liver disease. (1)
It is used at a lower dose for constipation and at a much higher dose to prevent or treat hepatic encephalopathy (confusion related to liver disease). Follow the dose intended for your specific condition.
Mechanism of action: how lactulose works
Lactulose passes largely unchanged to the colon, where bacterial metabolism produces low-molecular-weight organic acids that acidify colonic contents; this osmotic effect draws water into the bowel and, in hepatic encephalopathy, reduces blood ammonia by an estimated 25-50%, correlating with improvement in mental state and EEG patterns. (1)
What lactulose is used for
Constipation
Used to relieve constipation by increasing water content and softening stool. (2)
Hepatic encephalopathy
Used at a higher dose to prevent and treat portal-systemic (hepatic) encephalopathy, including pre-coma and coma stages, in people with significant liver disease. It works partly by reducing blood ammonia levels. (1) (2)
Before taking lactulose
Do not take / not appropriate for
- Do not take lactulose if you require a low-galactose diet, since this product contains a small amount of galactose. (all products) (1)
Tell your clinician about
- Diabetes, since this product contains galactose and lactose.
- Any significant liver disease.
- Whether you are due to have a bowel procedure such as a colonoscopy or proctoscopy involving electrocautery (heat/spark-based instruments).
- Every other medicine you take, especially neomycin or other antibiotics, or antacids.
- Pregnancy or breastfeeding.
How to take lactulose
- Take exactly as directed on the product label or by your prescriber for your specific condition.
- Use the measuring device supplied with the product rather than a kitchen spoon.
- Can be taken with or without food; you may dilute it with water or juice.
- Drink plenty of fluids while taking lactulose.
- Do not take other laxatives at the same time, especially when starting treatment, unless your prescriber advises it.
- If you are having a bowel procedure involving electrocautery, tell the team you take lactulose beforehand, since it can produce gas that poses a fire/explosion risk with these instruments unless proper bowel preparation is used.
Procedures and treatment changes
Tell the treating team before surgery, procedures, or any medicine change. Do not alter treatment without the responsible clinician. (1) (2)
Missed dose
Skip the missed dose and continue your regular schedule. Do not take a double dose to make up for a missed one.
Overdose
Contact your prescriber, pharmacist, or a poison-control/emergency service if a significant overdose is suspected. Excessive doses can cause diarrhoea with dehydration and electrolyte imbalance, which need medical assessment. (1)
Side effects
Digestive symptoms like gas and cramping are common, especially when starting treatment, and usually improve over time.
Bloating, wind, belching, or stomach cramps
What to notice: Reported in around 1 in 5 people, especially at the start of treatment.
What to do: Tell your prescriber or pharmacist if severe or persistent. (1)
Nausea or vomiting
What to notice: Can occur, particularly at higher doses.
What to do: Tell your prescriber if troublesome. (1)
Signs of dehydration or electrolyte imbalance
What to notice: Watery diarrhoea, muscle weakness, or an irregular heartbeat, especially after an excessive dose.
What to do: Contact your prescriber promptly; a clinician will decide whether the dose needs to be adjusted or the medicine stopped. (1)
Serious warnings
Fire/explosion risk during bowel procedures using electrocautery — urgent
Symptoms: Not a patient-recognised symptom; this is a procedural safety issue.
Action: Tell your medical team you take lactulose before any colonoscopy, proctoscopy, or similar procedure using electrocautery, so appropriate bowel preparation with a non-fermentable solution can be used first. (1)
Liver function changes —
Action: Seek immediate medical attention if signs of allergic reaction or liver problems occur. Contact your healthcare provider before stopping treatment.
Interactions
| Medicine or test | Effect | Action |
|---|---|---|
| Neomycin and other anti-infective medicines | May reduce lactulose's effectiveness by eliminating the colonic bacteria lactulose relies on. | Tell your prescriber about all antibiotics you take. (1) |
| Nonabsorbable antacids | May reduce lactulose's desired acidifying effect in the colon. | Tell your prescriber or pharmacist about antacid use. (1) |
| Other laxatives | Combined use, especially when starting lactulose, can make bowel effects harder to predict. | Avoid combining with other laxatives unless your prescriber advises it. (1) |
Pregnancy, breastfeeding, kidney/liver function, age
Diabetes
Lactulose contains galactose and lactose; use with caution and discuss with your prescriber. (1)
Pregnancy and breastfeeding
Animal studies have not shown fetal harm, but human data are limited; use only if your prescriber judges it clearly needed. It is not known whether lactulose passes into breast milk in a way that affects a nursing infant, so use with caution. (1)
Children
Age-specific doses apply for children; use in children under 14 requires a doctor's guidance. (2)
Infants
Infants are at particular risk of low sodium levels and dehydration with lactulose use; this should be closely supervised by a clinician. (1)
Monitoring
Before starting
- Confirm whether the goal is constipation relief or hepatic-encephalopathy management, since dosing differs substantially.
- Screen for galactosemia/low-galactose-diet requirement and diabetes.
During treatment
- Watch for excessive diarrhoea, dehydration, or electrolyte disturbance, especially at high hepatic-encephalopathy doses.
- For hepatic encephalopathy, response is often judged by mental state and stool frequency, per the treating clinician's plan.
Storage
Store as directed on the product label, out of reach of children.
Professional information
Clinician-facing context only. Use the current local product information for exact dosing.
United Kingdom
Indication: Constipation
Dose summary: Adults: 15 mL twice daily as a starting dose, adjusted by response. Children 5-17: 5-20 mL twice daily. Children 1-4: 2.5-10 mL twice daily. Infants 1-11 months: 2.5 mL twice daily. Use in children under 14 requires doctor approval. Typical duration up to about a week unless the prescriber advises otherwise.
Renal context: Not established in the sources reviewed for this dossier. (2)
United States / United Kingdom
Indication: Hepatic encephalopathy
Dose summary: US label: starting dose 30 mL 3 times daily; hourly 30-45 mL doses may be used initially to induce rapid laxation, then reduced to a maintenance dose. UK guidance: adult dose 30-50 mL three times daily. Treatment may continue for many months for this indication.
Renal context: Not established in the sources reviewed for this dossier. (1) (2)
Hepatic guidance
Recognise that serious underlying liver disease may require additional therapy beyond lactulose alone.
Overdose note
Excessive dosing can cause diarrhoea, dehydration, hypokalemia, and hypernatremia; manage supportively per local guidance. (1)
Frequently asked questions
What is lactulose used for?
lactulose is prescribed for approved indications. Always follow your healthcare provider's guidance.
What are the side effects of lactulose?
Common side effects may include gastrointestinal symptoms and headache. Serious side effects require immediate medical attention.
Can I take lactulose with other medications?
Always inform your healthcare provider about all medications you are taking, including over-the-counter products and supplements.
What is the mechanism of action of lactulose?
Lactulose passes largely unchanged to the colon, where bacterial metabolism produces low-molecular-weight organic acids that acidify colonic contents; this osmotic effect draws water into the bowel and, in hepatic encephalopathy, reduces blood ammonia by an estimated 25-50%, correlating with improvement in mental state and EEG patterns. (1)
References
- LACTULOSE SOLUTION - lactulose solution USP, 10 g/15 mL — prescribing informationDailyMed, U.S. National Library of Medicine (FDA-approved label) · United States · accessed 2026-07-26 · source 1
- LactuloseNHS (United Kingdom) · United Kingdom · accessed 2026-07-26 · source 2
- LACTULOSE SOLUTION [APOZEAL PHARMACEUTICALS INC] — US prescribing information (DailyMed SPL)U.S. National Library of Medicine (DailyMed) · US · accessed 2026-08-14 · source 3
- Lactulose — patient drug information (MedlinePlus)U.S. National Library of Medicine (MedlinePlus) · US · accessed 2026-08-14 · source 4
- Enulose — FDA approval record (Drugs@FDA ANDA090502)U.S. Food and Drug Administration · US · accessed 2026-08-14 · source 5
- lactulose — RxNorm normalized drug concept (RXCUI 6218)U.S. National Library of Medicine (RxNorm) · US · accessed 2026-08-14 · source 6
Brand names by country
Single-ingredient lactulose names are shown separately by country. Product availability, strengths, and supply rules can change; combination products are not included here.
Priority countries
United States
- Enulose10 g5mL · actavis pharma, inc.
- KRISTALOSE20 g/20g, 10 g0g · cumberland pharmaceuticals inc.
- LACTULOSE Crystalline20 g/20g, 10 g0g · cumberland assured products inc.
- Generlac10 g5mL · chartwell rx, llc
- Constulose10 g5mL · actavis pharma, inc.
Canada
- PHARMA-LACTULOSE
- PMS-LACTULOSE SYR