Lactulose
Lactulose is a non-absorbable disaccharide that works as an osmotic laxative, drawing water into the colon to soften stool and stimulate bowel movements. It is primarily used to treat chronic constipation and reduce blood ammonia levels in patients with liver disease. This medication is suitable for adults and children and is often preferred for its gentle action and lack of dependency risk.
Lactulose is an osmotic laxative used to treat constipation and reduce ammonia levels in liver disease by drawing water into the colon.
Key facts at a glance
- ATC
- A06AD11
- Generic
- Lactulose
- Class
- laxative
- Brands
- Constulose
- Availability
- behind_counter
- Pregnancy
- B
- Lactation
- safe
- Onset (min)
- 720
- Routes
- oral
- Forms
- oral-solution
- Regions
- CN, US, EU, JP
- Monitoring
- —
This page is for informational purposes only.
Do not use this information to diagnose yourself or to replace a physician's advice. Always consult a qualified healthcare provider before starting, stopping, or changing any medication. If you believe you are experiencing a medical emergency, call your local emergency number immediately.
Dosage and administration
- Usual dose
- 500mg twice daily
- Maximum
- consult physician
- Frequency
- every 12 hours
- Instructions
- Follow physician instructions
- Duration limits
- as prescribed
- Monitoring
- standard
- Usual dose
- 250mg twice daily
- Maximum
- consult physician
- Frequency
- every 12 hours
- Instructions
- Follow physician instructions
- Duration limits
- as prescribed
- Monitoring
- standard
- Usual dose
- 400mg daily
- Maximum
- consult physician
- Frequency
- once daily
- Instructions
- Follow physician instructions
- Duration limits
- as prescribed
- Monitoring
- standard
Overdose information
Special Populations
7 groupspregnancy
generaluse lowest effective dose
use only if clearly needed and benefits outweigh potential risks
monitor for electrolyte balance
Use with caution and monitor for adverse effects.
lactation
generalno adjustment needed
generally considered safe for use during breastfeeding
none required
geriatric
over 65 yearsstart with lower doses and titrate slowly
use with caution due to increased risk of electrolyte imbalance and dehydration
monitor electrolytes and hydration status regularly
Use with caution and monitor for adverse effects.
pediatric_age
children 2 12 yearsweight-based dosing recommended
use under medical supervision in children; dose according to age and weight
monitor for adequate hydration and electrolyte balance
renal_impairment
mild to moderateno dose adjustment typically required but monitor closely
use with caution; monitor electrolytes due to potential for potassium loss
regular monitoring of electrolytes especially potassium
Use with caution and monitor for adverse effects.
hepatic_impairment
cirrhosis with encephalopathydosing individualized based on response
commonly used for hepatic encephalopathy; dose titrated to produce 2-3 soft stools daily
monitor mental status and electrolytes frequently
Use with caution and monitor for adverse effects.
alcohol_users
chronic alcohol useuse with caution
ensure adequate hydration; monitor for electrolyte imbalances common in alcohol users
monitor electrolytes and renal function
Use with caution and monitor for adverse effects.
Statistics and clinical data
Drug class
Lactulose is classified as an osmotic laxative (ATC code A06AD07)
Primary indications
Main therapeutic uses of lactulose in clinical practice
Mechanism of action
Lactulose draws water into the colon to soften stools
FDA approval year
Year lactulose was approved for medical use in the United States
Treatment of chronic constipation, hepatic encephalopathy (to reduce blood ammonia levels and prevent recurrence), and relief of portal-systemic encephalopathy. Also used to soften stool in patients with hemorrhoids or after anorectal surgery.
Lactulose is a synthetic disaccharide that is not absorbed in the small intestine. It reaches the colon intact where bacteria metabolize it into lactic acid and acetic acid. This acidifies the colonic contents, drawing water osmotically into the lumen to soften stool and promote peristalsis. For liver disease, acidification converts ammonia (NH3) to ammonium (NH4+), which cannot be absorbed, reducing blood ammonia levels.
May take 24-48 hours to produce a bowel movement. Common side effects include abdominal cramping, flatulence, and diarrhea (if dosed too high). Should be used with caution in patients with diabetes (contains galactose and lactose) and those requiring a low-galactose diet. Electrolyte imbalance may occur with prolonged use or overdose.
Contraindications
Conditions and patient states where this medication should be avoided or used with caution.
Do not use (1)
Known allergy to this medication or its components
Use caution (1)
Consult healthcare provider for benefits vs risks assessment
Official drug label
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This information is for educational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment.
This content is for general informational and educational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment. Always seek the guidance of a qualified healthcare provider with any questions you have about a medical condition, and never disregard professional medical advice or delay seeking it because of something you read here.
If you think you may have a medical emergency, call your local emergency number or go to the nearest emergency department immediately.
Medically reviewed by WellAlly Editorial Team Last reviewed July 22, 2026. · Read our editorial policy