NutriDex

The Supplement Research Compendium
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Lactulose

Galactose-fructose disaccharide

Synthetic galactose-fructose disaccharide: osmotic laxative, ammonia-lowering therapy, and bifidogenic prebiotic

Strong evidence 🌾Prebiotics & Fibers🛡️Gut & Immune

✚ Updated · How we grade evidence

Evidence tier
Strong
Research weight
Citations
9 verified / 9
Classification
Prebiotics & Fibers
❝
What the evidence says. Multiple high-quality RCTs / meta-analyses with consistent effects.

What is Lactulose?

Lactulose (Galactose-fructose disaccharide) is a prebiotic fiber used for reduces mortality and improves/prevents overt hepatic encephalopathy in cirrhosis (cochrane rr ~0.59 for death; ~0.58 for he) by trapping gut-derived ammonia as ammonium and accelerating its excretion. NutriDex grades the human evidence as Strong. Lactulose is a non-absorbable synthetic disaccharide (galactose linked to fructose) that passes undigested to the colon, where bacteria ferment it into short-chain fatty acids that acidify the lumen, trap ammonia as ammonium, and exert an osmotic laxative effect. Its strongest evidence is in hepatic encephalopathy: a 2016 Cochrane review of randomized trials found non-absorbable disaccharides reduce mortality (RR ~0.59) and improve/prevent overt and minimal encephalopathy, making it first-line therapy. For chronic constipation it reliably increases stool frequency, though head-to-head trials show polyethylene glycol (PEG/macrogol) outperforms it on most outcomes. At low (sub-laxative) doses lactulose acts as a bifidogenic prebiotic and modestly enhances colonic calcium absorption, but these microbiome and mineral-absorption uses rest on smaller, shorter trials and are less robust than its gastroenterology indications.

Purported Benefits

✓Reduces mortality and improves/prevents overt hepatic encephalopathy in cirrhosis (Cochrane RR ~0.59 for death; ~0.58 for HE) by trapping gut-derived ammonia as ammonium and accelerating its excretion
✓Reverses minimal hepatic encephalopathy and improves cognition and quality of life (multicenter RCT: 64% vs 23% reversal at 60 days)
✓Increases stool frequency and softens stool in chronic constipation (network meta-analysis: ~+3.4 weekly bowel movements vs placebo), an osmotic/fermentative laxative effect
✓Bifidogenic prebiotic at low doses: selectively increases Bifidobacterium and Lactobacillus and boosts colonic short-chain fatty acid (SCFA) production while lowering luminal pH
✓Modestly enhances colonic calcium absorption in a dose-dependent manner (postmenopausal crossover trial: ~28% to ~32% fractional absorption), with similar signals for magnesium
✓First-line agent for primary and secondary prophylaxis of recurrent encephalopathy, reducing serious cirrhosis complications (liver failure, bleeding, infection)

Evidence by outcome

The same supplement can be well-proven for one use and unproven for another — here is the human evidence graded outcome by outcome.

OutcomeEvidenceEffectStudies
Reduces mortality in hepatic encephalopathyCochrane (24 RCTs): non-absorbable disaccharides reduce death (RR 0.59). First-line, robust. Strong ↑ benefit · large 1
Improves/reverses overt and minimal hepatic encephalopathyCochrane, meta-analysis, and multicenter RCT (64% vs 23% MHE reversal) all consistent. Strong ↑ benefit · large 3
Increases stool frequency in chronic constipationNetwork meta-analysis: +3.4 weekly BMs vs placebo; but PEG outperforms it head-to-head. Strong ↑ benefit · moderate 2
Bifidogenic prebiotic effect (microbiome/SCFA)Low-dose bifidogenic/SCFA effect rests on smaller, shorter trials and review-level data. Preliminary ↑ benefit · moderate 1
Enhances colonic calcium absorptionSingle small crossover trial (n=12) showed dose-dependent rise (27.7%→32.2%); limited evidence. Preliminary ↑ benefit · small 1

Dosing & Compounds

Typical Dose
Constipation: 15-30 mL syrup (10-20 g) once daily, titrated to 2-3 soft stools/day. Overt hepatic encephalopathy: 30-45 mL (20-30 g) every 1-2 hours until catharsis, then 30-45 mL 2-4x daily targeting 2-3 soft stools/day; can be given by enema (300 mL in 700 mL water) if obtunded. Minimal HE: ~30-60 mL/day in divided doses. Prebiotic/mineral-absorption use: lower 3-10 g/day. Taken orally, may be mixed with water, juice or food to improve palatability.
Active Compounds
Prescription/OTC oral solutions: Duphalac, Cephulac, Kristalose (crystalline powder), Constulose, Enulose, Generlac, LactugalGeneric lactulose syrup (typically 10 g per 15 mL); rectal enema formulations for acute encephalopathyFunctional-food / prebiotic ingredient in some yogurts and infant/medical nutrition (mainly Japan/Europe)Not a natural food fiber - lactulose is synthesized industrially from lactose (trace amounts form in heated/UHT milk)

Safety & Cautions

Highly fermentable (high-FODMAP), so flatulence, bloating, abdominal cramping and an initially sweet taste are common, especially when starting or at laxative doses; nausea and diarrhea signal overdosing. Overuse can cause excess watery diarrhea with dehydration and electrolyte disturbance (hypokalemia, hypernatremia), particularly in the elderly and in encephalopathy where over-titration may itself precipitate confusion. Contraindicated in galactosemia (contains galactose) and in suspected bowel obstruction; use caution in diabetes (contains some free galactose/lactose). Like other fibers/osmotics it can alter absorption of co-ingested drugs; avoid combining with other laxatives when titrating in encephalopathy. Generally considered safe in pregnancy and as a constipation treatment in children. Unlike glucomannan/konjac it poses no choking/esophageal-obstruction risk. Educational only — always check with your doctor or pharmacist before combining Lactulose with any medicine.

Key Studies

Network meta-analysis Mehta 2024 ✓ PubMed
Network meta-analysis of 37 RCTs (3903 adults): lactulose increased weekly stool movements vs placebo (mean difference 3.39, 95% CI 1.13-5.65; moderate certainty).
Meta-analysis Bhatti Cureus 2024 ✓ Full text
Systematic review and network meta-analysis (43 studies, 19,622 patients) ranked combined lactulose plus rifaximin most effective for preventing overt HE vs placebo (RR 0.19, 95% CI 0.09-0.40) and superior to lactulose alone (RR 0.57, 95% CI 0.36-0.92).
Meta-analysis Frontiers in Medicine 2025 ✓ Full text
Meta-analysis of 12 RCTs (858 patients) found L-ornithine L-aspartate plus lactulose was 31% more effective than lactulose alone for hepatic encephalopathy (RR 1.31, 95% CI 1.22-1.42) and lowered blood ammonia (MD -13.02, 95% CI -15.69 to -10.36) without increasing adverse events.
Cochrane systematic review Gluud 2016 (Cochrane) ✓ PubMed
In 24 RCTs (n=1487) non-absorbable disaccharides reduced mortality vs placebo/no intervention (RR 0.59, 95% CI 0.40-0.87) and improved hepatic encephalopathy (RR 0.58, 95% CI 0.50-0.69; 22 RCTs).
Meta-analysis Luo 2011 ✓ PubMed
Meta-analysis of 9 RCTs (434 patients) found lactulose significantly improved neuropsychological test performance in minimal hepatic encephalopathy (RR for no improvement 0.52, 95% CI 0.44-0.62).
Cochrane systematic review Lee-Robichaud 2010 (Cochrane) ✓ PubMed
Cochrane review (10 RCTs) found polyethylene glycol superior to lactulose for stool frequency, stool form and need for additional laxatives in chronic constipation.
Randomized controlled trial Wang 2019 ✓ PubMed
Multicenter RCT in minimal HE: day-60 MHE reversal rate 64.2% with lactulose vs 22.6% control (P=.0002), with improved cognition, quality of life and gut microbiota.
Randomized crossover trial van den Heuvel 1999 ✓ Source
Randomized double-blind crossover in 12 postmenopausal women: fractional calcium absorption rose dose-dependently with lactulose (27.7% reference vs 32.2% at 10 g/day; P<0.01).
Narrative review Karakan 2021 ✓ Full text
Review of human and mechanistic data showing low-dose (sub-laxative) lactulose acts as a bifidogenic prebiotic, increasing Bifidobacterium/SCFA and enhancing mineral absorption.
9 sources cited · 9 verified Search all studies on PubMed ↗

Common questions about Lactulose

What is Lactulose used for?

Lactulose is most often taken for Reduces mortality and improves/prevents overt hepatic encephalopathy in cirrhosis (Cochrane RR ~0.59 for death; ~0.58 for HE) by trapping gut-derived ammonia as ammonium and accelerating its excretion, Reverses minimal hepatic encephalopathy and improves cognition and quality of life (multicenter RCT: 64% vs 23% reversal at 60 days), Increases stool frequency and softens stool in chronic constipation (network meta-analysis: ~+3.4 weekly bowel movements vs placebo), an osmotic/fermentative laxative effect, Bifidogenic prebiotic at low doses: selectively increases Bifidobacterium and Lactobacillus and boosts colonic short-chain fatty acid (SCFA) production while lowering luminal pH. Synthetic galactose-fructose disaccharide: osmotic laxative, ammonia-lowering therapy, and bifidogenic prebiotic

Does Lactulose work — what does the evidence say?

Strong evidence. Multiple high-quality RCTs / meta-analyses with consistent effects. Lactulose is a non-absorbable synthetic disaccharide (galactose linked to fructose) that passes undigested to the colon, where bacteria ferment it into short-chain fatty acids that acidify the lumen, trap ammonia as ammonium, and exert an osmotic laxative effect. Its strongest evidence is in hepatic encephalopathy: a 2016 Cochrane review of randomized trials found non-absorbable disaccharides reduce mortality (RR ~0.59) and improve/prevent overt and minimal encephalopathy, making it first-line therapy. For chronic constipation it reliably increases stool frequency, though head-to-head trials show polyethylene glycol (PEG/macrogol) outperforms it on most outcomes. At low (sub-laxative) doses lactulose acts as a bifidogenic prebiotic and modestly enhances colonic calcium absorption, but these microbiome and mineral-absorption uses rest on smaller, shorter trials and are less robust than its gastroenterology indications.

What is the typical dose of Lactulose?

Constipation: 15-30 mL syrup (10-20 g) once daily, titrated to 2-3 soft stools/day. Overt hepatic encephalopathy: 30-45 mL (20-30 g) every 1-2 hours until catharsis, then 30-45 mL 2-4x daily targeting 2-3 soft stools/day; can be given by enema (300 mL in 700 mL water) if obtunded. Minimal HE: ~30-60 mL/day in divided doses. Prebiotic/mineral-absorption use: lower 3-10 g/day. Taken orally, may be mixed with water, juice or food to improve palatability.

Is Lactulose safe? Any cautions or side effects?

Highly fermentable (high-FODMAP), so flatulence, bloating, abdominal cramping and an initially sweet taste are common, especially when starting or at laxative doses; nausea and diarrhea signal overdosing. Overuse can cause excess watery diarrhea with dehydration and electrolyte disturbance (hypokalemia, hypernatremia), particularly in the elderly and in encephalopathy where over-titration may itself precipitate confusion. Contraindicated in galactosemia (contains galactose) and in suspected bowel obstruction; use caution in diabetes (contains some free galactose/lactose). Like other fibers/osmotics it can alter absorption of co-ingested drugs; avoid combining with other laxatives when titrating in encephalopathy. Generally considered safe in pregnancy and as a constipation treatment in children. Unlike glucomannan/konjac it poses no choking/esophageal-obstruction risk.

How many studies support Lactulose?

NutriDex cites 9 sources for Lactulose, graded "Strong".

Cite this page
APA

Peh, D. (2026). Lactulose (Galactose-fructose disaccharide): Benefits, Dosage, Side Effects & Evidence. NutriDex — The Supplement Research Compendium. Retrieved 26 Jun 2026, from https://nutridex.info/s/lactulose

BibTeX
@misc{nutridex_lactulose,
  author       = {Peh, Daryl},
  title        = {Lactulose (Galactose-fructose disaccharide): Benefits, Dosage, Side Effects \& Evidence},
  year         = {2026},
  howpublished = {NutriDex --- The Supplement Research Compendium},
  url          = {https://nutridex.info/s/lactulose},
  note         = {Reviewed by Dr Daryl Peh, MBBS Singapore, MMed FM. Accessed 2026-06-26}
}

For medical claims, citing the underlying primary studies linked above is preferred. NutriDex is an educational reference, not medical advice.

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