Lactulose
Galactose-fructose disaccharide
Synthetic galactose-fructose disaccharide: osmotic laxative, ammonia-lowering therapy, and bifidogenic prebiotic
Evidence tier
Strong
Research weight
Citations
12 verified / 12
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.
| Outcome | Evidence | Effect | Studies |
|---|---|---|---|
| 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
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 ★ 12 studies
Meta-analysis
Lou 2026
✓ PubMed
Systematic review and meta-analysis of small intestinal bacterial overgrowth prevalence in functional gastrointestinal disorders.
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).
Review
Pyrsopoulos 2026
✓ PubMed
Narrative review on reducing the risk of overt hepatic-encephalopathy recurrence, where lactulose is first-line therapy.
Review
Sacco 2026
✓ PubMed
Quality of Life in Patients with Hepatic Encephalopathy Treated with Rifaximin: A Systematic Review
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.