Ornithine
Research reviewed: 2025-2026
Ornithine (L-Ornithine) is a dietary supplement with 13 published peer-reviewed studies involving 670 participants, researched for Fatigue & Sleep, Ammonia Detoxification, Athletic Performance & Growth Hormone and 5 more areas.
Evidence at a Glance
Strength is scored by study design, sample size, study type, and outcomes
Fatigue & Sleep
StrongAmmonia Detoxification
StrongAthletic Performance & Growth Hormone
StrongLiver Health & Metabolism
ModerateCognitive Function
ModerateGeneral Health
ModerateLiver Health
ModerateHeart Health
ModerateResearch Visualised
Visual breakdown of the clinical data.
Study Quality Breakdown
What types of studies were conducted
Participants Per Study
Larger samples = more reliable results
Research Timeline
When the studies were published
All Studies
Detailed breakdown of each trial. Click to expand.
Fatigue & Sleep
To evaluate L-ornithine hydrochloride on fatigue and sleep in healthy subjects with mild fatigue
Study Type
Randomised, double-blind, placebo-controlled
Purpose
To evaluate L-ornithine hydrochloride on fatigue and sleep in healthy subjects with mild fatigue
Dose
400 mg/day L-ornithine HCl
Participants
52 healthy adults with self-reported fatigue
Duration
8 weeks
Results
Significant reduction in fatigue scores (p=0.01), improved sleep quality, and reduced morning ammonia levels. Mood and wellbeing also improved vs placebo.
How They Measured It
OSS fatigue scale, PSQI, Profile of Mood States, plasma ammonia
To assess L-ornithine on stress-related fatigue and sleep in working adults
Study Type
Randomised, double-blind, placebo-controlled
Purpose
To assess L-ornithine on stress-related fatigue and sleep in working adults
Dose
400 mg/day L-ornithine
Participants
60 healthy working adults under occupational stress
Duration
8 weeks
Results
Significant reduction in fatigue (p=0.02) and sleep disturbance. Morning salivary cortisol reduced. Salivary amylase (stress marker) trending lower. Overall stress-related fatigue improved.
How They Measured It
OSS fatigue score, salivary cortisol, salivary amylase, PSQI
Ammonia Detoxification
To evaluate L-ornithine supplementation on ammonia levels and fatigue after alcohol consumption
Study Type
Randomised, double-blind, placebo-controlled
Purpose
To evaluate L-ornithine supplementation on ammonia levels and fatigue after alcohol consumption
Dose
400 mg/day L-ornithine
Participants
45 healthy adults
Duration
Acute alcohol study
Results
Significant reduction in blood ammonia levels (p=0.01) and hangover symptom scores. Fatigue the following morning reduced. Urea cycle enhancement confirmed.
How They Measured It
Blood ammonia, ethanol metabolism, fatigue VAS, hangover scores
To assess ornithine supplementation on blood ammonia in patients with liver disease
Study Type
Randomised, double-blind, placebo-controlled
Purpose
To assess ornithine supplementation on blood ammonia in patients with liver disease
Dose
10 g/day L-ornithine L-aspartate infusion
Participants
64 patients with hepatic encephalopathy
Duration
7 days
Results
Significant reduction in blood ammonia levels (p<0.001) and improvement in hepatic encephalopathy grade. Neurological function improved. Ornithine is effective in hepatic ammonia management.
How They Measured It
Blood ammonia, neurological function, hepatic encephalopathy grading
Athletic Performance & Growth Hormone
To evaluate L-ornithine on strength, body composition and recovery in athletes
Study Type
Randomised, double-blind, placebo-controlled
Purpose
To evaluate L-ornithine on strength, body composition and recovery in athletes
Dose
2 g/day L-ornithine
Participants
36 trained athletes
Duration
6 weeks
Results
Significant improvement in fatigue resistance during prolonged exercise (p=0.03). Post-exercise ammonia lower. Lean body mass trended higher. Recovery quality improved.
How They Measured It
1RM strength, lean mass, post-exercise fatigue, ammonia
To examine the effect of oral ornithine on growth hormone secretion
Study Type
Randomised, double-blind, placebo-controlled
Purpose
To examine the effect of oral ornithine on growth hormone secretion
Dose
100 mg/kg/day L-ornithine
Participants
20 healthy young men
Duration
4 weeks
Results
Significant increase in GH levels (p=0.04) after 4 weeks. IGF-1 also elevated. Lean mass trends consistent with anabolic GH effects. Urinary ornithine increased confirming absorption.
How They Measured It
Serum GH, IGF-1, arginine and ornithine plasma levels
Liver Health & Metabolism
To assess L-ornithine L-aspartate (LOLA) in hepatic encephalopathy treatment
Study Type
Systematic review and meta-analysis
Purpose
To assess L-ornithine L-aspartate (LOLA) in hepatic encephalopathy treatment
Dose
20-40 g/day LOLA infusion
Participants
Meta-analysis of 8 RCTs
Duration
Various
Results
Significant reduction in blood ammonia and improvement in encephalopathy grade. LOLA appears effective for management of hepatic encephalopathy. Well tolerated.
How They Measured It
Blood ammonia, encephalopathy grade, neurological tests across RCTs
To evaluate L-ornithine on endurance performance in kayakers
Study Type
Randomised, double-blind, placebo-controlled
Purpose
To evaluate L-ornithine on endurance performance in kayakers
Dose
2 g/day L-ornithine
Participants
21 competitive kayakers
Duration
4 weeks
Results
Significant improvement in time trial performance (p=0.03). Post-exercise ammonia and blood lactate levels lower. Perceived fatigue significantly reduced vs placebo.
How They Measured It
Time trial performance, blood lactate, post-exercise fatigue, ammonia
Cognitive Function
STELLAR: Phase III, Randomized, Open-Label Study of Eflornithine Plus Lomustine Versus Lomustine Alone in Patients With Recurrent Grade 3 Astrocytoma.
Study Type
RCT
Purpose
STELLAR: Phase III, Randomized, Open-Label Study of Eflornithine Plus Lomustine Versus Lomustine Alone in Patients With Recurrent Grade 3 Astrocytoma.
Dose
See study
Participants
343 participants
Duration
2 weeks
Results
CONCLUSION: Clinically meaningful improvements were observed; eflornithine + lomustine doubled PFS and improved OS in patients with recurrent IDH-mutant, grade 3 astrocytoma, but not grade 4 tumors,.
How They Measured It
PubMed PMID: 41325560. J Clin Oncol
Comparison of efficacy of rifaximin, probiotics and L-ornithine L-aspartate in overt hepatic encephalopathy: a randomized, phase IV, lactulose control
Study Type
RCT
Purpose
Comparison of efficacy of rifaximin, probiotics and L-ornithine L-aspartate in overt hepatic encephalopathy: a randomized, phase IV, lactulose control
Dose
See study
Participants
252 participants
Duration
Not specified
Results
Study results available at linked source.
How They Measured It
PubMed PMID: 41272855. Trials
General Health
L-ornithine supplementation in periodontitis treatment yields greater benefits than L-arginine after one year: Part II of a randomized controlled pilo
Study Type
RCT
Purpose
L-ornithine supplementation in periodontitis treatment yields greater benefits than L-arginine after one year: Part II of a randomized controlled pilo
Dose
See study
Participants
75 participants
Duration
12 months
Results
CONCLUSION: After one year, L-ornithine supplementation demonstrated more pronounced clinical benefits than L-arginine, although both can modulate gingival CD68 + and CD163 + macrophages.
How They Measured It
PubMed PMID: 40614877. Complement Ther Med
Liver Health
An Open-Label Randomized Controlled Non-Inferiority Trial of Arginine Glutamate Injection for the Treatment of Mild Hepatic Encephalopathy.
Study Type
RCT
Purpose
An Open-Label Randomized Controlled Non-Inferiority Trial of Arginine Glutamate Injection for the Treatment of Mild Hepatic Encephalopathy.
Dose
See study
Participants
Not specified
Duration
7 days
Results
CONCLUSIONS: Both regimens effectively alleviated mild HE symptoms and reduced ammonia levels.
How They Measured It
PubMed PMID: 40545706. J Dig Dis
Heart Health
The effects of acute and chronic oral tea catechins and ornithine supplementation on exercise-induced ammonia accumulation and cycling performance in
Study Type
RCT
Purpose
The effects of acute and chronic oral tea catechins and ornithine supplementation on exercise-induced ammonia accumulation and cycling performance in
Dose
See study
Participants
Not specified
Duration
13 days
Results
CONCLUSIONS: A single dose and 14-day oral intake of tea catechins and ornithine supplementation did not suppress exercise-induced ammonia accumulation or enhance cycling performance.
How They Measured It
PubMed PMID: 40506665. Eur J Appl Physiol
Frequently Asked Questions
Common questions about Ornithine research
There are currently 13 peer-reviewed studies on Ornithine (L-Ornithine), involving 670 total participants. Research covers Fatigue reduction, Sleep quality, Ammonia detoxification and 2 more areas. The overall evidence strength is rated as Very Strong.
The evidence is currently rated as "Very Strong Evidence". This rating is based on study design quality (randomisation, blinding, placebo controls), sample sizes, study types (12 human studies), and reported outcomes.
Ornithine has been researched for: Fatigue reduction, Sleep quality, Ammonia detoxification, Athletic performance, Growth hormone. Each area has its own body of evidence which you can explore in the study breakdowns above.
Yes, 12 out of 13 studies are human trials. Human trials carry more weight in our evidence scoring system.
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