L-Ornithine
Also known as: ornithine, L-ornithine (amino acid), ornithine alpha-ketoglutarate (OKG)
A 7‑day cross‑over RCT found 400 mg oral L‑ornithine delayed dim light melatonin onset by about 15 minutes in healthy adults. Enteral ornithine alpha‑ketoglutarate (OKG) in burn patients was associated with increased production of proline, glutamine and arginine and, in one randomized trial, shorter wound healing time versus an isonitrogenous control. A small 8‑week pilot trial of a collagen+ornithine drink reported improved skin elasticity and transepidermal water loss with increased plasma IGF‑1, but the effect cannot be attributed to ornithine alone because the product was a composite.
Last reviewed: 2026-10-14 · 4 indexed studies
Set your location for accurate regulatory status
Saved on this device — no sign-in needed.
Overview
L‑ornithine is a non-proteinogenic amino acid involved in the urea cycle and nitrogen metabolism. Human trials reported modest effects on circadian phase with oral L‑ornithine and benefits on wound healing or skin parameters in studies using ornithine-containing enteral or combined supplements.
Mechanism & Function
Mechanism of Action
Ornithine is a urea cycle intermediate and is metabolised to proline, glutamine and arginine (evidenced in OKG studies). These metabolites may affect tissue repair and anabolic signalling; in one human trial L‑ornithine ingestion shifted a marker of central circadian phase (melatonin onset), suggesting central clock modulation by diet-derived amino acids.
Physiological Role
Urea cycle intermediate; precursor for proline, polyamines and arginine; participates in nitrogen disposal and intermediary metabolism.
Primary Pathways
Performance / Health Relevance
Ornithine (and OKG) have been studied for clinical recovery and tissue repair in burns and for potential modulation of sleep/circadian timing; evidence for direct ergogenic performance benefits in healthy athletic populations is limited in the provided trials.
Evidence Review
No meta-analyses or systematic reviews indexed for this ingredient yet.
Dimensions marked N/A have no indexed evidence of that class. They are shown as unavailable rather than scored.
Practical Use & Dosage
- Minimum Effective Dose
- 400 mg (single study showing a 15‑minute delay in dim light melatonin onset after 7 days of 400 mg/day)
- Optimal Range
- Not established; clinical enteral OKG studies used bolus 10 g or continuous 10–30 g/day, while a composite product with ornithine was used daily (dose of ornithine within product not specified in abstract).
- Upper / Caution Level
- Not established (OKG enteral dosing up to 30 g/day reported in burn patients; safety was reported as acceptable in that trial).
- Timing
- In the circadian RCT 400 mg was taken daily for 7 days; OKG was given as bolus doses twice daily or as continuous infusion in clinical studies.
- Best Format
- Oral capsule, drink or enteral formulation (OKG) depending on context.
- Bioavailability
- OKG is extensively metabolised after enteral administration, producing proline, glutamine and arginine; pharmacokinetics followed first‑order kinetics in burn patients.
- Absorption Considerations
- Modes of administration (bolus vs continuous enteral infusion) affect metabolite production; bolus dosing appeared to yield higher glutamine and arginine production in the cited study.
Safety & Interactions
Side Effects
- •No major adverse effects reported in the cited trials; OKG was reported as safe and well tolerated in a burn patient trial
Contraindications
- Disorders of the urea cycle or other inborn errors of amino acid metabolism — clinical context may alter appropriateness
Drug Interactions
- •Not reported in provided abstracts
Who Should Avoid
- •Individuals with known urea cycle disorders or metabolic conditions without medical supervision
Monitoring
In clinical settings monitoring of nitrogen balance and relevant metabolite levels (arginine, glutamine, proline) was performed in trials; routine monitoring not specified for healthy use.
Frequently Asked Questions
Auto-generated from indexed evidence — dosage, safety, interactions, and more.
When is L-Ornithine typically used or indicated?
L-Ornithine is most commonly used for: Support for sleep/circadian regulation, Support for wound healing and recovery (enteral OKG in clinical settings), Cosmetic/skin condition supplements (combined formulations). Urea cycle intermediate; precursor for proline, polyamines and arginine; participates in nitrogen disposal and intermediary metabolism.
How does L-Ornithine work?
Ornithine is a urea cycle intermediate and is metabolised to proline, glutamine and arginine (evidenced in OKG studies). These metabolites may affect tissue repair and anabolic signalling; in one human trial L‑ornithine ingestion shifted a marker of central circadian phase (melatonin onset), suggesting central clock modulation by diet-derived amino acids.
What is the recommended dose of L-Ornithine?
The optimal range is Not established; clinical enteral OKG studies used bolus 10 g or continuous 10–30 g/day, while a composite product with ornithine was used daily (dose of ornithine within product not specified in abstract).. with a minimum effective dose of 400 mg (single study showing a 15‑minute delay in dim light melatonin onset after 7 days of 400 mg/day). Best taken: In the circadian RCT 400 mg was taken daily for 7 days; OKG was given as bolus doses twice daily or as continuous infusion in clinical studies.. Upper / caution level: Not established (OKG enteral dosing up to 30 g/day reported in burn patients; safety was reported as acceptable in that trial)..
What are the side effects of L-Ornithine?
Reported side effects include: No major adverse effects reported in the cited trials; OKG was reported as safe and well tolerated in a burn patient trial. Monitoring: In clinical settings monitoring of nitrogen balance and relevant metabolite levels (arginine, glutamine, proline) was performed in trials; routine monitoring not specified for healthy use.
Does L-Ornithine interact with medications?
Known or theoretical interactions: Not reported in provided abstracts. Always check with a clinician before combining with prescription medication.
Who should avoid L-Ornithine?
L-Ornithine is generally not recommended for: Individuals with known urea cycle disorders or metabolic conditions without medical supervision; and Disorders of the urea cycle or other inborn errors of amino acid metabolism — clinical context may alter appropriateness.
How strong is the evidence for L-Ornithine?
Evidence level: Moderate (overall score 70/100), based on 4 indexed studies on SuppIndex.
Research & References (4)
A randomized, double-blind and placebo-controlled crossover trial on the effect of l-ornithine ingestion on the human circadian clock.
Randomized, double‑blind placebo‑controlled crossover trial in 28 healthy adults testing oral L‑ornithine 400 mg daily for 7 days versus placebo; saliva melatonin profiles measured under dim light.
Ornithine alpha-ketoglutarate metabolism after enteral administration in burn patients: bolus compared with continuous infusion.
Kinetic study in 42 burn patients receiving enteral ornithine alpha‑ketoglutarate (OKG) as bolus (10 g) or continuous infusion (10, 20, 30 g/day) or isonitrogenous control; plasma ornithine and metabolite production measured.
Ornithine alpha-ketoglutarate improves wound healing in severe burn patients: a prospective randomized double-blind trial versus isonitrogenous controls.
Prospective randomized double‑blind trial in 47 severe burn patients comparing enteral ornithine alpha‑ketoglutarate (2×10 g/day) with an isonitrogenous control for 3 weeks; wound healing time and markers of protein catabolism assessed.
Effects of Composite Supplement Containing Collagen Peptide and Ornithine on Skin Conditions and Plasma IGF-1 Levels-A Randomized, Double-Blind, Placebo-Controlled Trial.
Randomized double‑blind placebo‑controlled pilot trial in 22 healthy adults given a fish‑derived collagen peptide plus ornithine drink (CPO) or placebo for 8 weeks; skin elasticity, transepidermal water loss and plasma IGF‑1 measured.
Related Ingredients
Other top-rated ingredients in Ergogenic Compounds.
Creatine Monohydrate
94/100A naturally occurring nitrogenous organic acid that facilitates recycling of adenosine triphosphate (ATP) in muscle and brain tissue via the phosphocreatine shuttle.
Maltodextrin
78/100Short-chain α-1,4 linked glucose polymer that is rapidly hydrolysed by brush-border maltase to glucose; near-equivalent glycaemic response to glucose but lower osmolality at concentration.
Cyclic Dextrin (HBCD)
72/100Produced via cyclic-glucanotransferase action on amylopectin, HBCD forms cluster-like macromolecules ~160 kDa that solubilise at low osmolality (≈4 mOsm/L) and clear the stomach faster than maltodextrin or glucose polymers.
Research Overview
Moderate EvidenceCite this ingredient
One-click citation export in APA, MLA, Chicago, BibTeX, or HTML. The URL below is stable and safe to link.
Stable URL
https://thesuppindex.com/ingredients/l-ornithine
SuppIndex. (2026). L-Ornithine: Evidence summary, dosage and clinical studies. Retrieved October 16, 2026, from https://thesuppindex.com/ingredients/l-ornithine
Based on 4 indexed studies · Evidence level: Moderate.
Goal Ratings
Stack Compatibility
Often combined with other compounds (e.g. collagen peptides) in studies; effects seen in composite products cannot be attributed solely to ornithine.