L-Ornithine
L-Ornithine
TL;DR
L-ornithine is a urea-cycle amino acid marketed for sleep and exercise recovery. The most credible evidence is small trials showing reduced ammonia and improved sleep quality in stressed adults.
Ideal For
- Endurance athletes doing long sessions where ammonia builds up
- Adults with stress-related poor sleep quality wanting a low-risk trial
Avoid If
- You have significant kidney impairment
- You are pregnant or breastfeeding — no safety data
Frequently Asked Questions
What is L-ornithine?
Does it improve sleep or stress?
Does it reduce exercise fatigue?
Does it raise growth hormone?
How does it compare with ornithine alpha-ketoglutarate?
Is it safe?
Overview
L-ornithine is not a protein-building amino acid — it exists as an intermediate in the urea cycle, where it accepts carbamoyl groups on the way to disposing of ammonia as urea. That single function explains most of the plausible use cases. Ammonia accumulates during intense endurance exercise and contributes to central fatigue, and it is elevated in liver dysfunction, where the related compound L-ornithine L-aspartate (LOLA) has genuine clinical evidence for hepatic encephalopathy. For healthy people, the interesting result is a small Japanese randomized trial in which 400 mg/day of ornithine for eight weeks improved subjective sleep quality and lowered cortisol-to-DHEA ratio in adults reporting fatigue. It is a modest, single-population finding rather than a robust effect. Claims that ornithine raises growth hormone come from intravenous infusion studies at doses far beyond oral supplementation, and oral doses large enough to shift GH cause diarrhea before they change body composition. Ornithine is reasonable to try for sleep or post-exercise ammonia; it is not a growth-hormone strategy.
How It Works
- Accepts carbamoyl phosphate in the urea cycle, accelerating ammonia clearance
- Converted to citrulline and then arginine, feeding nitric oxide production indirectly
- Reduces exercise-induced ammonia accumulation implicated in central fatigue
- Precursor to polyamines involved in tissue repair
Benefits & Outcomes
No linked outcomes yet. Research is ongoing.
Supporting Research6 studies
Arginine and ornithine supplementation increases growth hormone and insulin-like growth factor-1 serum levels after heavy-resistance exercise in strength-trained athletes
Zajac A, Poprzecki S, Zebrowska A +2 more
Three weeks of L-arginine plus L-ornithine during heavy resistance training raised post-exercise GH and IGF-1 concentrations versus placebo.
L-ornithine L-aspartate for prevention and treatment of hepatic encephalopathy in people with cirrhosis
Goh ET, Stokes CS, Sidhu SS
L-ornithine L-aspartate may benefit hepatic encephalopathy, but the evidence is of very low certainty.
Randomised controlled trial of the effects of L-ornithine on stress markers and sleep quality in healthy workers
Miyake M, Kirisako T, Kokubo T
L-ornithine 400 mg/day reduced the cortisol to DHEA-S ratio and improved sleep quality scores versus placebo.
L-Ornithine supplementation attenuates physical fatigue in healthy volunteers by modulating lipid and amino acid metabolism
Sugino T, Shirai T, Kajimoto Y
L-ornithine reduced subjective fatigue and serum ammonia accumulation during exercise compared with placebo.
The effect of L-ornithine hydrochloride ingestion on performance during incremental exhaustive ergometer bicycle exercise and ammonia metabolism during and after exercise
Demura S, Yamada T, Yamaji S
L-ornithine did not improve exhaustive cycling performance despite altering post-exercise ammonia metabolism.
A randomized, double-masked, placebo-controlled crossover trial on the effects of L-ornithine on salivary cortisol and feelings of fatigue of flushers the morning after alcohol consumption
Kokubo T, Ikeshima E, Kirisako T
A single dose of L-ornithine lowered salivary cortisol and self-reported fatigue.
Safety Information
Potential Side Effects
Osmotic diarrhea, cramping and nausea at doses above roughly 10 g. Well tolerated at the 400 mg to 6 g range.
Contraindications
Severe renal impairment.
Drug Interactions
- No well-documented interactions at supplement doses
Pregnancy & Breastfeeding
Pregnancy: Not enough evidence to judge
Breastfeeding: Not enough evidence to judge
Dosage Guidelines
Dosage Used in Studies
Consult healthcare provider
Dosing by Goal
| Goal | Dose | Notes |
|---|---|---|
| Exercise ammonia | 2-6 g before endurance exercise | |
| Sleep and stress | 400 mg daily in the evening for 8 weeks | |
| Notes | Doses above 10 g commonly cause diarrhea |
Forms Compared
L-ornithine HCl
Standard supplement form
Ornithine alpha-ketoglutarate (OKG)
Used in clinical nutrition for wound healing and catabolic states
L-ornithine L-aspartate (LOLA)
The form with clinical evidence in hepatic encephalopathy
Food & Timing
Evening on an empty stomach for sleep use; 30-60 minutes pre-exercise for ammonia buffering.
Medical Disclaimer
The information provided on this website is for educational and informational purposes only and is not intended as a substitute for professional medical advice, diagnosis, or treatment. Always seek the advice of your physician or other qualified health provider with any questions you may have regarding a medical condition or before starting any supplement regimen.
Individual results may vary. The statements on this website have not been evaluated by the Food and Drug Administration. Products and information are not intended to diagnose, treat, cure, or prevent any disease.