L-Ornithine
EVIDENCE: WEAKAlso sold as: ornithine, L-ornithine HCl, L-ornithine hydrochloride
Ornithine is an amino acid in the body's ammonia-clearing urea cycle. Small Japanese trials found 400 mg a day for 8 weeks eased fatigue and improved sleep quality in stressed workers, and gram doses lessened exercise fatigue.
Compiled by iSupplementReviews editorial team ·Researched 2026-10-16 · 3 sources
- Type
- Amino acid (urea cycle)
- Studied dose
- 400 mg/day (stress and sleep); 2,000–6,000 mg/day (exercise fatigue)
- Best form
- L-ornithine hydrochloride
- Our rating
- WEAK — Mostly small, animal, or traditional evidence
What is L-ornithine?
L-ornithine is an amino acid that helps the liver convert toxic ammonia into urea. It is not used to build proteins and is sold for fatigue, sleep and recovery.
Other names and forms
Ornithine, L-ornithine HCl. Ornithine aspartate (LOLA) is a related medicine used for liver disease in some countries.
Where does L-ornithine come from?
The body makes it from arginine. Freshwater clams (shijimi) are a notable food source in Japan.
How does L-ornithine work in the body?
By supporting ammonia clearance, ornithine may reduce one contributor to fatigue during exercise. The ammonia-lowering role is best shown in liver disease, where the related medicine L-ornithine L-aspartate is studied at several grams a day (He et al., 2024). Effects on sleep and stress hormones are proposed from small trials.
What is L-ornithine claimed to do?
Reduce fatigue, improve sleep, support liver function and exercise recovery.
What does the research show?
| Claim | Evidence | Dose studied | Verdict |
|---|---|---|---|
| Stress markers and sleep quality | One small RCT | 400 mg/day, 8 weeks | Early positive |
| Exercise fatigue | Small crossover trial | 2–6 g | Early positive |
| Blood sugar or hearing | None | — | Not studied |
Sleep and stress
One 8-week trial found 400 mg a day improved sleep quality and lowered cortisol in tired workers. Miyake et al. (2014) ran a randomized, placebo-controlled trial in healthy Japanese workers with mild stress and fatigue.
Exercise fatigue
Gram doses reduced feelings of fatigue after exercise in a small crossover study. Sugino et al. (2008) tested 2 g a day for 7 days and 6 g on the exercise day in 17 healthy volunteers.
What dose was studied?
| Goal | Dose | Duration |
|---|---|---|
| Sleep and stress | 400 mg/day | 8 weeks |
| Exercise fatigue | 2,000–6,000 mg/day | Up to 8 days |
Side effects
Stomach upset and diarrhea at higher doses.
Drug interactions
None well documented at supplement doses.
Who should not take L-ornithine?
People with rare urea-cycle or ornithine-metabolism disorders, and those who are pregnant (no data).
What the authorities say
No regulator approves ornithine for fatigue or sleep. It is a normal metabolic amino acid.
What to know about L-ornithine
Small trials suggest ornithine may help fatigue and sleep at 400 mg to several grams a day. The evidence is preliminary.
Frequently asked questions about L-Ornithine
What does L-ornithine do?
It helps the body clear ammonia. Small trials suggest it may ease fatigue and improve sleep quality, but the studies are few and small.
Does ornithine help sleep?
One 8-week trial in Japanese workers who reported fatigue found 400 mg a day improved subjective sleep quality and lowered stress markers compared with placebo.
Is ornithine safe?
Doses up to several grams a day were well tolerated in short trials; stomach upset is the most common complaint.
References
- [1]Miyake M et al. — Randomised controlled trial of the effects of L-ornithine on stress markers and sleep quality in healthy workers (Nutr J, 2014)
- [2]Sugino T et al. — L-ornithine supplementation attenuates physical fatigue in healthy volunteers by modulating lipid and amino acid metabolism (Nutr Res, 2008)
- [3]He Q et al. — Efficacy of L-ornithine L-aspartate for minimal hepatic encephalopathy in patients with cirrhosis: a systematic review and meta-analysis (Arab J Gastroenterol, 2024)
Products we reviewed containing L-Ornithine
Based on recorded labels or seller-described formulas. Inclusion does not establish a match to the strains, preparations or amounts studied here; check each review's disclosure limits.