Ornithine
Summary
L-ornithine is an amino acid the body uses to clear ammonia. Small Japanese trials found 400–1,600 mg/day eased self-rated stress, fatigue and sleep complaints (grade D), but cortisol results were inconsistent and most trials came from one manufacturer's corporate group. Exercise combinations showed little performance benefit. L-ornithine L-aspartate, studied in cirrhosis, is a different product.
Key facts
- Kirin group researchers ran the stress, sleep and alcohol trials with ornithine from Kirin affiliates; Kao Co., Ltd. funded the lead author of a catechin-ornithine trial[1][2][5][6]
- L-ornithine L-aspartate (LOLA) is a separate product studied in people with cirrhosis[8]
- 6 graded human outcomes on this page
- October 10, 2026
How it works
ProposedOrnithine is an intermediate of the urea cycle, which clears ammonia from the body. Trial authors propose that extra ornithine supports ammonia clearance and energy use during exercise and lowers the stress hormone cortisol, but measured effects on ammonia and cortisol have been inconsistent.[3][6][1][2]
What the human research says
Human trials only, one row per outcome. The form column shows what each trial actually tested. Grades follow our evidence-grading policy.
At a glance: strongest evidence per outcome
| Outcome | Grade | Effect | Strongest evidence | Rows |
|---|---|---|---|---|
| Stress | Grade D | Mixed | RCT · n = 65 · 2024 | 1 row |
| Stress and sleep | Grade D | Improved | RCT · n = 52 · 2014 | 1 row |
| Fatigue | Grade D | Improved | Crossover RCT · n = 17 · 2008 | 2 rows |
| Exercise | Grade D | Improved | RCT · n = 17 · 2010 | 2 rows |
Every graded row
| Outcome | Effect | Grade | Best evidence | PMID |
|---|---|---|---|---|
| Cortisol, fatigue and mood after a social stress test | Mixed | Grade D | RCT · n = 65 · 2024 Healthy adults (Japan) Form: L-ornithine · Dose: 1,600 mg/day, plus a dose 1 hour before the test · Duration: 7 days No effect on saliva cortisol. Fatigue-inertia and anger-hostility mood scores the morning after the stress test were better than with placebo. | 39768508 (opens PubMed)Source [2] |
| Stress hormones, mood and perceived sleep quality | Improved | Grade D | RCT · n = 52 · 2014 Healthy Japanese adults who felt slight stress and fatigue Form: L-ornithine monohydrochloride · Dose: 400 mg/day · Duration: 8 weeks Serum cortisol and the cortisol/DHEA-S ratio fell versus placebo; anger scores fell and perceived sleep quality improved. | 24889392 (opens PubMed)Source [1] |
| Feelings of fatigue and sprint performance during prolonged cycling | Improved | Grade D | Crossover RCT · n = 17 · 2008 Healthy volunteers Form: L-ornithine hydrochloride · Dose: 2,000 mg/day for 7 days, then 6,000 mg on day 8 · Duration: 8 days per period Fatigue ratings after recovery were lower than right after the exercise load (P<.01), and lower than placebo in women (P<.05). The fall in 10-second maximum pedaling speed over the session was smaller than with placebo. | 19083482 (opens PubMed)Source [3] |
| Growth hormone and IGF-1 after resistance exercise (with arginine) | Improved | Grade D | RCT · n = 17 · 2010 Experienced strength-trained athletes Form: L-arginine plus L-ornithine · Dose: Not stated in the abstract · Duration: 3 weeks of heavy-resistance training Growth hormone and IGF-1 were higher after exercise in the supplemented group; resting hormones, testosterone, cortisol and insulin did not differ from placebo. | 20300016 (opens PubMed)Source [7] |
| Blood ammonia and cycling performance (with tea catechins) | No effect | Grade D | Crossover RCT · n = 16 · 2025 Healthy young men Form: Tea catechins plus ornithine · Dose: Single dose and 14 days of daily intake (amounts not stated in the abstract) · Duration: 14 days per period No effect on exercise-induced ammonia or on power output in a 15-minute cycling test; perceived fatigue during 60 minutes of cycling was lower than with placebo. | 40506665 (opens PubMed)Source [6] |
| Next-morning fatigue and mood after drinking alcohol | Improved | Grade D | Crossover RCT · n = 11 · 2013 Healthy Japanese adults with the alcohol flushing trait Form: L-ornithine monohydrochloride · Dose: 400 mg once, 30 minutes after alcohol (0.4 g/kg) · Duration: One night per condition Next-morning fatigue, lassitude, anger-hostility and confusion scores fell, reported sleep length rose and waking saliva cortisol was lower than with placebo. Alcohol metabolism did not change. | 23414576 (opens PubMed)Source [5] |
Forms
| Form | Elemental % | Absorption (human data) | GI tolerance | Studied for |
|---|---|---|---|---|
| L-ornithine hydrochloride (monohydrochloride) | Varies[1][2][3][5] | No human absorption data in our sources.[3] | The trial abstracts cited here report no adverse effects at 400–6,000 mg/day over 1–8 weeks.[1][2][3] | Stress, sleep and fatigue trials (400–6,000 mg/day) |
| L-ornithine L-aspartate (LOLA) | Varies[8] | Given by mouth or intravenously in cirrhosis trials; no head-to-head absorption data in our sources.[8] | Non-serious adverse events did not differ from placebo or no intervention across 14 trials.[8] | Hepatic encephalopathy trials in people with cirrhosis |
| Ornithine combined with arginine or tea catechins | Varies[6][7] | Plasma ornithine rose after a catechin-ornithine product.[6] | No adverse effects reported in the abstracts.[6][7] | Exercise and hormone studies |
Studied doses
Doses studied in human trials ranged from 400 mg/day for 8 weeks to 2,000 mg/day for a week, with one trial adding a single 6,000 mg day. Stress and sleep studies used 400–1,600 mg/day.[1][2][3]
Interactions
Published interactions only: each row cites a source. No row means none was found in our sources, not that a combination is safe.
None found in our sources.
Who should be careful
- Gyrate atrophy of the choroid and retina
- This rare inherited disorder already causes very high blood ornithine levels, and its treatments aim to act on the ornithine pathway; ornithine supplements run counter to that goal and need input from the specialist managing it.[9]
- Liver disease
- L-ornithine L-aspartate is studied for hepatic encephalopathy in cirrhosis under medical supervision; that evidence does not apply to self-use of ornithine supplements.[8]
Talk to your pharmacist or clinician before starting a supplement, especially if you take prescription medicines.
Safety
Short trials report no safety problems in their abstracts.
- Side effects
- None reported in the abstracts of the stress, sleep and fatigue trials cited here (400–6,000 mg/day).[1][2][3]
- LOLA trials
- Across 14 trials in cirrhosis, non-serious adverse events with L-ornithine L-aspartate did not differ from placebo or no intervention.[8]
- Long-term data
- The longest ornithine trial cited here lasted 8 weeks.[1]
How to read the label
- Label dose vs clinical doseJapanese stress and sleep trials used 400 mg/day of L-ornithine; a physical-fatigue trial used 2,000 mg/day.[1][3]
- Salt formTrials dosed L-ornithine as the hydrochloride (monohydrochloride) salt.[1][3]
- LOLA is a different productL-ornithine L-aspartate is a separate compound tested by mouth and intravenously in people with cirrhosis.[8]
Cost per studied dose, without the sales pitch
Compare any product you already have by the amount it delivers, not by capsule count or front-of-pack weight.
Cost per studied dose
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Frequently asked questions
Does ornithine help you sleep?
One 8-week trial in 52 mildly stressed Japanese adults found better perceived sleep quality with 400 mg/day. Researchers from the manufacturer's corporate group ran it.[1]
Does ornithine lower stress?
It lowered cortisol in that 8-week trial but not around a social stress test, where only next-morning fatigue and anger scores improved.[1][2]
Does ornithine help after drinking alcohol?
In 11 Japanese adults with the flushing trait, 400 mg after drinking eased next-morning fatigue and lowered waking cortisol; alcohol metabolism did not change.[5]
Does ornithine build muscle or boost growth hormone?
With arginine it raised growth hormone and IGF-1 after training in 17 athletes, but strength was not reported; with tea catechins it did not improve cycling performance.[7][6]
Is ornithine the same as L-ornithine L-aspartate?
No. LOLA is a separate compound studied in cirrhosis, and a Cochrane review rated that evidence very low quality.[8]
Does ornithine affect the body clock?
In 28 healthy adults, 400 mg/day for 7 days delayed evening melatonin onset by about 15 minutes; the abstract reports no sleep outcomes.[4]
Sources
- [1]Randomised controlled trial of the effects of L-ornithine on stress markers and sleep quality in healthy workers.. Nutr J, 2014. RCT
- [2]Effects of Oral Ingestion of L-Ornithine on Mental Stress and Fatigue Based on the Trier Social Stress Test in Healthy Humans: A Randomized, Double-Blind, Placebo-Controlled, Parallel-Group Trial.. J Clin Med, 2024. RCT
- [3]L-ornithine supplementation attenuates physical fatigue in healthy volunteers by modulating lipid and amino acid metabolism.. Nutr Res, 2008. crossover-RCT
- [4]A randomized, double-blind and placebo-controlled crossover trial on the effect of l-ornithine ingestion on the human circadian clock.. Chronobiol Int, 2018. crossover-RCT
- [5]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.. Biopsychosoc Med, 2013. crossover-RCT
- [6]The effects of acute and chronic oral tea catechins and ornithine supplementation on exercise-induced ammonia accumulation and cycling performance in healthy young men: a randomized, double-blind, cross-over, placebo-controlled trial.. Eur J Appl Physiol, 2025. crossover-RCT
- [7]Arginine and ornithine supplementation increases growth hormone and insulin-like growth factor-1 serum levels after heavy-resistance exercise in strength-trained athletes.. J Strength Cond Res, 2010. RCT
- [8]L-ornithine L-aspartate for prevention and treatment of hepatic encephalopathy in people with cirrhosis.. Cochrane Database Syst Rev, 2018. systematic-review
- [9]A review of treatment modalities in gyrate atrophy of the choroid and retina (GACR).. Mol Genet Metab, 2021. systematic-review
What changed
- First draft. Every PMID checked against NCBI E-utilities esummary (title and year taken from the record) and abstracts read for the cited rows.
- Adversarial review pass: every evidence row re-read against its PubMed abstract. No NIH ODS or NCCIH fact sheet covers ornithine, so no official monograph is cited. Industry ties: Kirin group researchers ran the 2014, 2013 and 2024 trials with ornithine from Kirin affiliates (PMC4055948, PMC3583691, PMC11676746); Kao Co., Ltd. funded the corresponding author of the 2025 catechin trial; funding for the 2008 and 2010 trials is not stated in PubMed. Retraction, expression-of-concern, erratum and withdrawn checks on all 9 PMIDs: none flagged. Page set indexable. Independent browser review (4 parallel reviewers, every evidence row checked against its abstract and official sources on the Vercel preview) found: industry-ties key fact now names the Kao grant; gyrate atrophy caution made explicit.