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L-Ornithine
Accelerates ammonia clearance through the urea cycle, reducing exercise-induced fatigue and supporting recovery during prolonged efforts.
What the evidence says
Ornithine appears to help in 3 of 4 studies with measurable effects — the evidence leans clearly favourable.
Most evidence is from high-quality meta-analyses and randomised trials published 2007–2026 with a typical study size of 212 participants.
Based on 19 studies · 5 meta-analyses · 7 RCTs · 4,984 total participants
Confidence
HighWhat the studies found
By outcome
Ornithine has an evidence score of 8.5/10 — very strong evidence based on 19 indexed studies, including 16 meta-analyses. Accelerates ammonia clearance through the urea cycle, reducing exercise-induced fatigue and supporting recovery during prolonged efforts.
The commonly studied dose of Ornithine is 2-6g daily. Research points to an estimated optimal dose around 6g, with a minimum effective dose near 3g. Individual response varies — start low and adjust.
The best time to take Ornithine is before bed. It can be taken on an empty stomach. L-ornithine is a non-proteinogenic amino acid involved in the urea cycle.
Glycine
Likely helpsLowers core body temperature to deepen sleep — 3g before bed reduces daytime fatigue and boosts next-day cognition.
Arginine
Probably helpsPrimary substrate for nitric oxide production — dilates blood vessels to improve circulation, exercise performance, and cardiovascular health.
Last reviewed May 2026 · evidence from 38 studies · how we score
This information is for educational purposes only. It is not a substitute for professional medical advice. Always consult a qualified healthcare provider before starting, stopping, or changing any supplement or medication.
L-Ornithine is a non-protein amino acid that plays a central role in the urea cycle, helping the body eliminate ammonia. During intense or prolonged exercise, ammonia accumulates and contributes to fatigue. Ornithine supplementation may help clear ammonia more efficiently, reducing fatigue and supporting recovery. It's often combined with arginine for synergistic effects on growth hormone and exercise performance.
Accelerates ammonia detoxification
Helps clear exercise-induced ammonia buildup
May stimulate GH release when combined with arginine
How Ornithine works — from molecular targets to health outcomes. Click an edge to see supporting research.This visualization is in beta — pathways are being refined and expanded.
2-6g daily
Loading: Not required
Take with food
| Form | Type |
|---|---|
| 💊L-Ornithine HCl | Recommended |
| 💊L-Ornithine capsules | Alternative |
| 💊OKG (Ornithine Alpha-Ketoglutarate) | Alternative |
Often sold in combination with arginine. OKG may have enhanced effects.
Minimum: 2 weeks
Optimal: 8 weeks
Cycling: Not required
Note: Can be combined with arginine. For sleep benefits, take 30-60 minutes before bed.
Evidence specific to L-ornithine L-aspartate form in cirrhosis patients. Meta-analysis of 292 patients showed significant benefit vs placebo. GI adverse events noted as main side effect. Limited applicability to healthy populations.
Less ammonia-related exhaustion during exercise
Improved recovery between training sessions
May enhance sleep, especially after stress or exercise
May cause digestive upset at high doses
Limited data; consult healthcare provider
May benefit those with high ammonia production
Tip: Take with food; reduce dose
Tip: Reduce dose; divide into smaller doses
Ornithine is generally well-tolerated and considered safe for most healthy adults at recommended doses. The most commonly reported side effects are GI discomfort, diarrhea. Use caution if any of these apply to you: Severe kidney disease; Urea cycle disorders.
BCAAs
Probably helpsLeucine, isoleucine, and valine metabolized directly in muscle tissue — support protein synthesis and reduce exercise fatigue.
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