Protein & Amino Acids
L-Ornithine
An intermediate in the urea cycle that accelerates ammonia clearance during exercise, potentially reducing fatigue. Also used pre-sleep for growth hormone release.
Effective Dose
2–6g / day
per clinical evidence
Evidence Level
Limited
Protein & Amino Acids
Mechanism
Urea cycle intermediary, ammonia detoxification, GH release
primary action
Best For
Ammonia clearance
Endurance fatigue, Sleep
This profile is for informational purposes only and does not constitute medical advice. Consult a qualified healthcare professional before starting any supplementation, especially if you have pre-existing conditions or take medications.
What Is L-Ornithine?
Ornithine is a non-protein amino acid produced during arginine catabolism and is a key intermediate in the urea cycle, where it accepts carbamoyl phosphate to ultimately form urea for ammonia excretion. Elevated blood ammonia during prolonged exercise contributes to central fatigue — ornithine supplementation may accelerate clearance.
How It Works: The Science
Ornithine + carbamoyl phosphate → citrulline → arginine → urea (via arginase). This cycle detoxifies ammonia generated from amino acid catabolism during prolonged exercise. Faster ammonia clearance may reduce central fatigue signals. High doses of ornithine also stimulate growth hormone release, though this effect is modest.
Primary Mechanism
Urea cycle intermediary, ammonia detoxification, GH release
Evidence-Based Benefits
Dosage Guide
Effective Dose
2–6g / day
2–6g/day. For GH release: 5–10g on an empty stomach before sleep (less relevant for athletic performance). For endurance: 2–3g before prolonged exercise.
Safety Profile & Side Effects
Well tolerated. GI discomfort at very high doses (>10g). Safety well established as an amino acid naturally produced in the body.
Who Should (and Shouldn't) Take It
Endurance athletes experiencing significant fatigue in prolonged events (>90 minutes) and those interested in urea cycle support. Niche supplement — not a high-priority for most athletes.
Frequently Asked Questions
Related Ingredients
Medical Disclaimer
Ingredient profiles are for informational purposes only and do not constitute medical advice. Consult a qualified healthcare professional before starting any supplementation, especially if you have pre-existing conditions or take medications. Full disclaimer →