L-Ornithine
L-Ornithine is a non-proteinogenic amino acid that plays a role in the urea cycle, helping to clear ammonia and reduce exercise-induced fatigue. It may improve endurance performance and sleep quality, and is often used with arginine to enhance growth hormone secretion.
Evidence last reviewed: 20 Apr 2026
Moderate evidence supports L-ornithine's role in reducing fatigue and improving liver function. However, the evidence for its effects on growth hormone is limited and requires further investigation.
hepatic encephalopathy improvementpatients with cirrhosis · RCTModerate
L-ornithine L-aspartate improved hepatic encephalopathy grades and reduced inflammatory markers.
growth hormone secretionhealthy adults · RCTLow
L-ornithine, often combined with arginine, may enhance growth hormone secretion.
ammonia clearancepatients with chronic liver disease · RCTModerate
Intravenous L-ornithine L-aspartate improved grades of hepatic encephalopathy and reduced serum ammonia levels.
exercise-induced fatiguehealthy volunteers · RCTModerate
L-ornithine supplementation reduced physical fatigue by modulating lipid and amino acid metabolism.
Forms & usage▾
Take 3–6 grams daily, ideally before exercise or bedtime.