L-Ornithine is an amino acid acting primarily in the urea cycle, which eliminates excess nitrogen from the body. It is also very important in the removal of ammonia (NH3), a waste product of cellular metabolism, from your body.

L-Ornithine stimulates the secretion of growth hormones. (1) L-Ornithine supplementation has the potential to relieve stress and to improve sleep quality related to fatigue, both objectively and subjectively. (2) A study showed that an intracerebroventricular (i.c.v.) injection of L-Ornithine attenuated the stress response in neonatal chicks. (3) These actions were suggested to be mediated by the gamma-aminobutyric acid (GABA) receptor. A serotonin metabolite (5-hydroxyindole acetic acid, 5-HIAA) was induced in the striatum after L-Ornithine supplementation. So day-time serotonin levels stimulate the production of melatonin during the night, therefore, L-Ornithine might be considered an important nutrient to maintain the circadian rhythm and to allow individuals to sleep well. As research has shown there is a correlation between night-time growth hormone release and sleep satisfaction. L-Ornithine administration stimulated the release of growth hormone, which is secreted as the largest pulse after the onset of sleep. (4) 

Some evidence suggests that ornithine increases endurance and accelerates recovery after exercise. (5) In two clinical studies, subjects taking ornithine recovered faster from exercise and reported feeling less fatigued. In one of these, ornithine appeared to increase people’s anaerobic (burst, sprint, or strength) performance. A combination of L-Ornithine and L-Aspartate may increase mental sharpness during physical exercise. (6) Also supplementing with L-Ornithine and L-Aspartate (LOLA) has prevented episodes of HE in cases of chronic liver disease. LOLA decreased blood ammonia and improves cognitive symptoms, even in people with severe end-stage disease. (7) Some researchers have suggested that people with chronic liver disease, even those who don’t have obvious cognitive symptoms, may benefit from supplementing with LOLA. (8) Ornithine and alpha-ketoglutarate (OAK) may protect muscle protein building in times of high stress, such as after a surgery. (9) 

One study compared blood growth hormone level before L-Ornithine hydrochloride ingestion, 45 minutes and 90 minutes after ingestion under the conditions of 40, 100 and 170 mg/kg body-mass ingestion using bodybuilders. The bodybuilders reported that blood growth hormone level at 90 minutes after ingestion in the 170 mg/kg condition was significantly greater than that of the other conditions (about 150-300%), and also significantly greater than that before ingestion (about 350%). Also increasing the amount of growth hormone level before ingestion to 30 minutes after strength training was also significantly greater in subjects ingesting L-Ornithine hydrochloride than in those ingesting the placebo. The difference was considerable (about 200%). (10) Another study showed that the intraduodenal administration of L-Ornithine (L-Orn) stimulates growth hormone (GH) secretion in wistar rats through the sympathetic nervous and ghrelin systems. (1) 

References: 

1. Ho YY, Nakato J, Mizushige T, Kanamoto R, Tanida M, Akiduki S, Ohinata K. l-Ornithine stimulates growth hormone release in a manner dependent on the ghrelin system. Food Funct. 2017 Jun 1; 8 (6): 2110-2114. 

2. Miyake M, Kirisako T, Kokubo T, Miura Y, Morishita K, Okamura H, Tsuda A. Randomised controlled trial of the effects of L-ornithine on stress markers and sleep quality in healthy workers. Nutr J. 2014 Jun 3; 13:53. 

3. Kurata K, Nagasawa M, Tomonaga S, Aoki M, Akiduki S, Morishita K, Denbow DM, Furuse M. Orally administered L-ornithine reduces restraint stress-induced activation of the hypothalamic-pituitary-adrenal axis in mice. Neurosci Lett. 2012 Jan 11; 506 (2): 287-91. 

4. Davidson JR, Moldofsky H, Lue FA. Growth hormone and cortisol secretion in relation to sleep and wakefulness. J Psychiatry Neurosci. 1991 Jul; 16 (2): 96-102. 

5. Demura S, Morishita K, Yamada T, Yamaji S, Komatsu M. Effect of L-ornithine hydrochloride ingestion on intermittent maximal anaerobic cycle ergometer performance and fatigue recovery after exercise. Eur J Appl Physiol. 2011 Nov; 111 (11): 2837-43. 

6. Mikulski T, Dabrowski J, Hilgier W, Ziemba A, Krzeminski K. Effects of supplementation with branched chain amino acids and ornithine aspartate on plasma ammonia and central fatigue during exercise in healthy men. Folia Neuropathol. 2015; 53 (4): 377-86. 

7. Mikulski T, Dabrowski J, Hilgier W, Ziemba A, Krzeminski K. Effects of supplementation with branched chain amino acids and ornithine aspartate on plasma ammonia and central fatigue during exercise in healthy men. Folia Neuropathol. 2015; 53 (4): 377-86. 

8. Abhijeet Waghray, Nisheet Waghray, Kevin Mullen. Management of Covert Hepatic Encephalopathy J Clin Exp Hepatol. 2015 Mar; 5 (Suppl 1): 75–81. 

9. J Wernerman, F Hammarqvist, A von der Decken, E Vinnars. Ornithine-alpha-ketoglutarate improves skeletal muscle protein synthesis as assessed by ribosome analysis and nitrogen use after surgery. Ann Surg. 1987 Nov; 206 (5): 674–678. 

10. Demura S, Yamada T, Yamaji S, Komatsu M, Morishita K. The effect of L-ornithine hydrochloride ingestion on human growth hormone secretion after strength training. Advances in Bioscience and Biotechnology. 2010 Jan; 01 (01): 7-11