L-Ornithine – What is it, uses and benefits

L-Ornithine – What is it, uses and benefits

The amino acid L-ornithine is one of the most unknown substances in the field of sports. However, it has started to be used as a performance enhancer or hormone balance stimulant. Keep reading to find out more.

What is L-Ornithine?

In short, L-Ornithine is an amino acid bound to a carbon atom in isomer L-.

Above all, said amino acid is present in products like wild rice, Brazil walnuts and oregano, to name a few.

Our body produces ornithine too, in other words, it is a non-essential amino acid. Moreover, it is not a protein amino acid either because its synthesis takes place in the central part of the urea cycle. Therefore, it is an intermediary in this metabolic process.

According to this process, it is in charge of regulating the nitrogen excess. In addition, it is a precursor of citrulline and arginine. Above all, this is thanks to the enzyme Ornithine Transcarbamylase (OCT) in a localized processed in the mitochondria. That is why we need a proper functioning of the mitochondria for its synthesis.

Urea cycle

Figure I. Urea cycle with mediators and enzymatic reactions.

General uses of L-Ornithine

Ornithine is a relatively unknown amino acid in the field of sports. Although it has been studied as a sport performance enhancer and hormone stimulant. Moreover, it supports the urea cycle and the conversion of ammonia in urea for its later elimination.

Benefits of L-Ornithine

The scientific evidence that backs up the benefits of using this amino acid is quite limited.

At first, the focus was on the causes of a serum ornithine deficiency in the body. In fact, it can be fatal, causing hyperammonemia to the point that experiment animals (rats) died after 14 days. This was due to the excessive concentration of ammonia (Deignan et al. 2006)[1], a very toxic substance if we do not excrete it through the urine.

A conditional deficiency of ornithine is an extremely rare condition. However, depending on its degree, it could cause a dysfunction of the urea cycle. Consequently, it would increase the ammonia concentration, which is lethal.

Most of the causes of an ornithine deficiency in the body are: an excess of lysine, growth, pregnancy, traumas, extreme protein restriction (Zieve, 1986)[6]. Moreover, it can also be due to a deficiency of the enzymatic activity of any of the hormones involved in the urea cycle, usually OTC or OAT.
Otherwise, the arginine levels will increase while the ornithine ones drop drastically. The result is a deadly hyperammonemia due to a ornithine deficiency.

That is why ornithine supplementation is not as useful in this sense. Extreme traumas or enzymatic deficiencies are very serious and you should seek the help of a professional to treat them.

In case of suffering a conditional deficit, it should be enough to increase its intake in the diet.

L-Ornithine in sports

Ornithine has been widely used for bodybuilding without exactly knowing why. It was based on suppositions without any scientific evidence.

Certainly, the evidence about the use of ornithine is quite unclear and contradictory. Now we will discuss some essays with positive and negative results.

Studies and essays about L-Ornithine

First of all, there is a study by Ho et al. (2017)[2] where they gave L-Ornithine to rats by intraduodenal administration (not stomach or hypothalamus). They concluded that it increased the mRNA expression of Ghrelin which is the direct agonist of its receptor (involved in the production of the GH). Therefore, it also increased the plasma growth hormone levels considerably with doses of 24mMol/kg of L-Ornithine.

Intraduodenal administration

Figure II. Serum GH concentrations (ng/ml) in 5, 10, 15, 30 and 60’ after intraduodenal administration of a placebo vs 3mMol/kg of L-Ornithine vs 24mMol/kg of L-Ornithine in rats. (Ho et al. 2017)

After studies of this kind, scientists theorized a lot about the GH being sensitive to Ghrelin whose secretion is stimulated after taking L-Ornithine. However, in 1993, Labert et al. [4] already showed that taking 1.85g of L-Ornithine/L-Tyrosine orally (B) does not increase the serum HGH concentrations significantly.

hGH serum concentrations

Figure III. Serum concentrations of hGH (ng*min/ml) after oral intake of 1.85g of L-Ornithine+L-Tyrosine supplement in humans (column B) vs reference value (Placebo) vs 0.5mcg GHRH (column GHRH). (Lambert et al. 1993)

But we cannot conclude anything because the L-Ornithine dose is low and there are no studies with higher doses.

Less cortisol

Perhaps the most revealing study was the one by Miyake et al. (2014)[5], which gave 500mg of L-Ornithine monohydrochloride orally to 52 healthy individuals.

This study concluded that the markers analyzed such as DHEA-S increase, while cortisol dropped.

DHEA-S concentrations

Figure IV. Concentrations of DHEA-S, Cortisol and Ratio C:D for 8 weeks after taking L-Ornithine (black dots) vs placebo (white dots) (Miyake et al. 2014)

The emotional state of the participants improved too, which was assessed with the POMS scale.

POMS Mood Markers

Figure V. POMS Mood markers (A, Tension-Anxiety; B, Depression; C, Anger-Hostility; D, Vigor; E, Fatigue; F, confusion) for 8 weeks after taking L-Ornithine (dark dots) vs placebo (white dots) (Miyake et al. 2014)

Insomnia markers

In addition, they also assessed the quality of sleep with OSA-MA and the insomnia markers (AIS) improved considerably.

Quality of sleep markers

Figure VI. Quality of sleep markers OSA (A, Somnolence after waking up; B, Initiation and continuation of sleep; C, Frequent sleep; D, “recovery” after sleeping; E, Duration of sleep) for 8 weeks after taking L-Ornithine (dark dots) vs placebo (white dots) (Miyake et al. 2014)

Insomnia Marker

Figure VII. Insomnia Marker in the ISA scale for 8 weeks after taking L-Ornithine (dark dots) vs placebo (white dots) (Miyake et al. 2014)

Therefore, we can conclude that taking just 400mg of L-Ornithine daily improved the stress markers and quality of sleep.

Moreover, there are other studies that show similar results, such as the one by Kurata et al. (2012) [3] in animal models.


  1. Deignan, J. L., Livesay, J. C., Yoo, P. K., Goodman, S. I., O’Brien, W. E., Iyer, R. K., … Grody, W. W. (2006). Ornithine deficiency in the arginase double knockout mouse. Molecular Genetics and Metabolism, 89(1–2), 87–96. https://doi.org/10.1016/j.ymgme.2006.04.007
  2. Ho, Y. Y., Nakato, J., Mizushige, T., Kanamoto, R., Tanida, M., Akiduki, S., & Ohinata, K. (2017). l-Ornithine stimulates growth hormone release in a manner dependent on the ghrelin system. Food & Function, 8(6), 2110–2114. https://doi.org/10.1039/c7fo00309a
  3. Kurata, K., Nagasawa, M., Tomonaga, S., Aoki, M., Akiduki, S., Morishita, K., … Furuse, M. (2012). Orally administered L-ornithine reduces restraint stress-induced activation of the hypothalamic-pituitary-adrenal axis in mice. Neuroscience Letters, 506(2), 287–291. https://doi.org/10.1016/j.neulet.2011.11.024
  4. Lambert, M. I., Hefer, J. A., Millar, R. P., & Macfarlane, P. W. (1993). Failure of commercial oral amino acid supplements to increase serum growth hormone concentrations in male body-builders. International Journal of Sport Nutrition, 3(3), 298–305.
  5. Miyake, M., Kirisako, T., Kokubo, T., Miura, Y., Morishita, K., Okamura, H., & Tsuda, A. (2014). Randomised controlled trial of the effects of L-ornithine on stress markers and sleep quality in healthy workers. Nutrition Journal, 13, 53. https://doi.org/10.1186/1475-2891-13-53
  6. Zieve, L. (1986). Conditional deficiencies of ornithine or arginine. Journal of the American College of Nutrition, 5(2), 167–176.

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About Alfredo Valdés
Alfredo Valdés
He is a specialist in metabolic physiopathology training and in the biomolecular effects of food and physical exercise.
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