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What is Ornithine?

Ornithine is an amino acid, but not one that is used to create proteins. It plays a role in the urea cycle, in conjunction with citrulline and arginine, two other amino acids.

Where Does Ornithine Come From?

Ornithine is produced within the body, from dietary sources of the essential amino acid l-arginine. This occurs during the aforementioned urea cycle. The urea cycle is a series of chemical reactions that happen within the body to detoxify nitrogen containing waste products.

Ornithine Health Benefits

Due its role in the breakdown of ammonia, ornithine is used as a treatment for diseases which involve a build up of the compound in bodily fluids. Hepatic encephalopathy is a disease of the liver that causes high blood concentrations of ammonia, which can adversely effect cognitive function. Ornithine has been demonstrated to significantly reduce the levels of ammonia, particularly at high doses.

Ornithine Benefits for Bodybuilding

A build up of ammonia in the muscles is a factor that can contribute to fatigue; supplementation with ornithine can attenuate this. It appears to reduce the subjective feelings of tiredness as well as allow a longer workout. In addition, several studies have demonstrated an increase in strength and power following several weeks of supplementation. One study found an increase in muscle mass over a period of 5 weeks, however it was supplemented in conjunction with another amino acid arginine, and so the results are confounded.

Ornithine may also increase levels of human growth hormone in the body by a significant percentage at high doses. However, the effects are temporary, and so continual supplementation may be needed to gain any benefit.

Ornithine is often used as a nitric oxide booster due to its link to the urea and nitric oxide cycles. This can increase blood flow, muscle pump, and effectiveness during a workout.

Ornithine Side Effects, Safety and Negatives

Large doses of ornithine may cause diarrhea. The active dose does appears to be much lower than the dose at which side effects start to occur, so there is a significant safety buffer. However, for effect on human growth hormone the levels do start to cross into the amount which may cause the gastrointestinal symptoms.

Ornithine Recommended Doses and Ingredient Timing

Ornithine is generally taken in the range of 2 to 6g each day. The benefits do appear to be dose dependent, meaning higher levels will have more of an effect. Up to 10g can be taken before gastrointestinal symptoms start to appear in susceptible individuals.

Ornithine Supplements

Ornithine can be bought as a stand alone amino acid, or is found in many pre and intra workouts and other nitric oxide boosters. These include Arnold Schwarzenegger Iron Pump, ASN Xtreme Pump and RedBak Nitric Stack.

Stacking Ornithine

Due to to its ability to attenuate fatigue and boost nitric oxide, ornithine may be well stacked with pre-workout supplements.


Demura S, et al. The effect of L-ornithine hydrochloride ingestion on performance during incremental exhaustive ergometer bicycle exercise and ammonia metabolism during and after exercise. Eur J Clin Nutr. (2010)
Grimble GK. Adverse gastrointestinal effects of arginine and related amino acids. J Nutr. (2007)
Mutch BJ, Banister EW. Ammonia metabolism in exercise and fatigue: a review. Med Sci Sports Exerc. (1983)
Zajac A, et al. Arginine and ornithine supplementation increases growth hormone and insulin-like growth factor-1 serum levels after heavy-resistance exercise in strength-trained athletes. J Strength Cond Res. (2010)
Sugino T, et al. L-ornithine supplementation attenuates physical fatigue in healthy volunteers by modulating lipid and amino acid metabolism. Nutr Res. (2008)

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