Supplement

Ornithine

Ornithine is an amino acid the body makes as part of the urea cycle, the process that helps clear ammonia from the blood. Researchers have looked at it for stress hormones, but the evidence is limited: a single crossover trial in 27 people found mixed results for cortisol. Other small work in 15 people also found mixed results for ammonia and no clear difference in blood pressure, so the picture is thin.

Sources: PMID 23414576

Updated 30 September 2026
How we grade
3 studies cited

Best evidence: Grade C
Conditions studied: 3
Outcomes: 16
Graded outcomes: 0031

Evidence by condition

Strong
Moderate
Limited
Very limited

3 conditions

Metabolic Health

Metabolic Health: outcomes studied for Ornithine
Grade	Outcome	Effect	Studies	People
	Cortisol Mixed effect		1 study	27 people
Studies that measured cortisol A randomized, double-masked, placebo-controlled crossover trial on the effects of L-ornithine on salivary cortisol and feelings of fatigue of flushers the morning after alcohol consumptionBiopsychosoc Med · PMID 23414576
	Fatigue Symptoms	Improves (the measure goes down)		27 people
	Sleep Quality	Improves (the measure goes up)		27 people

Fatigue

Fatigue: outcomes studied for Ornithine
Grade	Outcome	Effect	Size	Studies	People
	Ammonia Mixed effect				15 people
	Blood Pressure No effect		NoneNo effect		15 people
	Cortisol	Improves (the measure goes down)		1 study	27 people
Studies that measured cortisol A randomized, double-masked, placebo-controlled crossover trial on the effects of L-ornithine on salivary cortisol and feelings of fatigue of flushers the morning after alcohol consumptionBiopsychosoc Med · PMID 23414576
	Heart Rate	Improves (the measure goes down)		1 study	30 people
Studies that measured heart rate L-ornithine supplementation attenuates physical fatigue in healthy volunteers by modulating lipid and amino acid metabolismNutr Res · PMID 19083482
	Fatigue Symptoms	Improves (the measure goes down)			42 people
	Sleep Quality	Improves (the measure goes up)			27 people
	Training Volume	Improves (the measure goes up)			15 people
	Urea	Improves (the measure goes up)			15 people

Cycling Performance

Cycling Performance: outcomes studied for Ornithine
Grade	Outcome	Effect	Studies	People
	Ammonia Mixed effect			14 people
	Anaerobic Capacity	Improves (the measure goes up)	1 study	14 people
Studies that measured anaerobic capacity The effect of L-ornithine hydrochloride ingestion on performance during incremental exhaustive ergometer bicycle exercise and ammonia metabolism during and after exerciseEur J Clin Nutr · PMID 20717126
	Heart Rate	Improves (the measure goes down)	1 study	14 people
Studies that measured heart rate L-ornithine supplementation attenuates physical fatigue in healthy volunteers by modulating lipid and amino acid metabolismNutr Res · PMID 19083482
	Oxygen Uptake	Improves (the measure goes up)		14 people
	Urea	Improves (the measure goes up)		14 people

Key findings

CortisolMetabolic Health
AmmoniaFatigue
Blood PressureFatigue

Shop Ornithine

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Grade C

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Studies cited

3 studies from PubMed

A randomized, double-masked, placebo-controlled crossover trial on the effects of L-ornithine on salivary cortisol and feelings of fatigue of flushers the morning after alcohol consumptionBiopsychosoc Med · PMID 23414576
L-ornithine supplementation attenuates physical fatigue in healthy volunteers by modulating lipid and amino acid metabolismNutr Res · PMID 19083482
The effect of L-ornithine hydrochloride ingestion on performance during incremental exhaustive ergometer bicycle exercise and ammonia metabolism during and after exerciseEur J Clin Nutr · PMID 20717126