Ornithine
L-Ornithine
L-Ornithine is a non-protein amino acid that serves as a central intermediate in the urea cycle, playing a critical role in nitrogen disposal and ammonia detoxification. It is widely used as a supplement to promote growth hormone secretion, reduce exercise-induced fatigue, improve sleep quality, and support liver health. Ornithine is often paired with L-arginine or L-aspartate (as ornithine aspartate) to amplify its effects on ammonia clearance and anabolic signaling.
Mechanism of Action
Ornithine functions as the primary acceptor of carbamoyl phosphate in the hepatic urea cycle, facilitating the conversion of toxic ammonia into urea for excretion, thereby reducing blood ammonia levels during periods of high protein catabolism or intense exercise. It stimulates the pituitary release of growth hormone, likely through modulation of somatotroph activity and interactions with GABAergic pathways, which may contribute to its sleep-enhancing and anabolic effects. Additionally, ornithine serves as a precursor to polyamines (putrescine, spermidine, spermine) via ornithine decarboxylase, supporting cell proliferation and tissue repair.
Evidence by Health Goal(13 goals)
Dosing Protocols
30-45 minutes before bed on an empty stomach
Growth hormone-stimulating effects are most pronounced when taken fasted before sleep. Start at 2g to assess GI tolerance and titrate upward. For exercise fatigue reduction, 2g taken before exercise has shown efficacy in clinical trials. Ornithine HCl salt form provides approximately 80% elemental ornithine by weight.
Between meals or before and after exercise
Higher dose range used for ammonia detoxification support, particularly in liver disease contexts or heavy training. As ornithine aspartate (OA), 9g/day is a clinically studied dose for hepatic encephalopathy. GI side effects (nausea, diarrhea) become more likely above 6g/day.
Safety & Side Effects
L-Ornithine has a well-established safety profile at commonly used doses (2-6g/day) with the primary limiting factor being gastrointestinal tolerance. It is generally not associated with serious adverse effects in healthy individuals, though individuals with urea cycle disorders, severe liver disease, or renal impairment should use caution and consult a physician before supplementing.
Possible Side Effects
- !Gastrointestinal discomfort including nausea, cramping, and bloating at doses above 6g
- !Osmotic diarrhea at high single doses due to unabsorbed amino acid load
- !Transient drowsiness or sedation when taken before sleep (expected effect in some users)
- !Headache, particularly during initial use or at high doses
- !Mild hypotension in sensitive individuals due to nitric oxide pathway activation
- !Potential exacerbation of herpes simplex virus outbreaks with prolonged high-dose use (arginine-ornithine competition may shift balance)
- !Elevated urinary ornithine levels with potential for mild crystalluria at very high chronic doses
Interactions
- -May potentiate the effects of alcohol by accelerating acetaldehyde metabolism - concurrent use can alter intoxication patterns
- -Additive ammonia-lowering effects when combined with L-aspartate or lactulose - beneficial synergy but monitor in clinical liver disease management
- -May compete with L-arginine for intestinal absorption transporters - separate dosing by 1-2 hours when combining
- -Can enhance growth hormone-releasing effects of GHRH analogs or secretagogues - potential for amplified GH release
- -Use caution with antihypertensive medications as ornithine's nitric oxide precursor activity may produce additive blood pressure lowering
Cost & Where to Buy
Bulk powder forms (ornithine HCl) are the most cost-effective option at around $0.10-0.20 per gram. Capsule forms and branded ornithine aspartate formulations carry a premium. Monthly cost based on 2-4g daily dosing; higher therapeutic doses increase cost proportionally.
Search on Amazon