Overview
Urea-cycle amino acid that lowers fatigue and supports nighttime GH release.
- Dietary protein from animal sources (meat, fish, eggs, dairy) and plant sources (soy, legumes, grains)
- Free-form amino acid powders and capsules
- Targeted pre-workout, recovery, or sleep formulations
- Free-form crystalline powder
- Capsules or tablets
- Pre-mixed recovery or hydration beverages
- Time-release formulations
Mechanism of action
Detoxifies ammonia via urea cycle; combined with arginine for GH synergy.
- · Detoxifies ammonia via urea cycle
- · combined with arginine for GH synergy
Effects on the body
Organ system effects
L-Ornithine supports mitochondrial ATP production and fatigue resistance.
L-Ornithine promotes parasympathetic tone, GABAergic signaling, or melatonergic pathways that facilitate sleep onset and quality.
Evidence-based benefits
Reduces fatigue post-exercise
Limited evidencePotential side effects
- · L-Ornithine is generally well-tolerated at evidence-based doses
- · Mild GI discomfort (nausea, loose stools, or bloating) possible at higher intakes
- · Headache or transient fatigue reported by a small fraction of users
- · Allergic or hypersensitivity reaction (rash, itching, swelling)
- · Sleep disturbance if taken late in the day
- · Discontinue and seek medical advice if symptoms are severe, persistent, or include difficulty breathing
Drug interactions
Safety & non-supplemental interactions
Educational summary — always confirm with your clinician or pharmacist before starting, stopping, or combining with prescription therapy.
- ·Alcohol, benzodiazepines, opioids, sedating antihistamines (additive CNS depression)
Supplement interactions
- Magnesium glycinateComplementary GABAergic calming and improved sleep architecture.
- L-theanineReduces sleep latency without sedation.
No specific avoidances listed.
Dosing & bioavailability
Where to buy
Affiliate links — we may earn a commission at no extra cost to you. Amazon code supplementsch-20 is auto-applied at checkout. We don't endorse specific brands; verify third-party testing (USP, NSF, Informed Sport) before purchase.
Third-party testedIndependently verified L-Ornithine — look for USP, NSF, or Informed Sport seals on the label for purity and dose accuracy.L-Ornithine third party tested NSF
CapsulesPre-measured L-Ornithine capsules — easiest for travel and consistent daily dosing without scoops or scales.L-Ornithine capsules
PowderBulk unflavored L-Ornithine powder — best cost-per-gram and flexible dosing for stacking or mixing into drinks.L-Ornithine powder unflavored
Best sellersMost-purchased L-Ornithine products on Amazon — a quick way to see what's reviewed widely before you commit.L-Ornithine best sellerScientific evidence8Show studiesHide studies
Ornithine on fatigue and stress
Miyake M, et al.
8-week RCT of L-ornithine in subjects with fatigue.
Reduced fatigue and improved sleep quality.
PubMed: L-Ornithine — Reduces fatigue post-exercise
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PubMed: L-Ornithine — randomized controlled trial
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PubMed: L-Ornithine — meta-analysis
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PubMed: L-Ornithine — pharmacokinetics
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PubMed: L-Ornithine — safety adverse events
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PubMed: L-Ornithine — dose response
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Google Scholar: L-Ornithine — clinical evidence
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Cross-database citation index for L-Ornithine as it relates to "clinical evidence".
Includes preprints, theses, and journal articles. Useful for tracking citation counts and follow-on work.