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Amino Acid

L-Ornithine

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L-Ornithine. Urea-cycle amino acid that lowers fatigue and supports nighttime GH release.

How it works. Detoxifies ammonia via urea cycle; combined with arginine for GH synergy.

What the research supports. 1 graded claims. Strongest: Reduces fatigue post-exercise (limited).

How much to take. Typical dose: 2–6 g pre-bed.

Side effects and interactions. 1 medication interaction listed. Serious: Discontinue and seek medical advice if symptoms are severe, persistent, or include difficulty breathing.

Stacking. Pairs well with Magnesium glycinate, L-theanine.

Common forms. Available as Free-form crystalline powder, Capsules or tablets, Pre-mixed recovery or hydration beverages, Time-release formulations.

Key studies. 8 studies cited. The strongest are listed with links to PubMed.

Community. Experiences from people who have tried L-Ornithine. Anecdotes are not medical advice.

L-Ornithine. Urea-cycle amino acid that lowers fatigue and supports nighttime GH release.

Molecular structureC5H12N2O2 · 132.16 g/mol

What it is

Urea-cycle amino acid that lowers fatigue and supports nighttime GH release.

Food sources

Dietary protein from animal sources (meat, fish, eggs, dairy) and plant sources (soy, legumes, grains)Free-form amino acid powders and capsulesTargeted pre-workout, recovery, or sleep formulations

Goals

Growth Hormone SupportEnergy ProductionSleep & Recovery

How it works

Detoxifies ammonia via urea cycle; combined with arginine for GH synergy.

Pathways

  • Detoxifies ammonia via urea cycle
  • combined with arginine for GH synergy

Effects

  • ↓fatigue post-exercise decreases

What the research supports

Reduces fatigue post-exerciselimited

Strong: consistent results across large trials or meta-analyses. Moderate: several trials, mostly positive. Limited: small or mixed studies. Preclinical: animal or cell research only.

Typical dose
2–6 g pre-bed
TimingConsistent daily timing recommended; split larger doses if GI tolerance is a concern.
With foodEmpty stomach
Best formMost evidence is based on the free-form crystalline powder form.
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Side effects & interactions

Common 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

Serious

  • Discontinue and seek medical advice if symptoms are severe, persistent, or include difficulty breathing

Medication interactions

Prescription medications (general)minor

Always disclose L-Ornithine use to your prescriber — additive, antagonistic, or pharmacokinetic interactions are possible.

Check any supplement–medication combination with your pharmacist before starting.

Combines with

Pairs well

Common forms

  • Free-form crystalline powder
  • Capsules or tablets
  • Pre-mixed recovery or hydration beverages
  • Time-release formulations

Key studies

8 studies cited in total.

PubMed: L-Ornithine — Reduces fatigue post-exercise ↗
Systematic review · PubMed (NLM) · 2026

Opens current human and preclinical literature matching L-Ornithine and "Reduces fatigue post-exercise". Filter by RCT, meta-analysis, or year on the results page.

PubMed: L-Ornithine — randomized controlled trial ↗
Systematic review · PubMed (NLM) · 2026

Opens current human and preclinical literature matching L-Ornithine and "randomized controlled trial". Filter by RCT, meta-analysis, or year on the results page.

PubMed: L-Ornithine — meta-analysis ↗
Systematic review · PubMed (NLM) · 2026

Opens current human and preclinical literature matching L-Ornithine and "meta-analysis". Filter by RCT, meta-analysis, or year on the results page.

Discussion

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