L-Ornithine

A urea-cycle amino acid with small data for exercise fatigue and stress-related sleep.

A structured monograph in Prometheus's bundled library. Its grades are the monograph's own reading of the evidence, not a peer-reviewed review.

2 at grade C — 2 graded rows

What is known

Each outcome with its grade (how strong the evidence is, A to D), the size of the effect where the entry records one, and how often studies agree.

Outcome	Grade	Effect size	Agreement
Exercise fatigueAmmonia clearance	Evidence grade C	Small	low
Stress / sleep markersSmall studies	Evidence grade C	Small	low

Read off the same rows as above. Nothing here is added that the entry does not itself record.

L-ornithine participates in the urea cycle, clearing ammonia; it is marketed for fatigue and stress.

By supporting ammonia detoxification it may reduce exercise fatigue, and it modestly lowers cortisol/stress markers in small studies.

Limited trials suggest reduced subjective fatigue and improved stress/sleep markers; performance effects are minor. Low-risk, low-yield.

2–6 g/day if trialing, often evening for stress.

Well tolerated; GI upset at high doses.

A minor anti-fatigue and stress option with thin evidence. Not essential.

As the entry records it, from the studies it summarises. Not a recommendation for you — doses that suit a trial population may not suit you.

Entries that share this one's tags or conditions.

L-Ornithine for Exercise fatigueEvidence grade C — Ammonia clearanceEvidence grade C
L-Ornithine for Stress / sleep markersEvidence grade C — Small studiesEvidence grade C
L-Ornithine: dosage and how to take it2–6 g/day.Evidence grade C
L-Ornithine: side effects, safety & interactionsWell tolerated; GI upset at high doses.Evidence grade C

This entry lists no references of its own.

Last revised Jul 10, 2026. A grade is this entry's reading of the evidence, not medical advice.