L-Ornithine

Ornithine · L-Ornithine hydrochloride

Snapshot

Indications	Contraindications
Stress-related fatigue^{1, 2} Sleep quality¹ Morning-after alcohol fatigue³ Circadian phase shift⁴	Gyrate atrophy of choroid and retina⁵ Pregnancy or nursing⁶

L-Ornithine is an amino acid that the body makes as an intermediate in the urea cycle, the pathway that disposes of ammonia, and it is a precursor of polyamines. It is also taken for fatigue the morning after alcohol, and for athletic performance and anabolic effect, where trials found no benefit. The typical patient is a healthy adult with work-related stress and fatigue.

A 2024 trial using a social stress test found no change in salivary cortisol but less fatigue and anger. In healthy adults, a 2018 placebo-controlled crossover trial found that supplementation delayed dim light melatonin onset, a marker of central circadian phase. Products are mostly capsules, with powders and tablets also sold, and 569 products list L-ornithine; see Form comparison.

A 2025 systematic review in healthy adults found gastrointestinal events were the main adverse effect, with no significant excess versus non-supplemented groups⁷. The retinal risk is the reason gyrate atrophy is a contraindication: a 2011 review links long-term, high blood ornithine to retinal toxicity and calls for blood ornithine and retinal evaluation in long-term high-dose users⁵.

Last updated October 17, 2026. Read how we make monographs.

In the full monograph

35 sources, 26 studies

When to useThe situations practitioners use it for, each with the reason and the study behind it.
SafetyWho should avoid it, who needs extra care, and the side effects reported in studies.
InteractionsThe medicines and supplements it interacts with, the effect of each, and what labeling says to watch.
Protocol notesThe doses used in studies, how and when they were taken, and how the forms on the market compare.
How it worksWhat it is and how it works in the body, in plain terms.
Published studiesThe studies behind each use, popular claims checked against them, and trials still under way.
Word of mouthWhat patients and practitioners report online, kept separate from the clinical evidence.
Clinical perspectiveA closing read of where the evidence is solid, where it is thin, and what has not been studied.

Snapshot

In the full monograph

Sources