Evidence supporting the use of: L-ornithine
For the health condition: Athletic and Exercise Aids

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Synopsis

Source of validity: Scientific
Rating (out of 5): 2

L-ornithine is a non-proteinogenic amino acid that plays a role in the urea cycle, helping to remove ammonia from the body, which is a byproduct of protein metabolism and exercise. Its use as an athletic and exercise aid is primarily based on its theoretical ability to reduce fatigue and enhance recovery by supporting ammonia clearance. Several small-scale clinical studies have investigated l-ornithine supplementation in athletes and physically active individuals. Some studies have shown that l-ornithine supplementation (typically 2–8 grams per day) may reduce perceived fatigue, improve recovery time, and decrease post-exercise levels of ammonia. For example, a 2008 randomized, double-blind, placebo-controlled study found that L-ornithine supplementation reduced fatigue in healthy volunteers undergoing physical exercise, likely due to its effect on ammonia metabolism. However, the overall body of evidence is limited by small sample sizes, short duration, and variability in study design and dosing. Meta-analyses and systematic reviews are lacking, and there is insufficient evidence to recommend l-ornithine as a definitive ergogenic aid. While some athletes use it for potential recovery benefits, current scientific validation is modest, and more robust trials are needed to confirm its efficacy. Thus, the evidence supporting l-ornithine for athletic performance and exercise recovery is preliminary and rates a 2 on a 0–5 scale.

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