Larginine

L-arginine is an α-amino acid that is one of the 20 standard amino acids used by organisms to synthesize proteins. The naturally occurring, protein-incorporated form in humans is the L-enantiomer. It is considered semi-essential or conditionally essential because the body typically makes enough for normal function, but certain life stages and medical conditions can increase the required amount.

In metabolism, arginine has several roles. It is a substrate for nitric oxide synthase, producing nitric oxide, a signaling molecule that acts as a vasodilator involved in regulating blood flow and blood pressure. It participates in the urea cycle, where it is converted to ornithine and urea to help dispose of excess nitrogen. Arginine also contributes to the synthesis of creatine, proline, polyamines, and other metabolites, and it supports immune function and wound healing.

Dietary sources of arginine include meat, fish, eggs, dairy products, nuts, seeds, legumes, and whole grains. Most people obtain adequate amounts from a regular diet, but arginine can become conditionally essential in cases of certain metabolic disorders, prematurity, severe illness, or major trauma.

Medical use and supplementation vary. L-arginine is used in some contexts for urea cycle disorders and has been studied for cardiovascular disease and wound healing, but evidence for clear clinical benefits, especially for athletic performance, is mixed and not definitive. Supplements should be used under medical supervision when indicated.

Safety considerations include potential gastrointestinal upset at high doses and possible interactions with nitrates or other blood pressure–lowering medications. There is some concern about arginine's role in the replication of herpes simplex virus, so affected individuals may choose to avoid supplementation. Individuals with kidney disease or those who are pregnant should consult a clinician before use. Related compounds include L-citrulline, a metabolic precursor to arginine.