L-arginine

Also known as arginine, l arginine, arginine hcl.

Last reviewed October 9, 2026 · Jump to references

What is L-arginine?

In plain words

L-arginine is an amino acid, a building block of protein, that comes from food and is also made by the body. The body uses it to build proteins, remove waste nitrogen, and make nitric oxide, a substance that helps blood vessels relax. Researchers study it for blood flow, blood pressure, and exercise performance. Evidence for supplement benefits is mixed, and supplements can cause stomach upset and interact with medicines.

Technical definition

L-arginine is a proteinogenic α-amino acid with a guanidinium-containing side chain; it is synthesized in the body and is conditionally essential when physiological requirements exceed endogenous production. It serves as a substrate for nitric oxide synthases, which produce nitric oxide and L-citrulline, and for arginase in the urea cycle, supporting vascular signaling and nitrogen disposal. In the United States, it is sold as a dietary supplement, which does not require FDA approval for effectiveness before marketing.

Educational information only. This page does not provide medical advice or determine whether a supplement is appropriate for you. Review supplements with a qualified healthcare professional, especially if you take medication, are pregnant, have surgery scheduled, or have a chronic medical condition.

Evidence by use

Each use is rated on its own. There is no single overall effectiveness score.