L-Arginine, also known simply as Arginine, is an amino acid that is used in the biosynthesis of proteins. It is known as a semi-essential amino acid and is commonly taken by bodybuilders. Arginine may help increase muscle mass and boost exercise endurance.* It may also support the heart, immune system, and skin.** These statements have not been evaluated by the Food and Drug Administration. This product is not intended to diagnose, treat, cure or prevent any disease.