L-arginine is a protein amino acid present in the proteins of all life forms. It is classified as a semi-essential or conditionally essential amino acid. This means that under normal circumstances the body can synthesize sufficient L-arginine to meet physiological demands. There are, however, conditions where the body cannot.

L-arginine is essential for young children and for those with certain rare genetic disorders in which synthesis of the amino acid is impaired. Some stress conditions that put an increased demand on the body for the synthesis of L-arginine include trauma (including surgical trauma), sepsis and burns. Under these conditions, L-arginine becomes essential, and it is then very important to ensure adequate dietary intake of the amino acid to meet the increased physiological demands created by these situations.

L-arginine, even when it is not an essential amino acid as defined above, is a vital one. In addition to participating in protein synthesis, it plays a number of other roles in the body. These include the detoxification of ammonia formed during the nitrogen catabolism of amino acids via the formation of urea. In addition, L-arginine is a precursor in the formation of nitric oxide, creatine, polyamines, L-glutamate, L-proline, agmatin (a possible neurotransmitter in the brain) and the arginine-containing tetrapeptide tuftsin, believed to be an immunomodulator. It is a glycogenic amino acid; it can be converted to D-glucose and glycogen if needed by the body or it can be catabolized to produce biological energy.

L-arginine, when administered in high doses, stimulates pituitary release of growth hormone and prolactin and pancreatic release of glucagon and insulin. Intravenous L-arginine may be used as an aid in the evaluation of problems with growth and stature that may be due to growth hormone deficiency. Intravenous arginine hydrochloride may be used as a fourth-line agent in the treatment of severe metabolic alkalosis. It is also used as an immunonutrient in enteral and parenteral nutrition to help improve the immune status in those suffering from sepsis, burns and trauma.

Heart disease
In the body, L-arginine is used to make the compound nitric oxide, which reduces blood vessel stiffness, increases blood flow, and improves blood vessel function.

Erectile dysfunction
L-arginine has been used for erectile dysfunction. Like the drug Viagra, L-arginine enhances the action of nitric oxide, which relaxes muscles surrounding blood vessels supplying the penis. As a result, blood vessels in the penis dilate, increasing blood fow, which helps maintain erections. The difference in how they work is that Viagra blocks an enzyme called PDE5 that destroys nitric oxide and L-arginine is used to make nitric oxide.

In one study, 50 men with erectile dysfunction took either 5g of L-arginine per day or placebo. After 6 weeks, more men in the L-arginine group had an improvement compared to those taking the placebo. Unlike Viagra, L-arginine must be taken daily.

Wound healing
L-arginine's possible activity in wound repair may be due to its role in the formation of L-proline, an important amino acid that is essential for the synthesis of collagen.
L-arginine is predominately synthesized in the kidney. It is a key intermediate in the Krebs-Henseleit urea cycle. L-ornithine and L-citrulline are precursors in the synthesis of L-arginine, and L-arginine is converted to urea and L-ornithine via the enzyme arginase. The portion of L-arginine that is not converted to urea enters the circulation, and is distributed to the various tissues and metabolized as discussed above. A much smaller amount of L-arginine is produced in the liver.

L-Arginine is a semi-essential amino acid synthesized by the body from ornithine. It supports protein synthesis because it is involved in the transport and storage of nitrogen. L-Arginine is important for proper physical performance because it is used by the body to produce creatine. L-Arginine 1000 is from free base arginine, which is 17% more potent than arginine HCI (hydrochloride).