L-arginine is a conditionally essential amino acid. It functions in the body as a natural precursor for the synthesis of nitric monoxide (NO). It also plays a physiological role in vascular function. Numerous studies have shown that nitric oxide dilates blood vessels and lowers blood pressure. Arginine deficiency can lead to circulatory problems, high blood pressure, and erectile dysfunction. As a conditionally essential amino acid, L-arginine can be produced by the body itself, but not always in sufficient quantities.