Conditionally Essential Amino Acid Nitric Oxide Precursor* Arginine is a conditionally essential basic amino acid involved primarily in urea metabolism and excretion, as well as in DNA synthesis and protein production.* It is an important precursor of nitric oxide (NO) and thus plays a role in the dilation of blood vessels.* This product has twice the L-Arginine (1,000 mg per tablet) as in our regular strength product (500 mg per capsule). The L-Arginine used in this product is pharmaceutical grade. Natural color variation may occur in this product.