NOW® L-Arginine comes in 500 mg capsules and is non-GMO. 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.* The L-Arginine used in this product is pharmaceutical grade. Natural color variation may occur in this product.