L-Arginine Powder 1 lb, NOW FoodsL Arginine Powder L Arginine is a conditionally essential basic amino acid involved primarily in urea metabolism and excretion as well as DNA synthesis. What is the source of NOW L Arginine? L Arginine, like all NOW amino acids, is a synthetic substance produced in a laboratory. Because it is not derived from an animal source, it is considered a vegetarian product. Naturally occurring amino acids are typically derived from animal sources, but this