L-Arginine is a conditionally essential basic amino acid involved primarily in urea metabolism and excretion, as well as DNA synthesis. L-Arginine is the substrate for the synthesis of nitric oxide (NO), a cell-derived relaxing factor that is essential for regulating vascular tone and blood flow. It also supports the manufacture of creatine, an energy substrate for muscles. 95% of creatine is located in the skeletal muscle.  This is a double-strength formula. Our NOW natural and organic Supplements are an effective way to ensure you and your loved ones are getting essential vitamins, minerals and nutrients for daily optimal health. Since 1968, NOW has been making top quality products that are tested to the highest standards to empower people to lead healthier lives. Our promise - what is on the label, is precisely what is in the bottle.