Arginine and Citrulline are two amino acids that are integral to protein metabolism and utilization, as well as to the maintenance of muscle tissue. Both are key intermediates in the urea cycle, where they participate in the detoxification of ammonia via the production of urea. Arginine that has not been converted to urea, enters general circulation where it is distributed to various tissues and metabolized for other uses such as protein synthesis. Scientific studies have shown that supplementing Citrulline along with Arginine helps maintain nitrogen balance better than supplementation with Arginine alone. 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.FAMILY OWNED OPERATED: Our product is proudly packaged by a family owned and operated company since 1968. GMP Quality Assured: NPA A-rated GMP certification means that every aspect of the NOW manufacturing process has been examined, including our laboratory testing methods (for stability, potency, and product formulation). NITRIC OXIDE PRECUSOR PRE-WORKOUT SUPPLEMENT: Take one capsule up to twice a day, preferably before working out. PROTEIN METABOLISM : Arginine and citrulline are two amino acids that are integral to protein metabolism and utilization, as well as to the maintenance of muscle tissue . NOW Sports products are comprehensively tested so you can trust that our products are pure and effective for every level of athletics.