Amino SR Promotes Nitric Oxide Production Maintains Protein Balance Non-GMO A Dietary Supplement Vegetarian/Vegan GMP Quality Assured NOW L-Citrulline is a supplemental source of this non-essential but extremely important amino acid. Citrulline plays a unique role in the support of protein synthesis and positive nitrogen balance, particularly in muscle tissue, making it ideal for athletes and active individuals. NOW L-Citrulline Sustained Release (Amino SR) Tablets allow for prolonged citrulline release, which in turn supports sustained protein metabolism. This sustained release tablet is formulated for full release within 8 hours.