L-Citrulline is a naturally occurring non-essential amino acid. Although L-Citrulline is not used in protein synthesis, it has several important functions with respect to amino acid and protein metabolism. L-Citrulline is involved in the formation of urea in the liver, and the synthesis and elimination of urea is essential for removing toxic protein metabolites from the body. In addition, L-Citrulline facilitates protein synthesis for muscle tissue retention and helps to maintain healthy protein balance.