L-Citrulline is a naturally occurring amino acid that plays several roles in the body. It is one of the three amino acids in the urea cycle, alongside L-Arginine and L-Ornithine. In the kidneys, L-Citrulline is converted into arginine, which is a biological precursor of nitric oxide.

As a non-protein amino acid, L-Citrulline is rarely found in food, with the exception of watermelon. In fact, the name citrulline comes from watermelon’s Latin name, Citrullus vulgaris.