Citrulline is a type of α Amino acids, named after the watermelon that first extracted citrulline. Citrulline is generated from ornithine and aminoformyl phosphate in the urea cycle, or as a byproduct of arginine catalyzed by nitric oxide synthase (NOS). Firstly, arginine is oxidized to N-hydroxyarginine, which is then oxidized to citrulline and releases nitric oxide. Citrulline can relax human blood vessels, enhance male sexual function, and treat sexual dysfunction. Maintaining healthy lung function, improving mental clarity, and helping brain nerve cells store and retrieve information.。