Citrulline is a non-essential amino acid associated with the urea cycle, which removes toxic byproducts from protein digestion. Naturally found in watermelons, Citrulline is not used to build proteins like many other amino acids. Instead, it is converted by the kidneys into another amino acid, arginine, and a compound called nitric oxide. These are important for heart and blood vessel health, immunity, and other aspects of wellness. Citrulline is popular among athletes and bodybuilders as it can possibly improve blood flow, protein synthesis, and exercise performance while reducing fatigue and muscle soreness. Citrulline supplements, often in the form of citrulline malate, are widely used to boost sports performance and improve cardiovascular health, although more research is needed to understand its effectiveness fully.