L-Arginine and L-Citrulline are two amino acids bundled into a single powerful supplement. L-Arginine is an important factor in muscle metabolism and is a precursor for nitric oxide, which promotes increased circulation by relaxing blood vessels. L-Citrulline helps the body rid itself of ammonia, a by-product of exercise. This clearing enables the body to recover after a workout. L-Citrulline is an amino acid. It is turned into L-arginine in the kidneys after supplementation, which means L-citrulline supplementation is a more effective method of increasing L-arginine levels in the body than L-arginine supplementation. L-citrulline is an amino acid normally made by the body. In the body, L-citrulline is converted to L-arginine, another type of amino acid. L-arginine improves blood flow. It does so by creating nitric oxide (NO), a compound that helps widen blood vessels.