Citrulline is a non-essential amino acid, meaning that the body can manufacture it from other nutrients. Within the body, citrulline is converted to the amino acid L-arginine. Some of the proposed uses of citrulline supplements are based on raising levels of arginine. Citrulline also plays a role in a physiological process called “the urea cycle,” in which toxic ammonia is converted to urea.

The body manufactures citrulline from the essential amino acid glutamine. Deficiency of citrulline is unlikely to occur.