From the Manufacturer's Label:
Healthy Immune System function**
Citrulline is a non-essential amino acid that is an important intermediate in the urea cycle, functioning along with Arginine and Ornithine to rid the body of ammonia, a byproduct of protein metabolism.** Citrulline also plays an important role in the maintenance of a healthy immune system.**
Manufactured by Now Foods.Contains no sugar, salt, starch, yeast, wheat, gluten, corn, soy, milk, egg, shellfish or preservatives.