GNC L-Arginine and L-Citrulline: Help Maintain Blood Vessel Tone GNC L-Arginine and L-Citrulline is an amino acid dietary supplement that can fuel nitric oxide production. Nitric oxide is essential for many aspects of your health—perhaps one of its most important functions is improving vasodilation for your blood vessels, which allows oxygen and nutrients to travel throughout your body. L-Arginine supplement helps maintain blood vessel tone L-Arginine and L-Citrulline supplements help to increase nitric oxide production Take one to three caplets of this supplement daily These statements have not been evaluated by the Food & Drug Administration. This product is not intended to diagnose, treat, cure, or prevent any disease.