L- Arginine HCL is a synthetically manufactured form of arginine that combines the amino acid with a hydrogen chloride molecule. Hydrogen chloride is combined with arginine to make the supplement more palatable and to enhance its absorption by the digestive system. It causes vasodilation, or an increase in the diameter of blood vessels. Present in a vary range of products like fortified food supplement or in dietary supplements in capsule, tablet or powder form, commonly used by athletes to increase oxygen delivery and blood flow during exercise.