Arginine is a very popular amino acid supplement, usually used to promote better circulation and healthy blood pressure. Arginine can do this because it serves as the primary precursor to nitric oxide (NO), the body's vasodilator (relaxes and widens blood vessels to increase blood flow). Since arginine users usually take gram doses (2-5 grams), high potency 1 gram tablets like these made by NOW Foods are the best option. Arginine also has growth hormone promoting properties and may help increase protein synthesis in response to exercise or injury.