Dietary Supplement Convert Fat Into Energy Purity & Potency Guaranteed NAC (N-Acetyl-L-Cysteine) is a highly stable form of cysteine that provides antioxidant support and is especially beneficial for active people, the elderly and those exposed to polluted environments. Natural Factors amino acids are the highest quality pharmaceutical grade products available. Manufactured by Natural Factors to ensure safety and potency in accordance with the Good Manufacturing Practices (GMP), of the FDA and Health Canada.