Nicotinamide adenine dinucleotide (NAD) free acid is widely used in biochemical research as a coenzyme in redox reactions, playing a critical role in energy metabolism. It is essential for studying cellular respiration, glycolysis, and the citric acid cycle. In enzymatic assays, NAD free acid serves as a substrate or cofactor to measure the activity of dehydrogenases and other enzymes. It is also utilized in metabolic pathway analysis to understand cellular energy dynamics and oxidative stress. Additionally, NAD free acid is employed in the development of therapeutic strategies targeting age-related diseases, as it is involved in sirtuin activation and DNA repair processes. Its role in NAD+ supplementation research is significant for exploring treatments for neurodegenerative disorders and metabolic syndromes.