NMN stands for nicotinamide mononucleotide, a molecule naturally occurring in all life forms. At the molecular level, it is a ribo-nucleotide, which is a basic structural unit of the nucleic acid RNA. Structurally, the molecule is composed of a nicotinamide group, a ribose and a phosphate group. NMN is the direct precursor of the essential molecule nicotinamide adenine dinucleotide (NAD+) and is considered a key component to increase NAD+ levels in cells.