Nicotinamide adenine dinucleotide (NAD+) is a coenzyme found in all living cells, essential for various metabolic processes. It is composed of two nucleotides joined through their phosphate groups, with one nucleotide containing an adenine base and the other nicotinamide. NAD+ is synthesized in the body from precursors such as tryptophan or niacin (vitamin B3), and it can also be derived from the diet. Researchers have extensively studied NAD+ for its role in cellular metabolism and its potential impact on aging and longevity. NAD+ is crucial in redox reactions, transferring electrons from one reaction to another, which is vital for energy production in cells. Studies have shown that NAD+ levels decline with age, and this reduction is associated with various age-related diseases. Researchers have investigated NAD+ for its potential to improve mitochondrial function, enhance DNA repair, and modulate immune responses. The mechanism of action of NAD+ involves its role as a substrate for several enzymes, including sirtuins, poly(ADP-ribose) polymerases (PARPs), and CD38, which are involved in cellular processes such as DNA repair, gene expression, and calcium signaling. By influencing these pathways, NAD+ helps maintain cellular health and function. Pharmacokinetic studies of NAD+ suggest that it has a relatively short half-life and is rapidly metabolized in the body. Its bioavailability varies depending on the route of administration, with oral bioavailability being notably low due to degradation in the gastrointestinal tract. Current research on NAD+ is focused on understanding its role in aging and developing therapeutic strategies to enhance its levels in the body. While NAD+ is not approved as a medicinal product, it is available as a dietary supplement in some regions. Regulatory agencies continue to evaluate its safety and efficacy for potential therapeutic use.