What it is
NAD+ (nicotinamide adenine dinucleotide) is a coenzyme found in every living cell. It is essential to how cells turn food into energy and to dozens of repair and signalling processes. Strictly speaking NAD+ is not a peptide, but it is grouped with longevity compounds and frequently discussed alongside them. NAD+ levels in skin, blood, muscle and brain are thought to decline with age, which is the basis for "NAD+-boosting" strategies.
Most supplements do not contain NAD+ itself but a precursor the body converts into it, usually NMN (nicotinamide mononucleotide) or NR (nicotinamide riboside).
How it works
NAD+ acts as a shuttle for electrons in energy metabolism and as a required co-substrate for enzymes (such as sirtuins) involved in DNA repair, inflammation and cellular stress responses. The theory is straightforward: if NAD+ falls with age and underpins these processes, restoring it might support healthier aging.
What the evidence shows
Here the picture is nuanced, and worth getting right. Human trials consistently show one thing clearly, and are far less clear on another.
What is well supported: oral NR and NMN reliably raise NAD+ levels in the blood, and are generally well tolerated over weeks to months in studies. This "target engagement" is consistent across trials.
What is not well supported: translating that biochemical rise into measurable improvements in how people feel or function. Short-term trials in older adults have shown minimal or absent gains in cognition, vascular function and muscle performance. Some trials report specific benefits (for example reductions in cholesterol, body weight or blood pressure in particular sub-groups), but results are heterogeneous and often null. Reviewers consistently point to small sample sizes and short durations as limitations.
A note on IV NAD+
Intravenous NAD+ drips are offered by some wellness clinics. A 2026 systematic review found no eligible outcome trials testing IV or intramuscular NAD+ for anti-aging or wellness, meaning the popular IV route is the least supported by controlled evidence, not the most.
Where it stands
NR and NMN are widely sold as dietary supplements (their precise regulatory classification has shifted and varies by country). They are among the better-tolerated compounds in this library, but "well tolerated and raises a biomarker" is not the same as "proven to work." Treat strong benefit claims with caution.