Nicotinamide adenine dinucleotide (NAD+)
NAD, NAD+, beta-NAD, coenzyme I, diphosphopyridine nucleotide, DPN
NAD+ is not a peptide. It is a dinucleotide coenzyme, built from nicotinamide and adenine linked through two ribose sugars and a pyrophosphate bridge, and it is present in every living cell. It is included in this library because it is sold and discussed alongside longevity peptides, not because it belongs to the same chemical class. Tissue NAD+ falls with age, and precursor supplements reliably raise blood NAD+; whether that translates into any functional benefit remains unresolved.
Mechanism
NAD+ has two separable roles. As a redox cofactor it cycles between NAD+ and NADH, carrying electrons through glycolysis, the tricarboxylic acid cycle and oxidative phosphorylation. In this capacity it is recycled rather than consumed, and the cell holds a modest pool.
The role that drives longevity interest is different. NAD+ is a consumed substrate for three families of enzymes that cleave it and release nicotinamide: the sirtuins (SIRT1 to SIRT7), which are NAD+-dependent deacylases regulating mitochondrial biogenesis, DNA repair and metabolic gene expression; PARP1 and PARP2, which consume NAD+ heavily during DNA damage repair; and the ectoenzyme CD38, an NAD+ glycohydrolase whose expression rises markedly with age and inflammation. Because these enzymes consume NAD+, the pool must be continually replenished, chiefly through the salvage pathway in which nicotinamide is converted by NAMPT to nicotinamide mononucleotide (NMN) and then by NMNAT enzymes to NAD+.
The ageing hypothesis follows: NAD+ declines with age, partly through increased CD38-mediated degradation and partly through reduced salvage capacity, and this decline starves sirtuins of substrate, impairing mitochondrial function and DNA repair. Supplying precursors, principally nicotinamide riboside (NR) or NMN, is proposed to restore the pool. Note that oral NAD+ itself is poorly absorbed intact and is largely broken down in the gut, which is why the trials use precursors rather than NAD+.
What the research shows
The pharmacological question is settled: oral NR and NMN raise blood NAD+ in humans, dose-dependently and reproducibly. Martens and colleagues showed 1000 mg/day NR for six weeks roughly doubled NAD+ in peripheral blood mononuclear cells in healthy middle-aged and older adults, with good tolerability. Elhassan and colleagues showed 1000 mg/day NR for 21 days augmented the aged human skeletal muscle NAD+ metabolome and produced anti-inflammatory transcriptomic signatures, but without improving muscle mitochondrial bioenergetics.
The clinical question is not settled. In the same Martens trial, the co-primary cardiovascular endpoints were not met, with only a suggestion of reduced systolic blood pressure in a hypertensive subgroup. Dollerup and colleagues gave 2000 mg/day NR to obese insulin-resistant men for 12 weeks and found no improvement in insulin sensitivity, no change in body composition, and no change in resting energy expenditure. That is a well-conducted negative result at a high dose. Yoshino and colleagues found that 250 mg/day NMN for 10 weeks increased muscle insulin sensitivity in prediabetic postmenopausal women, though without changes in body composition, blood pressure or most metabolic markers, and the finding attracted published methodological debate.
Meta-analyses reflect this pattern. Pooled analyses of NAD+ precursors have found no consistent effect on blood pressure, C-reactive protein or carotid intima-media thickness, and pooled analyses of muscle mass and function have found effects that are limited at best. The fair summary is that these compounds do what they say on the tin biochemically and have not yet demonstrated a clinically meaningful outcome in any well-powered trial. Intravenous NAD+, sold at high prices through clinics, has essentially no controlled efficacy evidence at all, and there is no published trial showing that intravenous administration achieves anything oral precursors do not.
Evidence assessment
Mixed evidence
Multiple randomised placebo-controlled human trials exist and consistently show NAD+ elevation, but functional and clinical outcomes are small, conflicting or null, and trials are short.
Tiers are applied consistently across the library and re-checked when new trials read out. Read the grading method.
Key studies
Chronic nicotinamide riboside supplementation is well-tolerated and elevates NAD+ in healthy middle-aged and older adults Mixed evidence
NR roughly doubled NAD+ in peripheral blood mononuclear cells and was well tolerated, but did not meet cardiovascular co-primary endpoints; a reduction in systolic blood pressure was suggested only in a hypertensive subgroup.
A randomized placebo-controlled clinical trial of nicotinamide riboside in obese men: safety, insulin-sensitivity, and lipid-mobilizing effects High-quality evidence
NR was safe but did not improve insulin sensitivity, body composition or resting energy expenditure in obese insulin-resistant men.
Nicotinamide Riboside Augments the Aged Human Skeletal Muscle NAD+ Metabolome and Induces Transcriptomic and Anti-inflammatory Signatures Mixed evidence
NR raised the skeletal muscle NAD+ metabolome and produced anti-inflammatory transcriptomic and circulating cytokine changes, without improving muscle mitochondrial bioenergetics.
Nicotinamide mononucleotide increases muscle insulin sensitivity in prediabetic women Mixed evidence
NMN increased skeletal muscle insulin sensitivity as measured by clamp, without changes in body composition, blood pressure or most metabolic markers.
The Effect of Nicotinamide Mononucleotide and Riboside on Skeletal Muscle Mass and Function: A Systematic Review and Meta-Analysis High-quality evidence
Pooled data showed limited effect of NMN or NR supplementation on skeletal muscle mass and function.
Effects of NAD+ precursors on blood pressure, C-reactive protein concentration and carotid intima-media thickness: A meta-analysis of randomized controlled trials High-quality evidence
NAD+ precursor supplementation did not produce consistent improvements in blood pressure, C-reactive protein or carotid intima-media thickness.
Safety
Oral NR at 1000 to 2000 mg/day and NMN at 250 to 1250 mg/day have been well tolerated in trials lasting up to 12 weeks, with adverse events comparable to placebo. The limits are duration and population: no trial has run long enough to characterise multi-year use, and participants have generally been healthy or metabolically at-risk adults rather than people with cancer or serious illness. One theoretical concern that recurs in the literature is that tumour cells have high NAD+ demand and some depend on the salvage pathway, so raising systemic NAD+ availability in the presence of an occult malignancy has an uncertain effect. This has not been demonstrated as a clinical harm, but it has also not been excluded. Intravenous NAD+ carries the additional and unnecessary risks of any infusion, and infusion-related discomfort is commonly reported.
Regulatory status
| Jurisdiction | Status |
|---|---|
| United Kingdom | NAD+ precursors are regulated as food supplements rather than medicines, subject to novel food rules; NMN's novel food status in Great Britain has been contested and differs from that in the EU. Intravenous NAD+ has no marketing authorisation and no approved indication. |
| United States | Nicotinamide riboside has an accepted new dietary ingredient notification and FDA 'no questions' GRAS status (GRN 000635) for use in foods and beverages. NMN was excluded from the dietary supplement definition by the FDA in 2022 on drug-exclusion grounds; following a citizen petition and litigation the FDA reversed that position, concluding in September 2025 that NMN is not excluded, and issued letters confirming NMN may be lawfully marketed as a dietary supplement. NAD+ itself is not an approved drug for any indication, and intravenous NAD+ administered in clinics is not FDA-approved. |
| WADA (sport) | NAD+ and its precursors are not on the WADA Prohibited List. As endogenous metabolites and permitted dietary supplements they fall outside the prohibited classes, though athletes remain responsible for supplement contamination. |
Questions
No. NAD+ is a dinucleotide coenzyme made of nicotinamide and adenine joined through two ribose sugars and a pyrophosphate bridge. It contains no amino acids and no peptide bonds. It appears in peptide libraries only because it is sold and marketed alongside them.
They reliably raise blood NAD+ levels, which is a real and reproducible pharmacological effect. Whether that produces any clinical benefit is unresolved: the largest well-dosed trials found no improvement in insulin sensitivity, body composition or cardiovascular measures, and meta-analyses of muscle and cardiometabolic outcomes have been largely null.
There is no controlled evidence that it is. No published trial has shown that intravenous NAD+ achieves a clinical outcome that oral nicotinamide riboside or NMN do not, and the infusion route adds cost, discomfort and procedural risk without demonstrated benefit.
NR (nicotinamide riboside) and NMN (nicotinamide mononucleotide) are precursors in the salvage pathway that the body converts into NAD+. Oral NAD+ itself is largely degraded in the gut, which is why essentially all human trials use the precursors instead.