NAD+ (β-nicotinamide adenine dinucleotide; CAS 53-84-9) is an essential dinucleotide cofactor present in every living cell, where it functions as a central redox coenzyme in cellular metabolism and as a substrate for three families of NAD+-consuming enzymes: the sirtuins (SIRT1–7), the poly(ADP-ribose) polymerases (PARPs), and the cyclic-ADP-ribose synthases (CD38, CD157). Cellular NAD+ levels decline with advancing age in multiple tissues, and the rationale for “NAD+ boosting” interventions — whether by direct NAD+ administration or by precursor supplementation with nicotinamide riboside (NR) or nicotinamide mononucleotide (NMN) — derives from preclinical evidence that restoring NAD+ availability can support sirtuin-, PARP-, and metabolic-pathway function.
NAD+ pathway research has been the subject of multiple peer-reviewed human clinical trials, with the most rigorous published data involving the orally bioavailable NAD+ precursor nicotinamide riboside (NR) rather than direct NAD+ administration. In a 2018 randomized, double-blind, placebo-controlled crossover trial published by Martens and colleagues in Nature Communications, six weeks of oral NR at 1,000 mg/day was reported as well-tolerated and effectively stimulates NAD+ metabolism
in healthy middle-aged and older adults [3]. In a single published human pilot study of direct intravenous NAD+ administration (Grant et al., Frontiers in Aging Neuroscience, 2019), the investigators reported that no measurable changes in plasma NAD+ or its metabolites were detected during the first two hours of a 6-hour 750 mg intravenous infusion [1] — a pharmacokinetic finding with practical implications for any research protocol contemplating direct NAD+ administration.
NAD+ is not approved as a drug for any indication. Crystalline NR chloride (NIAGEN®) has received GRAS (Generally Recognized As Safe) status from the U.S. FDA for use in food products and has been the subject of two New Dietary Ingredient Notifications. Direct NAD+ is available in some jurisdictions as a research-use chemical and is also administered in some clinical and wellness settings, though the published peer-reviewed evidence base for direct NAD+ administration remains limited.
Important Note on the Evidence Base
Important note on the evidence base: The most rigorous published human randomized-controlled-trial data on the NAD+ pathway involves the orally bioavailable NAD+ precursors nicotinamide riboside (NR) and nicotinamide mononucleotide (NMN), rather than direct administration of NAD+ itself. Direct NAD+ has limited published human pharmacokinetic data and is not appreciably absorbed via the oral route. Published research on direct intravenous NAD+ administration is sparse. Three of the four studies cited on this page evaluate NAD+ precursors; one evaluates intravenous NAD+ directly. Each study identifies its compound and route of administration explicitly.
Mechanism of Action
NAD+ does not act on a single receptor target. Instead, the molecule participates in two distinct categories of cellular function: classical redox cofactor activity, and substrate-level signaling through three families of NAD+-consuming enzymes whose activity depends on cellular NAD+ availability.
Redox coenzyme function. NAD+ cycles between its oxidized form (NAD+) and reduced form (NADH) as it accepts and donates electrons during cellular respiration, glycolysis, the tricarboxylic acid cycle, and fatty acid β-oxidation. The phosphorylated forms (NADP+/NADPH) play complementary roles in biosynthetic reduction reactions, including fatty acid synthesis, cholesterol synthesis, and the regeneration of reduced glutathione. The cellular ratio of NAD+/NADH is a tightly regulated metabolic state variable; both excess reduction (high NADH, low NAD+) and oxidative stress affect this ratio in disease-relevant ways.
Sirtuin substrate. The sirtuin family (SIRT1–7) comprises NAD+-dependent deacetylases and deacylases that regulate transcription, DNA repair, mitochondrial biogenesis, and metabolic homeostasis. Sirtuin enzymatic activity is rate-limited by cellular NAD+ availability: when NAD+ levels fall, sirtuin activity falls in parallel. The hypothesis that age-related NAD+ decline contributes to age-related decline in sirtuin-dependent processes is a central organizing framework in the longevity-research literature.
PARP substrate. The poly(ADP-ribose) polymerases (PARPs) consume NAD+ during DNA damage repair, transferring ADP-ribose units from NAD+ to acceptor proteins. PARP activation in response to DNA damage can rapidly deplete cellular NAD+ pools, particularly under conditions of chronic genotoxic stress. This mechanism connects NAD+ pathway integrity to genomic stability.
CD38 / CD157 substrate. The cyclic-ADP-ribose synthases CD38 and CD157 consume NAD+ to generate cADP-ribose, a second messenger that regulates calcium signaling. CD38 expression increases with age in multiple tissues, and the increase in CD38-driven NAD+ consumption is one proposed mechanism for the age-related decline in cellular NAD+ levels.
Pharmacokinetic note — direct NAD+ vs. precursors. The pharmacokinetic literature distinguishes sharply between direct NAD+ administration and precursor administration. NAD+ itself is not appreciably absorbed via the oral route; direct NAD+ in research models is administered intravenously. The single published human IV NAD+ pharmacokinetic study (Grant 2019) reported that detectable plasma NAD+ metabolome changes appeared only after the 2-hour mark of a 6-hour infusion [1]. NAD+ precursors NR and NMN, by contrast, are orally bioavailable and produce concentration-dependent elevation of the blood NAD+ metabolome within hours of oral administration in healthy human volunteers [2][4].
Available Forms
Omnix Peptides supplies NAD+ in two research formats. Each lot is independently characterized by HPLC and LC–MS, with a batch-specific Certificate of Analysis available on each product page.
- NAD+ Vial — lyophilized powder for reconstitution. Available in 100 mg, 500 mg, and 1,000 mg strengths per vial. The vial is the research format used in the single published human IV NAD+ pharmacokinetic study (Grant 2019); it is also the canonical research format for protocols evaluating direct NAD+ exposure in cell-culture systems.
- NAD+ Liquid Spray — 1,500 mg per 30 mL bottle. Mucosal-administration format used in research models evaluating non-injectable delivery routes. Note that published human PK data on mucosal NAD+ administration is sparse; researchers evaluating this route should consult the primary pharmacokinetic literature.
NAD+ is classified under the Longevity & Anti-Aging research category. For research framed around overlapping mechanisms, see also the related compound hubs for Epithalon, Glutathione, MOTS-c, and 5-Amino-1MQ — all classified under the longevity research category in the Omnix catalog.
Amount in the Published Research Literature
The following administration ranges describe the protocols used in the peer-reviewed NAD+-pathway literature. They are reported here for research-reference purposes only and do not constitute administration recommendations of any kind. The literature is organized by route and compound, since the relevant pharmacokinetic profiles differ substantially.
Intravenous NAD+ (Grant 2019). The single published human pilot study of direct intravenous NAD+ administration enrolled 11 healthy male participants aged 30–55. The active arm (n = 8) received 750 mg of NAD+ in normal saline by intravenous infusion over 6 hours (approximately 2 mg/min, approximately 3 µmol/min); the saline-control arm (n = 3) received saline only [1]. Plasma and urine were collected throughout the infusion and follow-up period. As noted above, detectable plasma NAD+ metabolome changes appeared only after the 2-hour mark.
Oral nicotinamide riboside (NR) — Trammell 2016. The first formal human pharmacokinetic study of NR evaluated single oral amounts of 100 mg, 300 mg, and 1,000 mg in healthy adult volunteers, with serial blood and urine sampling over 24 hours [2]. The investigators reported that nicotinamide riboside is uniquely and orally bioavailable in mice and humans
, with all three amounts producing concentration-dependent increases in the blood NAD+ metabolome.
Chronic oral NR — Martens 2018. The 2 × 6-week randomized, double-blind, placebo-controlled crossover trial in 30 healthy middle-aged and older adults used 500 mg of NR twice daily (1,000 mg/day total) [3]. The investigators reported elevation of NAD+ in peripheral blood mononuclear cells and exploratory cardiovascular signals (reduction in systolic blood pressure and aortic pulse-wave velocity in subjects with above-normal baseline blood pressure), framed by the authors as hypothesis-generating findings requiring confirmation in larger trials.
Long-term oral NR — Conze 2019. The 8-week randomized, double-blind, placebo-controlled trial of crystalline NR chloride (NIAGEN®) in 140 healthy overweight men and women evaluated three amounts (100 mg/day, 300 mg/day, 1,000 mg/day) against placebo [4]. The investigators reported concentration-dependent increases in whole blood NAD+ of 22%, 51%, and 142% at the 100, 300, and 1,000 mg amounts respectively, with elevations achieved within 2 weeks and maintained through the 8-week treatment period. No significant differences in adverse events were observed between NR-treated and placebo-treated groups.
Researchers planning protocols are referred to the original primary literature cited in the References section for full methodological detail, including vehicle composition, infusion rate (for IV protocols), escalating-amount schedule, and biomarker selection.
Frequently Asked Questions
Is NAD+ FDA-approved?
NAD+ is not approved as a drug for any indication. The NAD+ precursor crystalline nicotinamide riboside chloride (NIAGEN®) has received GRAS (Generally Recognized As Safe) status from the U.S. FDA for use in food products and is the subject of two New Dietary Ingredient Notifications. Direct NAD+ and other NAD+ precursors (NMN, NR) are available in some jurisdictions as research-use chemicals and as dietary ingredients.
What is the difference between NAD+ and NAD+ precursors (NR, NMN)?
NAD+ is the active dinucleotide cofactor that participates in cellular metabolism and serves as a substrate for sirtuins, PARPs, and CD38. NAD+ precursors (nicotinamide riboside / NR; nicotinamide mononucleotide / NMN; nicotinamide / NAM; nicotinic acid / NA) are smaller molecules that the cell converts into NAD+ via salvage and de novo biosynthesis pathways. The most rigorous published human RCT data on the NAD+ pathway involves NR and NMN precursors, not direct NAD+. Direct NAD+ is not appreciably absorbed via the oral route; NR and NMN are orally bioavailable.
Has direct NAD+ been studied in humans?
Published peer-reviewed human research on direct NAD+ administration is sparse. The only published human pharmacokinetic study of intravenous NAD+ administration is Grant et al., Frontiers in Aging Neuroscience (2019), a pilot trial in 11 healthy male participants [1]. The investigators reported that no measurable changes in plasma NAD+ or its metabolites were detected during the first two hours of a 6-hour 750 mg intravenous infusion; detectable plasma NAD+ metabolome changes appeared only after the 2-hour mark.
What does Trammell 2016 show about oral NR bioavailability?
Trammell and colleagues conducted the first formal human pharmacokinetic study of nicotinamide riboside, evaluating single oral amounts of 100 mg, 300 mg, and 1,000 mg in healthy adult volunteers [2]. The investigators reported that nicotinamide riboside is uniquely and orally bioavailable in mice and humans
, with single oral amounts producing concentration-dependent increases in the blood NAD+ metabolome. They also identified nicotinic acid adenine dinucleotide (NAAD) as a sensitive biomarker of effective NAD+ repletion, a finding that has informed subsequent biomarker selection in NAD+-precursor trials.
What does Martens 2018 show about chronic NR in middle-aged adults?
Martens and colleagues at the University of Colorado Boulder conducted a 2 × 6-week randomized, double-blind, placebo-controlled crossover trial in 30 healthy middle-aged and older adults. Participants received 500 mg of NR twice daily (1,000 mg/day total) or matching placebo. The investigators reported that NR was well-tolerated and effectively stimulated NAD+ metabolism in peripheral blood mononuclear cells [3]. Exploratory analyses suggested NR may reduce systolic blood pressure and aortic pulse-wave velocity in subjects with above-normal baseline blood pressure; the authors framed these as hypothesis-generating findings requiring confirmation in larger trials.
What does Conze 2019 show about long-term NR safety?
Conze and colleagues conducted an 8-week randomized, double-blind, placebo-controlled trial of crystalline NR chloride (NIAGEN®) in 140 healthy overweight men and women, evaluating three amounts (100, 300, 1,000 mg/day) against placebo. NR consumption amount-dependently and significantly increased whole blood NAD+ by 22%, 51%, and 142% at the 100, 300, and 1,000 mg amounts respectively, with elevations achieved within 2 weeks and maintained through the 8-week treatment period [4]. No significant differences in adverse events were observed between NR-treated and placebo-treated groups.
What administration routes are described in the NAD+ research literature?
Direct NAD+ research in humans has used intravenous infusion (Grant 2019). NAD+ precursors NR and NMN have been studied via oral administration (Trammell 2016, Martens 2018, Conze 2019). Subcutaneous and intramuscular routes for direct NAD+ have been used in clinical and wellness settings but have limited published peer-reviewed pharmacokinetic data. Mucosal (intranasal, sublingual) routes for direct NAD+ are not well characterized in the peer-reviewed literature.
Why does cellular NAD+ decline with age?
The mechanisms underlying age-related NAD+ decline are multifactorial. Hypotheses supported in the published literature include increased NAD+ consumption by CD38 (whose expression rises with age in multiple tissues), reduced expression of nicotinamide phosphoribosyltransferase (NAMPT, the rate-limiting enzyme in the NAD+ salvage pathway), increased PARP activation due to accumulated DNA damage, and reduced precursor availability. The relative contribution of each mechanism varies by tissue and species.
References
- Grant R, Berg J, Mestayer R, et al. A pilot study investigating changes in the human plasma and urine NAD+ metabolome during a 6 hour intravenous infusion of NAD+. Front Aging Neurosci. 2019;11:257. doi:10.3389/fnagi.2019.00257 · PubMed: 31572171
- Trammell SAJ, Schmidt MS, Weidemann BJ, et al. Nicotinamide riboside is uniquely and orally bioavailable in mice and humans. Nat Commun. 2016;7:12948. doi:10.1038/ncomms12948 · PubMed: 27721479
- Martens CR, Denman BA, Mazzo MR, et al. Chronic nicotinamide riboside supplementation is well-tolerated and elevates NAD+ in healthy middle-aged and older adults. Nat Commun. 2018;9(1):1286. doi:10.1038/s41467-018-03421-7 · PubMed: 29599478
- Conze D, Brenner C, Kruger CL. Safety and metabolism of long-term administration of NIAGEN (nicotinamide riboside chloride) in a randomized, double-blind, placebo-controlled clinical trial of healthy overweight adults. Sci Rep. 2019;9(1):9772. doi:10.1038/s41598-019-46120-z · PubMed: 31278280
For Research Use Only. The products described on this page are sold strictly for in vitro laboratory research and are not intended for human or animal consumption, diagnostic use, or therapeutic use. The published research summarized above is provided as scientific reference material. Nothing on this page constitutes medical advice, a therapeutic claim, or a recommendation for any use outside of a properly resourced and ethically reviewed research setting.
