NAD+ is a redox coenzyme, and most products on the label are its precursors, NMN and NR.

The short version

NAD+ (a fuel-handling helper molecule every cell uses to turn food into energy) is not a drug. It is an endogenous coenzyme (a helper molecule an enzyme needs to do its job) that your body already makes, and it is sold as a dietary supplement. The catch: NAD+ itself is large and poorly absorbed when swallowed, so most oral products are actually precursors (building blocks the body converts into NAD+ — NMN and NR are the common ones). In human trials, those precursors reliably raised the amount of NAD+ in blood. Whether that translates into living longer or preventing disease is, so far, unproven. This site summarizes the published studies and cites every number.

What the NAD+ literature has established

NAD+ (nicotinamide adenine dinucleotide) is the cell's central redox coenzyme. It shuttles electrons through glycolysis, the TCA cycle, and oxidative phosphorylation to make ATP, and it is also consumed as a substrate by signaling enzymes — sirtuins (a family of cellular-maintenance enzymes that cannot work without NAD+), PARPs (DNA-repair enzymes), and CD38 — that govern DNA repair, gene regulation, and inflammation ^[5]. Tissue NAD+ declines with age, partly because the NAD-consuming ectoenzyme CD38 rises; in mice, deleting CD38 preserves NAD+ levels and mitochondrial function with age ^[2].

That decline is the rationale behind NAD+ supplementation. Because the intact molecule is poorly taken up by cells, the approach that has the most human data is to supply NMN and NR precursors the body converts into NAD+. In a dose-ranging trial, oral NR raised whole-blood NAD+ by 22%, 51%, and 142% at 100, 300, and 1000 mg/day over 8 weeks, with no flushing ^[4]. A multicenter NMN trial found a dose-dependent blood-NAD+ rise at 300-900 mg/day over 60 days ^[3]. The blood-level effect is well demonstrated. The translation to hard clinical endpoints in humans remains preliminary — a 2025 Nature Metabolism review concluded the human efficacy data are still limited ^[10].

This digest organizes that record by route and by evidence tier: the human randomized-trial evidence on the NAD clinical trials page, the infusion data on the IV NAD research page, and how NAD+ works in the cell on the research page. More on the editorial approach is in about this research digest.

NAD as a Supplement: Why Most Oral Products Are Precursors

NAD+ itself is a large, charged dinucleotide (molecular weight 663.43 Da), and it is not freely taken up intact by most cells. That single pharmacology fact shapes the entire NAD supplement market: the products that actually raise measured NAD+ in human blood are not NAD+ capsules but its precursors — NMN (nicotinamide mononucleotide), NR (nicotinamide riboside), and the vitamin-B3 forms niacin and nicotinamide. The body converts these into NAD+ through the salvage pathway (recycling nicotinamide via the rate-limiting enzyme NAMPT), the NRK route (NR to NMN to NAD+), and the Preiss-Handler route (from nicotinic acid) ^[5].

The distinction matters for reading any label or study honestly. An oral-NMN or oral-NR trial is not a study of "taking NAD+" — it is a study of a precursor that the body builds NAD+ from. Across controlled trials, the precursors that moved whole-blood NAD+ the most were NR and NMN; in a 14-day randomized trial, both raised whole-blood NAD+ roughly 2-fold versus placebo, while nicotinamide (NAM) had no significant effect ^[13]. The supplement status of NMN is itself contested: the FDA has taken the position that NMN is excluded from the dietary-supplement definition because it was authorized for investigation as a drug — a marketplace dispute over labeling, not a finding that NMN is banned ^[10].

NAD+ vs Its Precursors (NMN, NR)

The common framing of NAD+ vs NMN gets the biology backwards: they are not rival products but a coenzyme and one of its building blocks. Oral "NAD+" capsules and NAD+ precursors are not interchangeable, and the difference is measurable. Plain NAD+ swallowed as a capsule is poorly absorbed intact, which is why most researchers consider the precursors the rational oral approach ^[10]. The precursors, by contrast, raise circulating NAD+ in a dose-dependent way: NR by up to 142% at 1000 mg/day over 8 weeks ^[4], and NMN dose-dependently across 300-900 mg/day over 60 days ^[3].

So when a product is marketed as "NAD+" but the studies behind it tested NMN or NR, the claim and the evidence are about different molecules. This site keeps that line sharp throughout: a precursor trial is reported as a precursor trial, and the readout the trials actually used — whole-blood NAD+ — is named as such. The deeper biochemistry of how NAD+ works in the cell and the full NAD+ safety and tolerability picture are covered on their own pages.

What 'NAD+ Precursor' Means

An NAD+ precursor is a building block the body enzymatically converts into NAD+. The two most-studied oral precursors are NMN and NR. NR is taken up and phosphorylated by the NRK1/NRK2 kinases to NMN, and NMN is then converted to NAD+ by NMNAT — a route that bypasses the rate-limiting NAMPT step of the classic salvage pathway ^[5]. Niacin (nicotinic acid) feeds NAD+ through the separate Preiss-Handler pathway. Calling these molecules "precursors" is not a marketing softener; it is the accurate biochemical description, and it is why an oral precursor can raise blood NAD+ ^[4] even though the intact NAD+ molecule is poorly absorbed.

What is NAD supplement used for?

NAD+ is an endogenous redox coenzyme; supplements (usually the precursors NMN, NR, or niacin) are studied for raising blood NAD+ levels. Cited trials measured outcomes such as muscle insulin sensitivity ^[1] and physical performance ^[3], not approved disease treatments. NAD supplements are not an FDA-approved therapy for any condition.

What does NAD do for the body?

NAD+ carries electrons through glycolysis, the TCA cycle, and oxidative phosphorylation to make ATP, and it is a consumed substrate for sirtuins, PARPs, and CD38 that govern DNA repair, gene regulation, and inflammation ^[5]. Tissue NAD+ declines with age ^[5]. It is a coenzyme your body makes, not a drug.

What does NAD stand for?

NAD stands for nicotinamide adenine dinucleotide — a dinucleotide of nicotinamide mononucleotide and adenosine monophosphate. It cycles between an oxidized form (NAD+) and a reduced form (NADH) ^[5]. Its molecular formula is C21H27N7O14P2 and its molecular weight is about 663.43 Da.