NAD+ is the coenzyme its precursors raise: what the trials actually measured.

The short version

NAD+ (a fuel-handling helper molecule every living cell uses to turn food into energy) is not a drug and not a single product you buy in a bottle. It is an endogenous coenzyme (a helper molecule an enzyme needs to do its job), sold as a dietary supplement. Most oral products are not NAD+ at all - they are precursors (building blocks the body converts into NAD+, chiefly NMN and NR), because the NAD+ molecule itself is large and poorly absorbed by mouth. This site reads the published NAD+ research and grades each finding by how far the evidence reaches: established human results, preclinical signals, and marketplace cautions kept clearly apart.

What the NAD+ literature establishes - and what it does not

NAD+ (nicotinamide adenine dinucleotide) is the cell's central redox carrier - it shuttles electrons through glycolysis, the citric-acid cycle and the mitochondrial electron-transport chain to make ATP, the cell's energy currency ^[5]. It is also a consumed substrate for a set of signaling enzymes that govern DNA repair, gene regulation and inflammation: the sirtuins, PARPs and CD38 ^[5]. Tissue NAD+ falls with age - in human skin and brain the decline is on the order of roughly 50% by middle-to-late life ^[6]. That decline is the rationale behind the whole NAD+ supplement category.

Here is the distinction the rest of this site protects. The most replicated human finding is narrow and real: oral precursors dose-dependently raise the NAD+ measurable in blood. In a randomized trial, nicotinamide riboside at 100, 300 and 1000 mg/day for eight weeks raised whole-blood NAD+ by 22%, 51% and 142% respectively, with no flushing and no adverse-event difference from placebo ^[4]. Oral NMN at 300-900 mg/day for 60 days raised blood NAD+ at every dose in a multicenter double-blind trial ^[3]. What the literature does not yet establish is the next link in the chain - that raising blood NAD+ translates into longevity, disease prevention or any hard clinical outcome. A 2025 Nature Metabolism review of the human evidence concluded exactly that: efficacy for hard endpoints remains limited and tissue-level NAD+ data are sparse ^[16].

NAD+ as a dietary supplement: what the research shows

NAD+ and its precursors are sold as dietary supplements, not approved drugs - NAD+ is not FDA-approved for any disease ^[16]. Because intact NAD+ is large and charged and is not freely taken up by most cells, the rational oral approach in the research is a precursor: nicotinamide riboside (NR), nicotinamide mononucleotide (NMN), or plain niacin/nicotinamide. These are converted to NAD+ inside the body through the salvage and Preiss-Handler routes ^[13].

Two caveats belong on this page in plain sight. First, the regulatory status of NMN is 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 that creates uncertainty for sellers, not a finding that NMN is "banned" or illegal ^[16]. Second, supplement-grade purity and actual content vary between products, and third-party testing is not guaranteed. None of that changes the underlying biochemistry; it changes what a buyer can verify. For the precursor distinction in detail, see NMN vs NR; for the doses actually studied, see doses used in the research.

What the studies measured: NAD+ in research

The honest summary of NAD+ benefits in the human literature is a short list of measured outcomes, not a wellness promise. Ten weeks of oral NMN at 250 mg/day improved muscle insulin sensitivity in prediabetic, postmenopausal women, with no change in body composition or HbA1c ^[1]. In the 60-day multicenter NMN trial, blood NAD+ rose at all doses and self-reported walking distance and quality-of-life scores improved versus placebo, with 600 mg/day identified as the optimal dose and no safety signal at any dose ^[3]. The mechanistic backbone is well established across model organisms: sirtuins (a family of cellular-maintenance enzymes that cannot work without NAD+) are rate-limited by how much NAD+ is available ^[7], and the NAD-consuming enzyme CD38 rises with age to drive the tissue NAD+ decline ^[2]. The throughline of this site is that these established results sit on one tier and the marketed claims sit on another - read the full NAD+ research findings for how each is graded.

Three routes, three very different evidence bases

The market sells NAD+ three ways, and the controlled evidence behind them is wildly uneven. Oral precursors (NMN, NR capsules and powders) carry the bulk of the human data and are the only route with multiple randomized trials ^[3][4]. Plain oral "NAD+" capsules are the weakest oral option - the intact molecule is poorly absorbed, which is why precursors exist. IV and injectable NAD+ is a compounded wellness therapy with the thinnest controlled evidence; infused NAD+ is rapidly cleared from plasma, and a compounded injectable NAD+ product was subject to an FDA Class I recall for endotoxin contamination ^[16]. Those are not equivalent products with a price difference - they are three different evidence tiers, which is the whole point of NAD injection and IV NAD+ as its own page. The mechanism behind it all - NAD+ as a substrate for sirtuins, PARPs and CD38 - is detailed on the research page.

What is NAD supplement used for?

NAD+ is an endogenous redox coenzyme central to energy metabolism. In research it is studied as a dietary supplement - usually via precursors (NMN, NR) that raise blood NAD+ - against age-related declines in NAD+ ^[5][6]. It is not an approved treatment for any disease, and trials measure markers like blood NAD+ and insulin sensitivity, not cures ^[16][1].

What does NAD do for the body?

NAD+ shuttles electrons through glycolysis, the citric-acid cycle and oxidative phosphorylation to make ATP, the cell's energy currency ^[5]. It is also a consumed substrate for signaling enzymes - sirtuins, PARPs and CD38 - that govern DNA repair, gene regulation and inflammation ^[5]. Both roles draw on the same intracellular NAD+ pool ^[9].

What does NAD stand for?

NAD+ stands for nicotinamide adenine dinucleotide. The "+" denotes the oxidized form; the reduced form is written NADH ^[5]. It is also historically called Coenzyme I. The name describes the structure: a nicotinamide unit and an adenine unit, each part of a nucleotide, joined into a dinucleotide ^[5].

Is NAD just vitamin B3?

No. NAD+ is built from vitamin B3 forms - niacin (nicotinic acid), nicotinamide and nicotinamide riboside all feed into it - but NAD+ itself is a distinct dinucleotide coenzyme, not a vitamin ^[5][13]. It is related to B3 as a downstream product, not identical to it; the precursors are the B3-family pieces the body assembles into NAD+.

Is NAD a peptide?

No. NAD+ is a dinucleotide redox coenzyme - two nucleotides joined by a two-phosphate bridge - not a peptide and not a blend ^[5]. Peptides are short chains of amino acids; NAD+ is a different class of molecule entirely, an endogenous coenzyme the body synthesizes from tryptophan, niacin and recycled nicotinamide ^[5][13].

What does NAD mean in medical terms?

In medical and biochemical terms, NAD+ is the coenzyme nicotinamide adenine dinucleotide, historically Coenzyme I - central to redox metabolism and to NAD-consuming signaling through sirtuins, PARPs and CD38 ^[5]. Its molecular weight is 663.43 Da and its CAS number is 53-84-9 ^[5]. It is a normal cellular metabolite, not a drug.