RESEARCH DIGEST / NAD+ COENZYME · PRECURSORS
NAD+ is the cell's central redox coenzyme, and oral precursors reliably raise blood levels in human trials.
A specimen sheet of the NAD+ literature: which precursors raise whole-blood NAD+, by how much, and where the IV and human-outcome evidence stops. Every figure is stamped to a study.
The short version
NAD+ (a fuel-handling helper molecule every cell uses to turn food into energy) is not a drug and not a single product you buy. It is made inside your own cells, and tissue levels fall as you age. Because NAD+ itself is large and charged, swallowing it whole barely works — so most supplements use a precursor (a building block the body converts into NAD+; NMN and NR are the common ones). In randomized trials, oral NMN and NR reliably raised the NAD+ in people's blood. Whether that changes how anyone feels or ages is still an open question. This page reads the studies and stamps each number to its source.
What NAD+ is, in one paragraph
NAD+ (nicotinamide adenine dinucleotide) is a coenzyme (a helper molecule an enzyme needs to do its job) found in every living cell. It carries electrons through glycolysis, the TCA cycle, and oxidative phosphorylation to make ATP — the chemistry of releasing energy from food, called redox [5]. NAD+ is also a consumed substrate for three enzyme families: sirtuins (cellular-maintenance enzymes that cannot work without NAD+), PARPs (DNA-repair enzymes), and CD38 (an NAD-burning enzyme on cell surfaces) [5]. NAD+ is a small dinucleotide, formula C21H27N7O14P2, molecular weight 663.43 Da, CAS 53-84-9 — it is not a peptide and not a blend. Tissue NAD+ declines with age, and one driver is CD38 activity rising over time [2].
What is NAD+?
NAD+ is the cell's central redox coenzyme: a small molecule that accepts and donates electrons to drive energy metabolism, and that signaling enzymes consume to do DNA repair, gene regulation, and inflammation control [5]. The '+' marks the oxidized, electron-accepting form; the reduced form is NADH.
What does NAD stand for?
NAD stands for nicotinamide adenine dinucleotide. It is built from a nicotinamide ring and an adenine ring joined by two bridging phosphates. The '+' in NAD+ denotes the oxidized form that accepts electrons; NADH is the reduced form that donates them [5].
Is NAD+ a peptide?
No. NAD+ is a dinucleotide coenzyme, not a peptide. It is a small redox molecule made of two ring systems and two phosphates, with no amino acids and no peptide bonds [5].
What does NAD mean in medical terms?
In biochemistry, NAD (nicotinamide adenine dinucleotide) is a coenzyme central to cellular redox reactions and energy metabolism, and a substrate for the sirtuin, PARP, and CD38 enzyme families [5]. It is endogenous — your cells make it — and is marketed as a dietary supplement, not an approved drug.
What does NAD+ do for the body?
NAD+ shuttles electrons through glycolysis, the TCA cycle, and oxidative phosphorylation to make ATP, and it is the consumed substrate for sirtuins, PARPs, and CD38, which govern DNA repair, gene regulation, and inflammation [5]. When NAD+ falls, these enzymes have less to work with.
NAD+ as a supplement: why most oral products are precursors
Oral NAD+ taken as the intact molecule is poorly absorbed, so most products on the shelf are precursors — NMN (nicotinamide mononucleotide), NR (nicotinamide riboside), or niacin/nicotinamide [6][8]. These are smaller building blocks the body converts into NAD+ through distinct pathways. The two most-studied are NR, which enters the NAD+ pool through the NRK kinases, and NMN, which sits one biochemical step from NAD+ [6][9]. A NAD supplement, in practice, almost always means a precursor capsule or powder.
Keeping the distinction exact matters: a trial of oral NMN or NR is a trial of a precursor, not of NAD+ taken directly. The clearest demonstration is NR — a randomized study in healthy overweight adults raised whole-blood NAD+ by 22%, 51%, and 142% at 100, 300, and 1000 mg/day over eight weeks [4]. That is the precursor doing its job: feeding the NAD+ pool. The full breakdown sits on the NMN vs NR precursors page.
What the research has measured
The reproducible finding across randomized human trials is that oral precursors raise blood NAD+ in a dose-dependent way [4][3][7]. NR at 1000 mg/day for six weeks raised whole-blood NAD+ by about 60% in middle-aged and older adults, with no serious adverse events [7]. NMN at 300, 600, and 900 mg/day for 60 days raised blood NAD+ significantly at days 30 and 60 across all dose groups in a multicenter trial [3]. A single 1000 mg dose of NR raised NAD+ roughly 2.7-fold over 24 hours [6].
Functional endpoints are more mixed. Ten weeks of NMN at 250 mg/day improved muscle insulin sensitivity in prediabetic, postmenopausal women, without changing body composition or HbA1c [1]. The multicenter NMN trial reported improved walking distance [3]. But a 2025 Nature Metabolism review of the human evidence concluded that efficacy for hard clinical endpoints remains limited, and that data on tissue-specific NAD+ are sparse [15]. The honest summary: raising blood NAD+ is well demonstrated; translating that to how people feel or age is not yet settled. For the human clinical trials of NAD+ precursors, each result is stamped to its study.
When people search for NAD+ benefits, the responsible answer is to report only what was measured — a blood NAD+ rise, a muscle insulin-sensitivity change, a walking-distance change — and to flag where the literature stops, rather than to promise an outcome the trials did not test.
Where the evidence is thinnest
IV NAD+ research is the weakest part of the record. Infused NAD+ is rapidly cleared from plasma — a pilot study found near-complete removal within about the first two hours of infusion — and controlled efficacy data are limited, mostly pilot and retrospective [11]. IV/injectable NAD+ is a compounded wellness therapy, not an FDA-approved treatment, and a compounded injectable NAD+ product was subject to an FDA Class I recall for elevated bacterial endotoxin. Reported infusion symptoms include chest and abdominal discomfort, flushing, and nausea when run too fast. This site presents IV NAD+ strictly as an unapproved compounded therapy with documented quality and clearance findings, not as a treatment. See the doses used in NAD+ studies for the precursor and IV figures reported in the trials.