# NAD+: What the Randomized Human Trials Actually Measured > NAD+ is an endogenous redox coenzyme; its oral precursors NMN and NR raise whole-blood NAD+ dose-dependently in randomized trials. A cited, layered digest of the human evidence. A layered reading of the evidence: the coenzyme on the floor, the precursors (NMN, NR) stacked above, and the whole-blood NAD+ that the trials actually measured floated to the front. Every number cited. ## The short version NAD+ (nicotinamide adenine dinucleotide — a fuel-handling helper molecule that every cell uses to turn food into energy) is not a drug and not a single product you buy. It is a coenzyme (a helper molecule an enzyme needs to do its job) made inside your own cells, and its levels fall as the body ages. You cannot usefully swallow NAD+ itself — the molecule is too large and charged to absorb intact — so the studied oral route is to take a precursor (a building block the body converts into NAD+; NMN and NR are the common ones). In randomized trials, those precursors reliably raise the NAD+ measured in blood. This site summarizes what those published studies measured. It is not medical advice and sells nothing. ## What NAD+ is, in one stratum NAD+ is an endogenous redox coenzyme (redox is the electron-shuttling chemistry that releases energy from food) found in every living cell. It carries electrons through glycolysis, the TCA cycle and oxidative phosphorylation to make ATP, the cell's energy currency, and it is also consumed as a substrate by signaling enzymes — sirtuins, PARPs and CD38 — that govern DNA repair, gene regulation and inflammation [5]. Tissue NAD+ declines with age. One driver is CD38, an NAD+-consuming ectoenzyme that rises with age and inflammation; in mice, deleting CD38 preserved NAD+ and mitochondrial function into later life [2]. That decline is the rationale behind raising NAD+ with precursors. NAD+ is marketed as a dietary supplement, not an approved medicine. It is not FDA-approved to treat, prevent or reverse any disease. Most oral products are not NAD+ at all but its precursors — [nicotinamide mononucleotide research](/nicotinamide-mononucleotide) and [nicotinamide riboside trials](/nicotinamide-riboside) carry the bulk of the controlled human data. ## What the human trials measured The most replicated finding is pharmacodynamic: oral precursors raise the NAD+ measured in whole blood, dose-dependently. In healthy overweight adults, nicotinamide riboside (NR) at 100, 300 and 1000 mg/day for 8 weeks raised whole-blood NAD+ by 22%, 51% and 142% respectively, with no significant adverse-event difference from placebo and no flushing [4]. A separate randomized crossover found 1000 mg/day NR for 6 weeks raised whole-blood NAD+ by roughly 60% in middle-aged and older adults [7]. NMN shows the same dose-response. A multicenter, double-blind RCT gave 300, 600 or 900 mg/day for 60 days; blood NAD+ rose significantly at days 30 and 60 across all groups versus placebo (p ≤ 0.001), 600 mg/day was identified as the optimal dose, and walking distance improved [3]. Functional endpoints are more mixed. Ten weeks of NMN at 250 mg/day improved muscle insulin sensitivity in prediabetic, postmenopausal women, with no change in body composition or HbA1c [1]. The honest gap: raising blood NAD+ is demonstrated; translation to hard clinical endpoints in humans is not. A 2025 Nature Metabolism review concluded human efficacy data remain limited and tissue NAD+ data sparse [16]. The full set of [human clinical trials](/research) is laid out study by study. ## NAD+ itself vs its oral precursors Keeping this distinction straight is the whole point of the page. NAD+ is the destination molecule; NMN and NR are one or two biochemical steps upstream of it. Oral NAD+ is poorly absorbed intact, so a study of someone swallowing NMN or NR is not a study of "taking NAD+" — it is a study of a precursor that the body converts into NAD+ [6]. The practical consequence: nearly all the high-quality oral human data is precursor data. NR is converted to NMN by NRK kinases, then to NAD+; NMN sits one step from NAD+. Both reliably raise whole-blood NAD+ in randomized trials [4][3]. Plain oral "NAD+" capsules, by contrast, have little controlled support. The [NAD+ vs its precursors](/nicotinamide-mononucleotide) comparison is worked through in detail on the NMN page. Injectable and intravenous NAD+ exist as a separate, compounded wellness route with far thinner evidence — the [IV NAD+ pharmacokinetics](/research) and the oral [human clinical trials](/research) are both covered on the research page, never promoted here. ## What is NAD supplement used for? NAD+ is an endogenous coenzyme present in every cell; it is marketed as a dietary supplement, usually as the precursors NMN, NR or niacin, and studied for raising the blood NAD+ that declines with age. In trials, the measured endpoints are NAD+ elevation and metabolic or physical-function markers [4][1] — not approved disease treatments. This is a research summary, not a recommendation to use any product. ## What is an NAD injection? An NAD injection delivers NAD+ parenterally rather than orally; the intravenous form is a compounded wellness therapy that is not FDA-approved. A human pharmacokinetic pilot found infused NAD+ is extensively metabolized outside the cell and rapidly cleared from plasma [9]. Controlled efficacy evidence for the route is limited, and a compounded injectable NAD+ product has been subject to an FDA Class I endotoxin recall. ## Is NAD just vitamin B3? No. NAD+ is built from vitamin-B3-family precursors — nicotinamide, nicotinic acid and nicotinamide riboside — but it is itself a larger dinucleotide coenzyme, not a vitamin [5]. The B3 vitamers are the dietary inputs that feed NAD+ synthesis through the salvage and Preiss-Handler pathways; NAD+ is the molecule those inputs become. ## 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 — enzymes that govern DNA repair, gene regulation and inflammation [5]. In human skeletal muscle, low NAD+ biosynthesis tracks with reduced mitochondrial oxidative capacity and sarcopenia [13], underscoring its central metabolic role. ## Is NAD a peptide? No. NAD+ is a dinucleotide coenzyme — two nucleotides (nicotinamide mononucleotide and adenosine monophosphate) joined by two bridging phosphate groups — not a peptide or protein [5]. Its molecular formula is C21H27N7O14P2 and its molecular weight is 663.43 Da. ## What does NAD stand for? NAD stands for nicotinamide adenine dinucleotide. The "+" in NAD+ denotes the oxidized form — the electron acceptor — which becomes NADH when it is reduced by gaining electrons [5]. The two forms interconvert continuously as the cell makes and spends energy. ## What does NAD mean in medical terms? In biochemistry and medicine, NAD (nicotinamide adenine dinucleotide) is a coenzyme central to redox metabolism and a substrate for NAD+-consuming signaling enzymes such as sirtuins, PARPs and CD38 [5]. It is a normal cellular metabolite, not a prescription drug — present in every cell and synthesized continuously by the body. --- The NAD+ literature read in strata — the coenzyme at the base, its oral precursors above, and the blood-NAD+ the trials measured at the front — cited to source, with nothing here prescribed, dispensed, or sold.