NAD+ is the cell's central coenzyme, and the precursor trials are where its numbers actually live.

The short version

NAD+ (nicotinamide adenine dinucleotide, a fuel-handling helper molecule every cell uses to turn food into energy) is not a drug and not a single product on a shelf. It is a coenzyme (a helper molecule an enzyme needs to do its job), and the body makes it from precursors (building blocks the body converts into NAD+ — NMN and NR are the common ones). Tissue NAD+ falls as we age. Plain NAD+ swallowed as a pill is poorly absorbed; the trials that actually raised blood NAD+ in people used the precursors. This page files what those studies measured, and keeps the coenzyme separate from the building blocks.

What the NAD+ record actually shows

NAD+ sits at the center of cellular energy. It carries electrons through glycolysis, the citric-acid cycle, and the mitochondrial electron-transport chain to make ATP, and it doubles as a consumed fuel for signaling enzymes — the sirtuins, the PARPs, and CD38 — that govern DNA repair, gene regulation, and inflammation ^[5]. Tissue levels of this coenzyme decline with age, and that decline is the entire rationale behind the supplement category ^[5].

Here is the distinction this digest holds firm, because most coverage blurs it: NAD+ the molecule is large and charged (molecular weight roughly 663 Da), and it is poorly taken up intact when swallowed. The compounds people actually take are precursors — nicotinamide mononucleotide (NMN), nicotinamide riboside (NR), and the older vitamin-B3 forms niacin and nicotinamide — which the body converts into NAD+ through the salvage and Preiss-Handler pathways ^[9]. When a study reports that participants "took NAD+," check the methods: almost always they took a precursor. We never conflate the two.

The human evidence for raising blood NAD+ is genuinely strong. In a multicenter, double-blind, placebo-controlled trial, oral NMN at 300, 600, and 900 mg/day for 60 days raised blood NAD+ dose-dependently in middle-aged adults, with the increase significant at days 30 and 60 across every NMN group (p≤0.001) ^[3]. Oral NR ran a cleaner dose-response still: 100, 300, and 1000 mg/day for eight weeks lifted whole-blood NAD+ by 22%, 51%, and 142% respectively, with no flushing and no significant adverse-event difference from placebo ^[4]. Those are the headline figures, and they replicate. Browse the human clinical trials for the full register, or the NMN vs NR comparison for the precursor-by-precursor read.

NAD+ as a dietary supplement: what the label means

An NAD supplement is a dietary supplement, not an approved medicine — NAD+ and its precursors are not FDA-approved to treat, prevent, or cure any disease ^[8]. What the bottle delivers is, in nearly every case, a precursor that the body builds into NAD+, not the coenzyme itself in a usable oral form. That is the most important thing the label does not tell you, and it is why a reader chasing results should read "NAD supplement" as "NAD precursor supplement."

Two regulatory wrinkles belong in plain view. First, the supplement 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, which has created marketplace uncertainty rather than a settled ban ^[8]. Second, injectable and IV NAD+ — sold in wellness settings — is a compounded preparation, not an approved product, and a compounded NAD+ injection has been subject to an FDA Class I recall over elevated bacterial endotoxin ^[8]. Both points are filed under the caution desk on the research page, not buried.

How this digest is organized

We file by department, the way a newspaper files by desk. NMN — the highest-volume precursor — gets its own page, drawing on the NMN research and the human trials that used it. NR, the most clinically studied precursor, runs head-to-head with NMN on the NMN vs NR comparison page. The doses studied in the literature are catalogued as study parameters, never as instructions. And the common questions about NAD+ collect the definitional and safety questions readers actually ask.

Every quantitative claim on this site carries a citation to a named study, and the full reference list resolves each one to its PubMed record. This is editorial work — a reading of the published science. It is not medical advice, and nothing here is for sale.

What is NAD supplement used for?

NAD+ is an endogenous redox coenzyme; supplements — mostly the precursors NMN, NR, or niacin — are studied for raising the blood NAD+ levels that decline with age ^[5][9]. In trials, those precursors reliably increase blood NAD+, but this is research framing: NAD+ is not an approved treatment for any condition, and no dosing instruction is given here.

Is NAD just vitamin B3?

No. NAD+ is the coenzyme itself; vitamin B3 forms — niacin, nicotinamide, and the precursors NR and NMN — are the building blocks the body converts into NAD+ via the salvage and Preiss-Handler pathways ^[9]. The vitamins are upstream of the coenzyme, not the same molecule, which is exactly the distinction this digest keeps firm.

What does NAD do for the body?

NAD+ carries electrons through energy metabolism — glycolysis, the citric-acid cycle, and oxidative phosphorylation — to make ATP, and it is a consumed substrate for the sirtuins, PARPs, and CD38, the enzymes governing DNA repair, gene regulation, and inflammation ^[5]. It is the cell's central redox currency and a signaling fuel at once.

Is NAD a peptide?

No. NAD+ is a dinucleotide coenzyme — nicotinamide joined to adenine through two bridging phosphates — not a peptide and not a protein. It is a small endogenous metabolite of roughly 663 Da, with the molecular formula C21H27N7O14P2 ^[5]. The "prescribed" in this site's name is editorial framing for a research desk, not a claim that NAD+ is a peptide or a drug.

What does NAD stand for?

NAD stands for nicotinamide adenine dinucleotide. The plus sign in NAD+ denotes the oxidized form, which is reduced to NADH when the cell breaks down fuel; NADH then hands its electrons to the electron-transport chain to drive ATP synthesis ^[5]. The pair cycles continuously — the redox couple at the heart of metabolism.

What does NAD mean in medical terms?

In biochemistry, NAD refers to nicotinamide adenine dinucleotide, the central redox coenzyme historically called Coenzyme I ^[5]. It is an endogenous metabolite present in every living cell — not a prescription drug, not a single marketed medicine, and not on any approved-indication label. This site reads the research record on it, nothing more.