NAD+ is the coenzyme every cell runs on, and the precursor trials that raise it.

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 on a shelf. It is a coenzyme (a helper molecule an enzyme needs to do its job) the body makes in every cell, and its levels in tissue fall as we age. Most oral products labeled for NAD+ are actually precursors (building blocks the body converts into NAD+ — NMN and NR are the common ones), because NAD+ itself is large and barely absorbed whole. The clear finding from controlled trials: those precursors raise the NAD+ in your blood. The harder, unsettled question is what that change does for health in people.

What the NAD+ literature has actually established

NAD+ — nicotinamide adenine dinucleotide — is the cell's central redox carrier (redox is the chemistry that shuttles electrons to release energy). It accepts and donates electrons through glycolysis, the TCA cycle, and the mitochondrial electron transport chain to drive ATP synthesis ^[5]. It is also a consumed substrate for three families of signaling enzymes — sirtuins (cellular-maintenance enzymes that cannot work without NAD+), PARPs (DNA-repair enzymes), and CD38 (an enzyme that rises with age and inflammation) — which together govern DNA repair, gene regulation, and metabolism ^[5].

Tissue NAD+ declines with age, and one mechanism is well mapped: CD38, the principal NAD+-consuming ectoenzyme, climbs with age and drives the fall. CD38-knockout mice are protected against age-related NAD+ decline and retain better mitochondrial function and metabolic health ^[2]. That decline is the rationale for trying to boost NAD+ — and because the molecule itself is poorly absorbed intact, boosting is done with precursors.

In humans, the precursor trials are consistent on one endpoint. Nicotinamide riboside (NR) raised whole-blood NAD+ by 22%, 51%, and 142% at 100, 300, and 1000 mg/day over eight weeks in healthy overweight adults — a clean dose-response with no flushing and no adverse-event difference from placebo ^[4]. A multicenter trial of NMN (300-900 mg/day for 60 days) raised blood NAD+ at every dose versus placebo and improved walking distance ^[3]. The 2025 Nature Metabolism review is the honest counterweight: raising blood NAD+ is reproducible, but translation to hard clinical endpoints in people remains preliminary, and tissue-level NAD+ data stay sparse ^[10].

NAD+ as a Dietary Supplement: What the Trials Measured

NAD+ is regulated as a dietary supplement, not as an approved medicine for any disease. When you see a NAD supplement on a label, what is usually inside is a precursor — NMN (nicotinamide mononucleotide), NR (nicotinamide riboside), or plain niacin/nicotinamide — not NAD+ itself, because the intact dinucleotide is large, charged, and poorly taken up by cells whole ^[10].

What the controlled human trials measured, repeatedly, is whole-blood NAD+ — the most common pharmacodynamic readout because sampling tissue NAD+ in people is invasive and rare. On that endpoint the supplements work: oral NR and NMN raise blood NAD+ dose-dependently ^[4][3]. On functional endpoints the picture is mixed. One trial reported improved muscle insulin sensitivity after 250 mg/day NMN ^[1]; a 2025 meta-analysis of 12 NMN randomized trials (513 participants) found no significant change in fasting glucose, triglycerides, or cholesterol versus placebo, and flagged variable study quality ^[14].

The regulatory picture has one live dispute. 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 controversy over NMN's supplement status, not a finding that NMN is unsafe or banned ^[10]. The most-replicated NMN research dose is 250 mg/day; see the doses used in NAD+ studies.

Injectable and IV NAD+: A Compounded Wellness Therapy

A NAD injection or intravenous infusion delivers NAD+ parenterally in wellness and clinical settings, bypassing the absorption problem of oral NAD+. It is also the route with the weakest controlled evidence of any in this literature, and it carries documented quality risks ^[10].

Infused NAD+ is cleared from plasma fast. A pharmacokinetic pilot found plasma NAD+ near-undetectable for roughly the first two hours of a six-hour infusion before rising, with extensive extracellular metabolism along the way ^[10]. Reported infusions run slowly — over roughly 1.5 to 6 hours — because faster rates provoke chest tightness, abdominal discomfort, flushing, and nausea ^[10]. These products are typically compounded, not FDA-approved, and a compounded injectable NAD+ product was subject to an FDA Class I recall for elevated bacterial endotoxin ^[10]. We frame IV NAD+ as an unapproved compounded therapy with real quality risks and the thinnest evidence base, never as an approved treatment. Read more on IV NAD+ tolerability.

Why oral products are precursors, not NAD+ itself

A short note on scope, because it governs how to read every study on this site. NAD+ itself is a large dinucleotide coenzyme (molecular weight 663.43 Da); most cells do not take it up intact, so swallowing 'NAD+' is not an efficient way to raise cellular NAD+ ^[10]. The rational oral approach is a NAD+ precursor — a smaller molecule the body's salvage pathway converts into NAD+. NR is phosphorylated by NRK kinases to NMN, then to NAD+ ^[7]; NMN sits one biochemical step from NAD+ via the enzyme NMNAT ^[8]. So when a trial reports that 'NAD+ went up,' check what was actually given: in nearly every well-controlled study it was oral NR or NMN, not NAD+. We keep that distinction exact throughout — an oral-NMN or oral-NR study is never described here as 'taking NAD+.' Which of the two precursors raises NAD+ more is its own question, taken up in NMN vs NR, and the age-related fall that motivates boosting NAD+ at all is covered in NAD+ and aging.