NAD+: a number that rises, in a place nobody is asking about

The short version

NAD+ is not really a peptide. It is a coenzyme, a small helper molecule that every cell uses to shuttle electrons through the reactions that produce energy, and that a set of repair and signalling enzymes consume as a raw material ^[16]. It sits on this desk because it is sold, injected and argued about in exactly the same market as the peptides here.

The reasoning behind it is easy to follow. Tissue NAD+ falls with age. Several important enzymes, including the sirtuins and the DNA-repair enzyme PARP1, need NAD+ to work, and they compete for the same pool with an enzyme called CD38 that rises with age and inflammation ^[16]. So topping the pool back up sounds like a sensible intervention.

What has actually been shown is narrower. Oral precursors raise NAD+ in blood, reliably and in proportion to the amount taken: nicotinamide riboside raised whole-blood NAD+ by 22, 51 and 142 percent at three ascending amounts over eight weeks ^[17], and nicotinamide mononucleotide raised it significantly at every amount tested over 60 days ^[14]. That part is not in dispute.

The gap is the distance between that blood number and the claim it is used to support. A 2025 review of the human evidence concluded that clinical efficacy has been limited, that age-related NAD+ decline has been consistently observed only in a limited number of human studies, and that data on tissue-specific NAD+ remain sparse ^[13]. In plain terms: the measurement stops in the blood, and the hypothesis is about the tissues.

What it is

The full name is nicotinamide adenine dinucleotide. Structurally it is two nucleotides joined by a pair of bridging phosphate groups, one carrying a nicotinamide ring and the other an adenine ring, with the molecular formula C21H27N7O14P2. It exists in an oxidised form, NAD+, and a reduced form, NADH, and the ratio between them is one of the central dials of cell metabolism.

In practice, three different things get sold under this heading and they are not interchangeable. NAD+ itself is offered as an oral capsule and as an intravenous infusion. Nicotinamide mononucleotide, or NMN, and nicotinamide riboside, or NR, are precursors: smaller molecules the body converts into NAD+ through a salvage pathway. Nearly all of the credible human trial evidence concerns the precursors rather than NAD+ taken directly, and one of the field's own long-running arguments is that oral NAD+ is poorly taken up intact, making plain NAD+ capsules the least defensible product of the three.

Regulatory status is messy and unfinished. NAD+ and its precursors are sold as dietary supplements rather than approved drugs. NMN in particular is contested: the FDA has taken the position that it is excluded from the dietary-supplement definition because it was first investigated as a drug, which has left its market position unresolved. Injectable NAD+ is typically compounded rather than approved, and has been subject to a Class I recall over elevated bacterial endotoxin, the most serious recall category the agency issues. Supplement-grade purity varies and third-party testing is not guaranteed. None of these are findings about the molecule; all of them are reasons a reader cannot assume the product matches the studies.

How it works

NAD+ has two jobs, and confusing them is the source of most of the overreach around it.

The first job is bookkeeping. In glycolysis, the citric acid cycle and oxidative phosphorylation, NAD+ picks up electrons, becomes NADH, drops them off and becomes NAD+ again. Nothing is used up. A cell needs a working pool, not a growing one, and past a certain point more does not mean faster.

The second job is different in kind: NAD+ is consumed as a substrate by a group of signalling enzymes. The sirtuins, a family of seven, use it to strip chemical tags off proteins and thereby influence gene expression and metabolism. PARP1 uses it in the response to DNA damage. CD38 and its relative CD157 sit on cell surfaces and break it down, and their activity rises with age and inflammation ^[16]. Because these enzymes draw on the same pool, they compete, and a pool that shrinks with age is the mechanistic core of the whole NAD+ story.

So the intervention logic runs: give a precursor, raise the pool, let the sirtuins and PARPs work again. Each step of that chain has different evidential support. The first step is well demonstrated in humans ^[14][17]. The second is demonstrated in blood and thinly measured in tissue ^[13]. The third, that the downstream enzymes then do measurably more useful work in a person, is where the human evidence runs out.

What the research shows, and what each study leaves open

Nicotinamide riboside safety and dose-response, 2019. Healthy overweight adults took 100, 500 or 1000 mg daily for eight weeks. Whole-blood NAD+ rose by 22, 51 and 142 percent respectively and stayed elevated for the duration, with no flushing, no significant difference in adverse events against placebo, no rise in LDL cholesterol and no disruption of one-carbon metabolism ^[17]. Left open: eight weeks, healthy participants, and a blood measurement as the primary result. This trial establishes that the pool can be raised safely. It does not test whether raising it does anything.

Nicotinamide mononucleotide multicentre trial, 2023. Middle-aged adults took 300, 600 or 900 mg daily for 60 days in a double-blind randomised trial. Blood NAD+ rose significantly against placebo at days 30 and 60 across all groups, walking distance and quality-of-life scores improved, a biological-age measure did not increase, 600 mg daily was identified as the optimal amount, and no safety issues appeared at any amount ^[14]. Left open: 60 days. Walking distance and questionnaire scores are soft endpoints in an unblinded-feeling context, and a biological-age index that fails to rise is a weaker result than one that falls.

Muscle insulin sensitivity, 2021. Prediabetic postmenopausal women took 250 mg of NMN daily for ten weeks. Muscle insulin sensitivity, measured by the hyperinsulinaemic-euglycaemic clamp, the reference method, improved significantly, and insulin signalling in muscle was remodelled. Body composition did not change and HbA1c did not change ^[15]. Left open: this is the most rigorous positive endpoint in the whole NAD+ human literature, and it is worth noting exactly what it did and did not move. A clamp measurement improved; the two clinically familiar measures alongside it did not. The participants were also a specific group, prediabetic and postmenopausal, which is not the group buying the supplement.

Foundational review, 2021. NAD+ levels decline with age across yeast, worms, mice and humans, and the review identifies the enzymes competing for the pool, the sirtuins, the PARPs and CD38 and CD157, framing restoration as a candidate strategy against age-related disease ^[16]. Left open: it is a review, and much of its strength comes from model organisms. That is where the strongest anti-ageing NAD+ data still are.

The 2025 assessment. A narrative review of the human clinical evidence on NAD+ precursor supplementation in ageing concluded that human trials have shown limited efficacy, that age-related NAD+ decline has been consistently observed in only a limited number of human studies, and that the body of data on tissue-specific NAD+ dynamics remains sparse. It called for more clinical study of systemic and tissue-specific NAD+ metabolism rather than continued reliance on extrapolation from rodents ^[13]. Left open: this is the field auditing itself, and it is the most important citation on this page. It says the premise is thinly measured in humans and the payoff is unproven, while the intermediate step is well established.

Reported effects, cautions and disputes

Unlike the injectable peptides on this desk, the source set behind this page carries no compiled record of community-reported effects for NAD+, so none is presented here. Absence of a compilation is not evidence that nothing is reported; it means this desk has nothing verified enough to summarise, and inventing the missing paragraph would be exactly the failure this site is written against.

What the literature does carry is a set of live disputes, and they are worth more than a testimonial anyway.

• Oral NAD+ itself is the weakest of the three products. NAD+ is poorly taken up by cells intact, which is why precursors are the rational oral route and why plain NAD+ capsules are widely argued to be largely ineffective.
• The blood-to-outcome step is unproven in humans. Raising blood NAD+ is well demonstrated ^[14][17]; translation into longevity or disease prevention is not, and the 2025 review says so directly ^[13].
• The strongest anti-ageing data are still rodent data ^[16], and the same review warns against extrapolating from them ^[13].
• Intravenous NAD+ is marketed far ahead of its evidence. Controlled evidence for wellness infusions is minimal, infused NAD+ clears from plasma rapidly, and infusions run too fast are described as causing chest or abdominal discomfort, flushing and nausea.
• Compounded injectable NAD+ has a documented manufacturing failure. The FDA issued a Class I recall of a compounded NAD+ injection for elevated bacterial endotoxin. That is a supply-chain risk, not a pharmacological one, and it is the kind that unregulated injectables carry generally.
• A theoretical concern exists in cancer. NAD+ supports the metabolism of proliferating cells, and its role in oncology is dual and context-dependent, so caution is advised in cancer populations. This is mechanism-based reasoning rather than a human finding.
• The regulatory position of NMN is unresolved, and supplement-grade purity and actual content vary between products with no guaranteed third-party testing.

One further gap deserves naming because nobody advertises it. Every human trial summarised above ran between eight weeks and sixty days ^[14][15][17]. The hypothesis those trials are motivated by concerns what happens to a body over thirty years. No trial in this literature has run anywhere near long enough to test the claim that sells it, and none is designed to.

Where it fits in the gap register

NAD+ is the compartment case. It is the only entry on this desk where the headline measurement is not disputed at all and still does not establish the thing it is quoted for. Nicotinamide riboside really does raise whole-blood NAD+ by up to 142 percent ^[17]. That is a clean, replicated, dose-dependent human result. It simply is not an answer to the question people are buying it to answer.

Set against retatrutide, the difference in kind is clear. Retatrutide's surrogates, weight and HbA1c, are at least measured in the tissue and system of interest, and the missing step is time and outcome. NAD+'s surrogate is measured in a different compartment from the one the hypothesis lives in, and the field's own 2025 review says the tissue data needed to bridge that are sparse ^[13]. Against BPC-157 the contrast is sharper still: BPC-157 lacks human data, while NAD+ has human data that answers an adjacent question.

There is also a population gap here that goes largely unremarked. The most rigorous positive human endpoint in this literature came from prediabetic postmenopausal women ^[15], and the multicentre trial studied middle-aged adults ^[14]. Neither group matches the healthy person taking a precursor in the hope of ageing more slowly, and no trial has yet studied that person with an endpoint that would settle the question. See the comparison page for how the four gaps stack up.