Start with the thing most pages about this leave out: NAD+ is not a peptide. It is a dinucleotide, a coenzyme built from nicotinamide and adenine, and it sits in this catalogue because it is sold through the same channels, injected by the same clinics and discussed in the same rooms as everything else here, not because it belongs to the same chemical family.

NAD+ is genuinely essential. Every cell uses it as the electron carrier in energy metabolism, and it is consumed as a substrate by two families of enzymes, the sirtuins and the PARPs, that sit close to a lot of ageing biology. Tissue NAD+ falls with age. That single observation is what the entire commercial category rests on.

What is sold divides into two very different things, and the split matters more than anything else on this page: oral precursors (nicotinamide riboside, NR, and nicotinamide mononucleotide, NMN) and intravenous NAD+ itself. Almost all the human evidence is about the first. Almost all the money is in the second.

NAD+ cycles between oxidised and reduced forms to carry electrons in metabolism, and separately is cleaved as a substrate by sirtuins and PARPs, which is why anything that consumes it heavily, including DNA damage repair, lowers the pool.

The route question is the one that decides everything. NAD+ is a large, charged molecule and does not cross cell membranes freely. Cells make their own from precursors. So an oral or intravenous dose of NAD+ itself is not a delivery of NAD+ to the inside of a cell; it is degraded outside the cell to smaller precursors which are then taken up and rebuilt.

That is the mechanistic argument for giving precursors rather than the molecule, and it is also the reason the intravenous product is a strange one: it is the most expensive way to deliver something the body was going to have to break down first anyway.

The evidence divides exactly where the products do, and it is much stronger on the side people spend less money on.

That precursors raise NAD+ is well established. Randomised placebo-controlled trials of nicotinamide riboside in healthy middle-aged and older adults report a clear, dose-dependent rise in blood NAD+, with good tolerability. NMN trials report the same. This part is not in dispute.

That raising it changes anything a person experiences is much less clear. This is the same error pattern that runs through several entries here: a biomarker moved is not an outcome achieved. Trials that looked past the blood level have reported modest and inconsistent results. NMN work in older adults has reported effects on measures like walking speed, in small trials. Work in aged skeletal muscle found NR raised the muscle NAD+ metabolome and shifted transcriptomic signatures without delivering the functional gains the mechanism predicted.

For intravenous NAD+, the route actually marketed, there is very little. A recent systematic review of NAD+ supplementation for ageing and wellness found the clinical literature dominated by short trials of oral precursors with heterogeneous endpoints, and nothing approaching an adequate evidence base for infusion. The registry holds hundreds of entries mentioning NAD+, and reading what they administer rather than counting them is the necessary step.

Oral precursors have been well tolerated across the trials that exist, which are mostly weeks to a few months in healthy adults. Reported effects are mild and gastrointestinal. That is a reasonable safety record for the exposures studied and says nothing about years.

Intravenous administration is a different question and carries the risks of any infusion given outside a hospital: infusion reactions, and the contamination and dosing-error risks of a product prepared in a clinic rather than manufactured. Rapid infusion is commonly reported to cause chest tightness, nausea and flushing, which is why these drips are given slowly over hours.

The mechanistic caution worth naming is the same one that applies to anything proposed to accelerate cell maintenance. NAD+ is a substrate for PARPs in DNA repair and for sirtuins, and both sit close to cell survival and proliferation. Raising a substrate for those pathways over long periods has not been characterised for cancer risk in either direction, and the honest position is that nobody knows rather than that it is safe.

Nothing here is approved as a medicine for ageing, energy or cognition in any major jurisdiction.

The routes have sharply different statuses and this is where most confusion sits. Nicotinamide riboside is sold as a dietary supplement in the United States and holds GRAS status for food use. NMN's position is different and worth knowing: the US FDA has taken the position that NMN is excluded from the dietary supplement definition because it was authorised for investigation as a new drug, which has moved products off shelves and is actively contested by industry.

Intravenous NAD+ is not an approved product. It is compounded and administered by clinics, which is a different regulatory pathway from a drug approval and is frequently presented as though it were the same thing.