NAD
You cannot buy NAD
Search for it and you get a molecule with two forms. Shop for it and you get a shelf of compounds, none of which is that molecule. Both answers are correct, and the gap between them is where most of the marketing lives.
First tier — the molecule
NAD+ and NADH are one molecule, not two products
NAD is a coenzyme that sits in every cell and shuttles electrons around. NAD+ is the form that has given its electrons away; NADH is the form carrying them. They convert back and forth constantly. It is one substance in two states, not a choice you make at a till.
This is the level everything is measured at — a trial reports what happened to NAD levels. It is not the level you buy at, because the intact molecule is large and poorly absorbed from the gut. So the thing being measured and the thing being sold are never the same thing, which is exactly what makes the category hard to read.
Second tier — what you actually take
Six precursors, and they are not interchangeable
A precursor is something the body converts into NAD. These are what trials administer, so these are what earn a rating here — one each, separately. A trial of nicotinamide riboside tells you nothing about NMN, in the same way a trial of magnesium oxide tells you nothing about magnesium glycinate.
We hold two of the six. The other four are gaps, shown rather than hidden.
The original B vitamin. Cheap, in every B-complex, and the only one here with decades of trial history — though that history is mostly about cholesterol and blood pressure, not ageing.
The one the longevity market ran on. One step closer to NAD than niacin.
The most-studied of the modern precursors and the one most people actually buy. We do not hold it yet.
The amide form of B3. Does not cause the flush niacin does, and is the form used in most skin products.
The reduced form of the molecule itself, sold in stabilised tablets. Whether meaningful amounts survive digestion is the whole question.
The amino acid your body can build NAD from without any precursor at all, through the de novo pathway. Usually left out of the conversation because nobody markets it this way.
Read the ratings carefully
Niacin’s strongest result here is for blood pressure, at pharmacological doses, and it has nothing to do with ageing or NAD levels. Pointing at that rating to support a longevity claim would be borrowing evidence from a different question — the commonest way this category gets oversold.
And NMN’s two ratings each rest on a single paper. That is enough to say something, not enough to say much.
Third tier — the bottle in your hand
A product is a precursor, at an amount
The bottle is where the question finally becomes answerable. It names one of the six above, at some number of milligrams, and that number decides whether any of the research applies to what you bought.
It is also where most of the disappointment is. A B-complex carrying 100 mg of niacin is not a longevity product, whatever the shelf-talker says, and a bottle at a fraction of a trial dose is a different proposition from the trial.
Check a bottle against the research →
And the drip, which is none of the three
NAD+ given intravenously skips the absorption problem entirely, which is the point of it. That makes it a procedure rather than a supplement, with its own costs, risks and evidence.
NAD+ Intravenous Therapy →Ratings on this page are computed from the papers behind each claim, the same as everywhere else on the site — see how a claim earns its rating. The four precursors we do not hold have not been researched yet; they are listed so the gap is visible, not because we have an opinion about them.