The short answer: for a daily routine, NMN is the practical choice, and "NAD supplements" sold as oral capsules are mostly selling you an inefficient route to the same place. The longer answer is worth your time, because the reason behind it tells you how to evaluate every other product in this category.
The one-paragraph version
NAD+ is the molecule your cells actually use. NMN is a precursor — a smaller building block your body converts into NAD+. You cannot efficiently swallow NAD+ itself and have it arrive intact, because it is a large, charged molecule that gets broken apart in the digestive tract before absorption. So an oral "NAD+" capsule largely ends up delivering precursors anyway, just less predictably than a product that was designed to deliver precursors in the first place.
What NAD+ actually does
Nicotinamide adenine dinucleotide is a coenzyme present in every living cell, and it does two jobs that are easy to confuse.
The first is the one from biology class. NAD+ shuttles electrons during metabolism, cycling between its oxidised form (NAD+) and its reduced form (NADH). Without it, the reactions that turn food into ATP do not proceed. This role is catalytic — the molecule is recycled rather than used up.
The second job is the one that matters for aging, and it works differently. A group of enzymes does not merely borrow NAD+, it consumes it, cleaving the molecule and leaving a fragment behind. Sirtuins, which regulate a range of stress and metabolic responses, work this way. So do PARPs, which carry out DNA repair. So does CD38, an immune-associated enzyme.
That consumption is the crux of the whole field. Your cells are continuously destroying NAD+ as a cost of doing repair and signalling work, and continuously rebuilding it. Aging shifts that balance.
Why you cannot simply take NAD+
This is the question that sends most people to a page like this one, and the answer is structural rather than controversial.
NAD+ is a dinucleotide: two nucleotides joined by a phosphate bridge. By the standards of things that cross your intestinal wall intact, it is large, and it carries charge. Both properties work against absorption. What appears to happen instead is that NAD+ encountering the digestive tract is progressively broken down — losing phosphate groups and separating — into smaller components, which are then absorbed as the precursors they have become.
Read that again, because it is the entire argument: an oral NAD+ product is a precursor product that took a detour. You are paying for a large molecule to be dismantled into smaller ones, rather than buying the smaller ones directly at a known dose.
What NMN is, and how it gets to NAD+
Nicotinamide mononucleotide is one step down the chain. It is a single nucleotide — roughly half the size of NAD+ — and it sits one enzymatic reaction away from the finished product. Inside the cell, an enzyme called NMNAT attaches the final piece and you have NAD+.
There is a genuine, unresolved scientific argument about the step before that: how NMN crosses into the cell. One model holds that NMN is dephosphorylated outside the cell to nicotinamide riboside (NR), taken in, and then rebuilt. Another points to a dedicated NMN transporter identified in mouse small intestine. The honest position is that both mechanisms have support, the balance between them in humans is not settled, and anyone telling you it is settled is selling something.
Here is why that argument matters less in practice than it sounds: both routes end at the same place. Whether NMN enters directly or arrives via NR, the destination is the NAD+ pool. The pathway dispute is a question about efficiency, not about whether the thing works at all.
The regulatory story you need to know about
For three years, NMN in the United States was in a strange position, and the residue of it is still all over the internet.
In 2022 the FDA took the view that NMN was excluded from the legal definition of a dietary supplement, on the grounds that it had been authorised for investigation as a drug. Under the so-called drug-preclusion rule, that can knock an ingredient out of the supplement category entirely. Retailers pulled listings. Some brands reformulated to NR to stay on the shelf.
That position was reversed. On 29 September 2025, the FDA confirmed that NMN is not excluded from the dietary supplement definition, having concluded there was sufficient evidence NMN was marketed as a supplement in the US before the relevant drug investigation was authorised. Follow-up letters to ingredient suppliers in December 2025 reinstated its New Dietary Ingredient standing.
What that does and does not mean
It means NMN is lawful in US dietary supplements again, and the 2022 cloud is gone. It does not mean NMN is unregulated: it remains a New Dietary Ingredient, which means a supplier still needs an accepted New Dietary Ingredient Notification on file. Self- affirmed GRAS status does not substitute for that. Products without the paperwork are still exposed to enforcement.
Practical consequence for you as a buyer: a large amount of NAD-related content online was written during the exclusion window and still says NMN is banned, restricted or unavailable in the US. It is out of date. Check the date on anything you read about NMN's legal status — including this page, which we will update if the position shifts again.
Side by side
| NAD+ (oral) | NMN | |
|---|---|---|
| What it is | The finished coenzyme | Direct precursor, one step away |
| Molecular size | Dinucleotide — large, charged | Mononucleotide — roughly half |
| Survives digestion intact | Largely no — broken down to precursors | Better, though the entry mechanism is debated |
| Steps to usable NAD+ | Dismantled, absorbed as fragments, rebuilt | One enzymatic step once inside the cell |
| US supplement status | Sold as a supplement | Lawful; NDI notification required (FDA, Sept 2025) |
| Dose transparency | Poor — you cannot know what fraction arrives as what | Good — label dose maps to a known pathway |
| Sensible use | Hard to justify over a precursor | Daily maintenance routine |
So which should you actually take?
If you want one daily thing and no further decisions: a precursor product, taken consistently, at a dose the label actually states. Consistency beats optimisation here by a wide margin — the person who takes a reasonable dose every morning for a year will do better than the person who rotates between three exotic formats for a month each.
If you are drawn to an oral "NAD+" capsule specifically: be clear with yourself about what you are buying. It is not a shortcut past the precursor step. It is the precursor step with less information about the dose.
If your interest is in raising NAD+ as fast and as far as possible rather than maintaining it: oral supplementation of any kind is the wrong tool and you should be reading about infusion and injectable routes instead, with their very different cost and access profile.
The part most comparisons leave out
Raising a measured NAD+ level and producing an outcome you can feel are two different claims, and the evidence is much stronger for the first than the second. Precursor supplementation raising NAD+ markers is reasonably well supported. What that reliably translates to in a healthy adult — in energy, in cognition, in how you age — is a far more open question, and the trials that would settle it are long, expensive and largely not done yet.
We think that is a reason for calibrated expectations, not for dismissal. Taking a precursor is a bet that a well-described mechanism produces a real-world benefit. It is a defensible bet. It is not a settled one, and you should be suspicious of anyone who presents it as one.
What would change our mind
We would revise this page if well-run human trials showed oral NAD+ reaching the bloodstream substantially intact, if the NMN entry mechanism were resolved in a way that materially changed dosing, or if the FDA's September 2025 position were revisited. We will date any such change at the top of the page.
Next: NMN vs NR — the comparison that actually has two defensible answers, or how delivery format changes the maths.