THE 30-SECOND OVERVIEW
At a glance
NAD+, NMN and NR get discussed as if they were interchangeable versions of one supplement. Chemically they are three distinct molecules at three different points of one biosynthetic pathway, and the differences between them decide almost everything else: how they are absorbed, what the human trials actually tested, and what a research protocol built around each one can claim.
Three molecules, one pathway
NAD+, nicotinamide adenine dinucleotide, is the endpoint. It is a dinucleotide, two nucleotides joined through their phosphate groups, and it is one of the busiest molecules in biology: the central electron carrier of metabolism and the required substrate for sirtuins and PARP enzymes. It is also large, charged, and unstable in solution, and the intact molecule does not readily cross cell membranes.
NMN, nicotinamide mononucleotide, is one step upstream. It is a single nucleotide: nicotinamide, a ribose sugar, and a phosphate group. The enzyme NMNAT converts NMN directly into NAD+.
NR, nicotinamide riboside, is one step further back. It is a nucleoside, which means the same nicotinamide and ribose but without the phosphate. Nicotinamide riboside kinases (NRK1 and NRK2) phosphorylate NR into NMN, which then becomes NAD+.
So the chain is NR to NMN to NAD+, with each step adding one piece. That phosphate group, the only chemical difference between NR and NMN, turns out to matter a great deal.
Why the phosphate matters for absorption
Small uncharged molecules cross membranes far more easily than phosphorylated ones. NR, without the phosphate, is taken up by cells through nucleoside transporters, and Trammell and colleagues showed in 2016 that oral NR is bioavailable in both mice and humans and raises blood NAD+ metabolites.
NMN's route in is less settled. A dedicated transporter, Slc12a8, was reported by Grozio and colleagues in 2019, but the finding has been contested, and a substantial body of work suggests much oral NMN is first converted to NR outside the cell, absorbed as NR, and then rebuilt. Either way NMN reaches the same destination; the argument is about the door it uses.
Direct NAD+ faces the hardest problem of the three. The intact dinucleotide is not meaningfully absorbed by cells as such, which is precisely why the research field went the precursor route, and why the human evidence base belongs almost entirely to NR and NMN rather than to NAD+ itself.
What the human trials actually tested
The distinction shows up clearly in the trial record.
For NR, Martens and colleagues ran a placebo-controlled crossover in healthy middle-aged and older adults in 2018 using 1000mg per day for six weeks, and reported raised blood NAD+ with good tolerability. Other NR trials span roughly 100mg to 1000mg daily, and dose-dependent elevation of blood NAD+ is the consistent finding.
For NMN, Yoshino and colleagues published a placebo-controlled trial in Science in 2021 using 250mg daily in prediabetic postmenopausal women over ten weeks, reporting improved muscle insulin sensitivity. Most other NMN trials also sit in the low hundreds of milligrams. The NMN record is younger and smaller than the NR record.
For direct NAD+, there is no comparable oral trial. Intravenous NAD+ has been used clinically, but published protocols are sparse and heterogeneous. Whether intranasal delivery changes the picture is an open research question rather than an answered one, which is the honest framing for formats like our NAD+ nasal spray.
What raising blood NAD+ does and does not establish
Every claim above is about a marker: NAD+ measured in blood. Blood is accessible, not necessarily representative. The mechanistic hypotheses about sirtuins, mitochondria and ageing concern NAD+ inside tissues, and raising a blood level is not the same claim as changing tissue biology. Trial durations have been weeks, not years, so long-term questions remain open in both directions.
It is also worth saying plainly that NR and NMN are not milligram-for-milligram equivalent. They enter the salvage pathway at different points, their absorption routes differ, and the trials that used them differ in population and endpoint. Treating a result from one as evidence about the other is an assumption the literature does not license.
The takeaway
NR is a nucleoside, NMN is its phosphorylated nucleotide, and NAD+ is the finished dinucleotide both feed into. The human trial record belongs to the two precursors: NR with the larger and older dataset, NMN with the smaller and newer one, and direct NAD+ with almost none. We stock all three as separate research lines, NMN, NR, and NAD+ in several formats, precisely because the literature treats them as three different compounds. A protocol should too.
All products are intended for research use only. Not for human consumption. Must be 21 years of age or older to purchase.
References
1. Trammell, S. A., Schmidt, M. S., Weidemann, B. J., et al. (2016). Nicotinamide riboside is uniquely and orally bioavailable in mice and humans. Nature Communications, 7, 12948.
2. Martens, C. R., Denman, B. A., Mazzo, M. R., et al. (2018). Chronic nicotinamide riboside supplementation is well-tolerated and elevates NAD+ in healthy middle-aged and older adults. Nature Communications, 9(1), 1286.
3. Yoshino, M., Yoshino, J., Kayser, B. D., et al. (2021). Nicotinamide mononucleotide increases muscle insulin sensitivity in prediabetic women. Science, 372(6547), 1224-1229.
4. Grozio, A., Mills, K. F., Yoshino, J., et al. (2019). Slc12a8 is a nicotinamide mononucleotide transporter. Nature Metabolism, 1(1), 47-57.
