If you’re serious about longevity, you’ve heard about NAD+. And if you’ve tried to research it, you’ve run into a wall of conflicting claims about NMN vs NR — which form is better, whether NMN can even be absorbed orally, whether the whole thing is overhyped.
I’ve been running NAD+ precursors since 2018. I’ve tried both forms, tracked my bloodwork obsessively, and read the primary research rather than supplement company marketing. Here’s what I actually think.
The NAD+ Problem: Why You Need to Supplement
NAD+ (nicotinamide adenine dinucleotide) is a coenzyme present in every cell in your body. It’s essential for ATP production in the mitochondria, DNA repair via PARP enzymes, sirtuin activation (the longevity genes), and the circadian clock.
The problem is that NAD+ levels decline with age. By your 50s, you have roughly half the NAD+ you had at 20. This decline correlates with essentially every major marker of biological aging: reduced energy production, impaired DNA repair, mitochondrial dysfunction, metabolic slowdown.
You can’t supplement NAD+ directly in any useful way — it doesn’t survive digestion and doesn’t cross cell membranes efficiently. Instead, you supplement precursors that your cells convert into NAD+. The two main options are NR (nicotinamide riboside) and NMN (nicotinamide mononucleotide).
NR: Nicotinamide Riboside
NR is one step back from NAD+ in the biosynthetic pathway. It enters cells via specific nucleoside transporters (Slc29a1/2 in mice, similar transporters in humans), then gets phosphorylated to NMN inside the cell, then converted to NAD+.
NR has the best clinical evidence base of either compound. ChromaDex’s Tru Niagen product (250mg NR) has been through multiple human clinical trials showing 40–90% increases in blood NAD+ levels. The data is genuinely solid — dose-dependent, reproducible, peer-reviewed.
NR is also more affordable than NMN. A meaningful dose (300–500mg/day) costs significantly less with NR than equivalent NMN.
NMN: Nicotinamide Mononucleotide
NMN is one step closer to NAD+ than NR. It needs to be converted to NR to enter most cells, then back to NMN inside the cell, then to NAD+. Sounds redundant — and for most tissues, it probably is.
However, there’s a critical exception: skeletal muscle. Mouse studies from Shin-ichiro Imai’s lab at Washington University showed that NMN enters muscle cells directly via a specific transporter (Slc12a8) that NR cannot use. This means for muscle tissue NAD+ repletion specifically, NMN may have an advantage NR cannot match regardless of dose.
David Sinclair at Harvard runs 1g NMN daily alongside resveratrol and metformin. He’s been public about this for years. Whether that personal protocol proves efficacy is debatable, but it put NMN on the map and drove an enormous amount of follow-up research.
Human clinical data for NMN was sparse until 2021–2023. A 2021 study in Science showed that oral NMN was safe and elevated blood NAD+ in healthy older men. A 2023 trial showed meaningful improvements in muscle function and NAD+ levels in older adults at 250mg/day. The evidence is catching up to the hype.
The Bioavailability Debate
The biggest knock on NMN was a 2022 preprint suggesting that orally administered NMN can’t actually be absorbed from the gut as NMN — it gets broken down to NR and nicotinamide before absorption. If true, this would make NMN equivalent to NR at best, and potentially worse because you’re paying more for essentially the same precursor.
The counter-evidence: the Slc12a8 NMN transporter exists in intestinal tissue in mice. If humans have an equivalent transporter — which is plausible but not yet confirmed — some fraction of oral NMN may be absorbed intact. The 2021 Science trial showed elevated NMN in blood after oral supplementation, suggesting at least partial intact absorption.
The verdict: genuinely unresolved. Both compounds reliably raise blood NAD+ levels. Whether the pathway matters for specific tissue outcomes (especially muscle) requires more human data than we currently have.
My Protocol: What I Actually Take
I use NMN at 1g/day, sublingual. The sublingual delivery bypasses the GI absorption debate entirely — dissolve under the tongue, absorb directly into the bloodstream. The trade-off is taste (NMN is bitter) and slightly higher cost per gram than capsules.
I take it in the morning, fasted, before training. Timing matters: NAD+ is involved in circadian rhythm regulation. Morning dosing keeps the NAD+ peak aligned with daytime activity. Evening dosing may disrupt sleep quality by activating sirtuin pathways that are supposed to be downregulated at night.
Full longevity stack context:
- NMN: 1g sublingual, morning
- Resveratrol: 500mg with fat source (olive oil, avocado), same time — Sinclair’s protocol, resveratrol activates sirtuins that NAD+ then fuels
- Metformin: 500mg with evening meal (I cycle this — use for 3 months on, 1 month off)
- Rapamycin: 5mg weekly (separate protocol — full rapamycin guide here)
I’ve been running some version of this stack for 3 years. Bloodwork consistently shows excellent mitochondrial function markers, no negative metabolic effects from metformin, and energy levels that don’t match my calendar age.
Should You Use NMN or NR?
Honest answer: if budget is a concern, start with NR. The clinical evidence is stronger, the cost is lower, and it reliably raises NAD+ levels. 300–500mg NR daily is well-supported by human data.
If you’re optimizing specifically for muscle function and metabolic performance — which is my priority — or if you want to match what the most aggressive longevity researchers are doing themselves, NMN at 500mg–1g daily makes sense. Use sublingual delivery if you want to sidestep the bioavailability controversy entirely.
Don’t bother with combination products that give you 100mg NMN + 100mg NR. Underdosed marketing products. Effective doses in studies are 250mg+; for real optimization, I’d argue 500mg minimum for either compound.
What to Expect: Honest Results
The effects of NAD+ precursors are subtle compared to compounds with more dramatic pharmacology. You’re not going to feel a hit the way you feel first-dose effect from a GHRH peptide or notice body composition shift the way you do on a SARM cycle.
What I notice consistently:
- Sustained energy — not stimulant energy, but the absence of afternoon crashes and a more consistent energy curve throughout the day
- Training recovery — I recover from sessions faster, which I attribute partly to NAD+ and partly to the full recovery stack I run
- Sleep quality improvements — this was the most surprising consistent finding. Better deep sleep metrics (I track with Oura) within 3–4 weeks of consistent use
- Cognitive sharpness — harder to measure objectively, but I work faster and more clearly on training days when my NAD+ supplementation is consistent
None of these are dramatic. NAD+ optimization is infrastructure, not acceleration. You’re building the foundation that every other intervention runs on more effectively.
Safety
Both NMN and NR have clean safety profiles in published human trials up to 2000mg NR and 1200mg NMN without adverse events. One theoretical concern worth mentioning: high-dose niacinamide (which both compounds convert through) can inhibit sirtuins at very high doses. At typical supplemental doses (500mg–1g), this doesn’t appear to be a practical issue.
There’s a theoretical cancer concern similar to any pro-growth pathway — NAD+ supports rapid cell division, which is also what cancer cells need. The clinical evidence on this in humans is reassuring but long-term data is limited. I’m not particularly concerned at the doses I use, but it’s worth noting.
Bottom Line
Both work. NR has more clinical backing and costs less. NMN has theoretical advantages for muscle tissue and is what the most serious longevity researchers use personally. I use NMN. If you want a place to start, NR at 300–500mg is lower risk and lower cost. If you want to optimize, NMN at 500mg–1g sublingual with morning resveratrol is the protocol I’d point you toward.
NAD+ optimization is a long game. Give it 60–90 days before evaluating. Track your energy, sleep, and recovery — not your body weight or mirror reflection. That’s where you’ll see it.