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NAD+ vs NMN vs NR — Trial Data

NMN and NR are precursors to NAD+, not NAD+ itself — and that distinction turns out to matter mechanistically. This page reports why, what human trial evidence exists for each form, and where that evidence is thin, each figure attributed to the study that reported it.

On this page
  1. 1.Mechanism
  2. 2.Human Evidence, by Form
  3. 3.The Closest Thing to a Head-to-Head
  4. 4.Adverse Events
  5. 5.Evidence Level
  6. 6.FAQ
  7. 7.References

Mechanism

NAD+ (nicotinamide adenine dinucleotide) is a coenzyme required by sirtuin enzymes, PARP (DNA-repair) enzymes, and mitochondrial energy metabolism. As a large pyridine dinucleotide, it is not reported to cross the gut wall or a cell membrane intact when taken orally or delivered extracellularly.

Kulikova et al. 2019 (Metabolites, PMID 31795381), working with human HEK293 cells, found that exogenous NAD+ is cleaved by cell-surface enzymes to NMN (nicotinamide mononucleotide), which is then further cleaved to NR (nicotinamide riboside) — and that this reduction to NR is a prerequisite for the material to reach intracellular NAD+ synthesis, since NR is what actually crosses the cell membrane via nucleoside transporters. In other words: giving a cell NAD+ directly does not skip the precursor pathway, it starts it one step earlier, with a breakdown step in between.

NMN and NR are therefore studied and sold as the functional oral forms, while intact NAD+ is mostly delivered where the absorption problem can be bypassed — IV infusion — or sold as an oral capsule despite it.

Human Evidence, by Form

NAD+NMNNR
What it isThe intact coenzyme molecule itselfNicotinamide mononucleotide — one biosynthetic step from NAD+Nicotinamide riboside — a smaller precursor, one step further upstream
Crosses the gut wall / cell membrane intact?No — established in vitro (Kulikova et al. 2019): extracellular NAD+ is cleaved to NMN, then to NR, before cellular uptakePartial — absorbed partly intact, partly hydrolyzed to NR first, per the mechanism section belowYes — enters cells via nucleoside transporters, the route NAD+ and NMN are ultimately reduced to
Completed human RCT raising blood NAD+None identified for this page — two oral NAD+ trials are registered but not yet reporting results (see below)Yoshino et al. 2021 (PMID 33888596); Igarashi et al. 2022 (PMID 35927255)Martens et al. 2018 (PMID 29599478)
Typical route in practiceIV infusion (unregulated wellness-clinic setting) or oral capsule sold despite the absorption problem aboveOral capsuleOral capsule
Reported tolerabilityIV: significant infusion-related adverse effects reported in a small retrospective pilot (Reyna et al. 2026) — see Adverse EventsNo significant increase in adverse events across a 15-trial meta-analysis (Yang et al. 2026, PMID 42514320)Well tolerated across its cited RCTs
Regulatory statusSold as a dietary supplement (oral) or offered off-label in wellness/IV-therapy settings; neither route is FDA-approved as a drugSold as a dietary supplement in the US; the FDA notified sellers in November 2022 that NMN is excluded from the dietary-supplement definition, though enforcement has been minimalSold as a dietary supplement in the US; no comparable FDA exclusion notice identified

NAD+ itself: no completed randomized controlled trial of oral NAD+ with reported blood-level or efficacy outcomes was identified for this page. Two are registered and running — NCT07692633 (absorption, safety and efficacy of an oral NAD+ supplement) and the RENEWAL-NAD+ study (NCT06882096) — but neither had posted results as of this page’s last review. The nearest human data is a small retrospective IV-infusion pilot, covered in the head-to-head section below.

NMN: Yoshino et al. 2021 (Science, PMID 33888596) randomized postmenopausal women with prediabetes who were overweight or obese to 10 weeks of oral NMN or placebo, double-blind, and reported increased insulin-stimulated glucose disposal (hyperinsulinemic-euglycemic clamp) and skeletal-muscle insulin signaling with no change under placebo. Igarashi et al. 2022 (NPJ Aging, PMID 35927255) randomized healthy older men to 12 weeks of oral NMN or placebo, double-blind, and reported elevated blood NAD+ alongside improved walking speed and grip strength.

NR: Martens et al. 2018 (Nat Commun, PMID 29599478) is a randomized, double-blind, placebo-controlled crossover trial (2×6 weeks) of NR in healthy middle-aged and older adults, reporting good tolerability and effective NAD+ metabolism elevation.

The Closest Thing to a Head-to-Head

No randomized trial has dosed NAD+ itself against NMN or NR in the same participants. The nearest human comparison involving NAD+ directly is Reyna et al. 2026 (Frontiers in Aging, DOI 10.3389/fragi.2026.1652582) — a retrospective electronic-medical-record review from a single commercial wellness clinic, not a randomized trial. It compared four consecutive days of 500 mg IV NAD+ (n=6) against 500 mg IV NR (n=8), both diluted in 500 mL saline, with a 30-day follow-up.

Result: all six NAD+ recipients reported infusion-related adverse effects (detailed below); none of the eight NR recipients did. NAD+ infusions also ran longer on average (97 ± 56 minutes vs 37 ± 13 minutes for NR), which the authors attribute to clients self-slowing the infusion rate in response to symptoms. This is a tiny, uncontrolled, single-site retrospective pilot — it does not carry the weight of the double-blind RCTs cited for NMN and NR above — but it is the most direct human evidence located comparing NAD+ itself against a precursor form.

Adverse Events

NAD+ (IV): Reyna et al. 2026 reports all six NAD+ IV recipients in their retrospective pilot experienced “moderate to severe abdominal cramping, diarrhea, nausea, vomiting, increased heart rates, pain in throat, congestion, and chest pressure” during infusion, which resolved immediately once the infusion ended. No comparable adverse-event data for oral NAD+ was identified, since no completed oral-NAD+ RCT was located for this page.

NMN: Yang et al. 2026 (Nutrients, PMID 42514320), a systematic review and meta-analysis of 15 randomized controlled trials (10 contributing safety data; doses 250–2,000 mg/day oral, durations 14 days to 24 weeks), found NMN did not increase overall, serious, withdrawal-related, or system-specific adverse events, and did not significantly elevate liver enzymes (ALT/AST).

NR: Martens et al. 2018 reports NR was well tolerated across the trial's two 6-week oral supplementation periods.

Evidence Level

NAD+ itself: thin. The absorption mechanism rests on In Vitro human-cell data (Kulikova et al. 2019); the only human data located touching NAD+ directly is a Human Observational retrospective pilot with n=6 in the NAD+ arm (Reyna et al. 2026), not a controlled trial. Two oral-NAD+ RCTs are registered but not yet reporting. NMN: Human RCT, double-blind (Yoshino et al. 2021, Igarashi et al. 2022). NR: Human RCT, double-blind crossover (Martens et al. 2018).

The evidence base is not symmetric across these three forms. NMN and NR each have a double-blind, placebo-controlled human RCT measuring blood NAD+ and tolerability. NAD+ itself does not — what exists is an in vitro mechanism explaining why it likely can’t be absorbed intact, plus a tiny, uncontrolled retrospective chart review of IV infusions at one clinic. Two registered oral-NAD+ trials may close this gap; until they report, statements about NAD+ itself on this page are mechanistic and observational, not RCT-confirmed.

FAQ

Why can't you just take NAD+ itself instead of a precursor?

Mechanistically, oral or extracellular NAD+ is not taken up by cells intact. Kulikova et al. 2019 (Metabolites, PMID 31795381), working with human HEK293 cells, found that exogenous NAD+ is cleaved by cell-surface enzymes to NMN, which is then further cleaved to NR — and that this stepwise breakdown to NR is a prerequisite for the material to reach intracellular NAD+ synthesis at all. NAD+ itself, as a large pyridine dinucleotide, does not cross the gut wall or a cell membrane the way its smaller precursors do.

Is there a completed human trial testing oral NAD+ itself?

Not one identified for this page with reported results. Two studies registered on ClinicalTrials.gov — NCT07692633 (absorption, safety and efficacy of an oral NAD+ supplement) and the RENEWAL-NAD+ study (NCT06882096, tracing the metabolic flux of orally administered NAD+ precursors) — are testing this question directly, but neither had posted results as of this page’s last review. This is a real evidence gap, not an oversight: the trials that exist for NMN and NR (below) do not exist yet for intact oral NAD+.

What about NAD+ IV infusions — is there human data on those?

A small amount. Reyna et al. 2026 (Frontiers in Aging, DOI 10.3389/fragi.2026.1652582) is a retrospective chart review from a single commercial wellness clinic comparing four consecutive days of 500 mg IV NAD+ (n=6) against 500 mg IV NR (n=8). All six NAD+ recipients reported adverse infusion-related effects; none of the NR recipients did. This is a tiny, uncontrolled, non-randomized retrospective pilot from one clinic — not the kind of evidence the NMN and NR trials below provide — but it is the most direct human data located comparing NAD+ itself against a precursor.

What does the NMN human trial evidence show?

Two double-blind, placebo-controlled RCTs. Yoshino et al. 2021 (Science, PMID 33888596) randomized postmenopausal women with prediabetes to 10 weeks of oral NMN or placebo and reported increased insulin-stimulated glucose disposal and skeletal-muscle insulin signaling. Igarashi et al. 2022 (NPJ Aging, PMID 35927255) randomized healthy older men to 12 weeks of oral NMN or placebo and reported elevated blood NAD+ and improved walking speed and grip strength. Both measure NMN, not intact NAD+.

What does the NR human trial evidence show?

Martens et al. 2018 (Nat Commun, PMID 29599478) is a randomized, double-blind, placebo-controlled crossover trial (two 6-week periods) of oral NR in healthy middle-aged and older adults. It reports NR was well tolerated and effectively elevated whole-blood NAD+ metabolism.

References

  1. Kulikova V, Shabalin K, Nerinovski K, et al. Degradation of Extracellular NAD+ Intermediates in Cultures of Human HEK293 Cells. Metabolites. 2019;9(12):293. https://pubmed.ncbi.nlm.nih.gov/31795381/
  2. Yoshino M, Yoshino J, Kayser BD, et al. Nicotinamide mononucleotide increases muscle insulin sensitivity in prediabetic women. Science. 2021;372(6547):1224-1229. https://pubmed.ncbi.nlm.nih.gov/33888596/
  3. Igarashi M, Nakagawa-Nagahama Y, Miura M, et al. Chronic nicotinamide mononucleotide supplementation elevates blood nicotinamide adenine dinucleotide levels and alters muscle function in healthy older men. NPJ Aging. 2022;8(1):5. https://pubmed.ncbi.nlm.nih.gov/35927255/
  4. Martens CR, Denman BA, Mazzo MR, et al. Chronic nicotinamide riboside supplementation is well-tolerated and elevates NAD+ in healthy middle-aged and older adults. Nat Commun. 2018;9(1):1286. https://pubmed.ncbi.nlm.nih.gov/29599478/
  5. Reyna K, Heinzen G, Patel N, et al. Intravenous infusion of nicotinamide adenine dinucleotide (NAD+) versus nicotinamide riboside (NR): a retrospective tolerability pilot study in a real-world setting. Front Aging. 2026. https://doi.org/10.3389/fragi.2026.1652582
  6. Yang W, Huang J, Tang Z, Chen C, Sun Y. Safety and Metabolism-Related Outcomes of Oral Nicotinamide Mononucleotide Supplementation in Adults: A Systematic Review and Meta-Analysis. Nutrients. 2026;18(14):2251. https://pubmed.ncbi.nlm.nih.gov/42514320/
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