NMNWhat the studies show
The direct precursor to NAD+, which raised muscle insulin sensitivity by about 25% in prediabetic women over ten weeks and changed little else.
5 min read · Small human studies · Updated November 2026
In short
- Name
- nicotinamide mononucleotide
- Evidence
- Small human studies
- Bottom line
- Small randomised, placebo-controlled trials in people lasting 10 to 12 weeks, which agree that NMN raises blood NAD+ and disagree, or stay silent, on whether that changes anything a person would notice.
Before you read this
This guide explains what published studies found. That is all it is.
It is not medical advice and it is not instructions for using anything. Where a dose appears, we are reporting what a named study gave the people or animals in it — a fact about the study, not an instruction to you.
The compounds here are not approved by the FDA for use in people and are sold for laboratory research only. A study tells you what happened to the subjects in it; it does not tell you what would happen to you. Talk to a doctor first.
What it is
Nicotinamide mononucleotide, NMN, is the molecule one step before NAD+ on the main route cells use to make it. Cells convert nicotinamide — vitamin B3 — into NMN with an enzyme called NAMPT, then NMN into NAD+ with the NMNAT enzymes; the first of those steps is the slow one, which is the argument for supplying NMN directly 1. It is not a peptide; it is a nucleotide, a chemical cousin of the building blocks of RNA, and it occurs in small amounts in foods such as edamame, broccoli and avocado. Interest in it grew out of Shin-ichiro Imai's laboratory at Washington University in St. Louis, which showed in a 2016 study that a year of NMN in drinking water slowed several measures of ageing in mice — weight gain, falling energy expenditure, declining insulin sensitivity and eye function among them 1.
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Does it raise NAD+ in people?
Yes, and that is the best-established thing about it. The first human study, published in 2020 by a Keio University group, gave ten healthy men single doses of 100, 250 or 500 mg of NMN and found the nicotinamide metabolites in their blood rose in proportion, with no change in heart rate, blood pressure, liver or kidney tests over the following hours 2. Later trials with daily dosing for weeks found the same: blood NAD+ and its related metabolites rose and stayed up for as long as the supplement was taken 3. What is harder to show is whether that reaches the tissues that matter — muscle, liver, brain — rather than just the blood.
The 2021 Science trial in prediabetic women
The most rigorous trial is from Washington University, published in Science in 2021. Twenty-five postmenopausal women with prediabetes and overweight or obesity were randomised to 250 mg of NMN or placebo daily for ten weeks, and their insulin sensitivity was measured with a clamp — the gold-standard method, in which insulin is infused and glucose uptake is measured directly 4. Muscle insulin sensitivity rose by about 25% in the NMN group and did not change on placebo; muscle biopsies showed more activity in the genes that respond to insulin and remodel muscle 4. Everything else stayed put: body weight, body fat, liver fat, blood pressure, cholesterol, blood sugar during a glucose test and liver insulin sensitivity were all unchanged 4. It is a real result, measured carefully, in a small and specific group, and the authors themselves called for larger trials before drawing clinical conclusions.
The Tokyo trial in older men
A University of Tokyo trial published in 2022 took 42 healthy men aged 65 and over and gave them 250 mg of NMN or placebo daily for 12 weeks 3. Blood NAD+ and related metabolites rose on NMN. On the physical tests the NMN group improved on some measures — gait speed and grip strength in the left hand — and not on others, and the differences were modest; the authors described the muscle findings as preliminary 3. A 60-day trial in 80 middle-aged adults published in 2023 compared 300, 600 and 900 mg a day with placebo, found blood NAD+ rose with the dose, and reported that participants on the two higher doses walked farther in a six-minute walk test than those on placebo 5.
What is not known
No trial has followed NMN for longer than a few months, so nothing is known about years of it. No trial has measured an outcome that matters on its own terms — a disease prevented, a function preserved into old age. The mouse results that drive the interest, the 2016 study above among them, have not been shown in people 1. NMN is not an approved drug anywhere; it is sold as a supplement in Japan and elsewhere, and in the United States its status as a supplement ingredient has been disputed by the FDA because the molecule was also under study as a drug.
What these studies are, and aren't
Small human studies. Small randomised, placebo-controlled trials in people lasting 10 to 12 weeks, which agree that NMN raises blood NAD+ and disagree, or stay silent, on whether that changes anything a person would notice.
Sources
- 1Mills KF et al. Long-Term Administration of Nicotinamide Mononucleotide Mitigates Age-Associated Physiological Decline in Mice. Cell Metabolism, 2016.
- 2Irie J et al. Effect of oral administration of nicotinamide mononucleotide on clinical parameters and nicotinamide metabolite levels in healthy Japanese men. Endocrine Journal, 2020.
- 3Igarashi M et al. Chronic nicotinamide mononucleotide supplementation elevates blood nicotinamide adenine dinucleotide levels and alters muscle function in healthy older men. npj Aging, 2022.
- 4Yoshino M et al. Nicotinamide mononucleotide increases muscle insulin sensitivity in prediabetic women. Science, 2021.
- 5Yi L et al. The efficacy and safety of β-nicotinamide mononucleotide (NMN) supplementation in healthy middle-aged adults: a randomized, multicenter, double-blind, placebo-controlled, parallel-group, dose-dependent clinical trial. GeroScience, 2023.
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