NAD+ is a coenzyme that cells use in energy metabolism, and its availability falls with age in animals and in people. The idea behind NMN and nicotinamide riboside (NR) is that a precursor taken by mouth raises NAD+. Animal studies support that idea. In people, the evidence is four small controlled trials of oral precursors, plus one pilot of IV NAD+ that measured blood levels only.
Nicotinamide riboside in healthy adults
Martens and colleagues gave 30 healthy adults aged 55 to 79 nicotinamide riboside, 500 mg twice a day, and placebo, for six weeks each in a crossover order. NAD+ in blood cells was about 60% higher on riboside than on placebo. Riboside was well tolerated. The side effects reported were mild, such as nausea, flushing and leg cramps. The trial was designed to show that NAD+ rises and that the dose is tolerated, not to measure health outcomes.
NMN in prediabetic women
Yoshino and colleagues ran a 10-week randomized, double-blind, placebo-controlled trial in 25 postmenopausal women with prediabetes who were overweight or obese. Twelve took placebo and 13 took 250 mg of NMN a day. Insulin-stimulated glucose disposal, measured with a clamp, rose after NMN and did not change after placebo, and insulin signalling in muscle followed the same pattern. Blood glucose, blood pressure, body composition and liver fat did not change in either group.
NMN in healthy older men
Igarashi and colleagues randomized 42 healthy older men to 250 mg of NMN a day or placebo for six or twelve weeks. Whole-blood NAD+ and related metabolites rose on NMN. Gait speed and left-hand grip showed nominal improvements, which the authors say need confirming in larger studies. Body composition did not change.
A null trial in men with obesity
Dollerup and colleagues gave 40 men with obesity and insulin resistance 1,000 mg of nicotinamide riboside twice a day, or placebo, for 12 weeks. Insulin sensitivity, glucose production and body composition did not improve. Animal studies had suggested that riboside might improve insulin sensitivity; this human trial did not show it.
IV NAD+: one pilot, not a treatment study
Grant and colleagues gave eleven men a six-hour IV infusion of NAD+ at about 2 mg a minute: eight received NAD+ and three were controls. Plasma NAD+ showed no change until after two hours, and NAD+ and methylnicotinamide appeared in urine by six hours. The study followed where the infused NAD+ went. It measured no health outcome.
Muscle and older adults
A 2025 systematic review and meta-analysis of randomized trials of NMN and riboside in older adults found no support for preserving muscle mass or function. Its authors call for work on dose, on people with low baseline NAD+, and on combined treatments.
What this does not say
- These trials used oral precursors, not injected NAD+. They do not show that IV NAD+ does anything.
- Each trial was small (25 to 42 people) and short (6 to 12 weeks, or 10 weeks for the NMN trial in women).
- NAD+ in blood cells and whole blood are markers. A rise in them is not proof of a benefit for the heart, the brain or muscle.
- The trials did not test long-term safety or repeated dosing over years.
- The results do not agree: the riboside trial in men with obesity found no change in insulin sensitivity.
How we use this
The NAD+ product on this site is injected. The human trials above used oral precursors, and the one IV study is a metabolism pilot. Our physicians say that plainly when they discuss it with you. We do not promise that NAD+ will improve energy, muscle or insulin, and we do not present a rise in blood NAD+ as a result.
We use these trials to show what was measured, what was not, and how small the evidence is. Until a controlled trial with a health outcome exists for injected NAD+, we treat that route as unproven.
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- 1.Martens CR et al. Chronic nicotinamide riboside supplementation is well-tolerated and elevates NAD+ in healthy middle-aged and older adults. Nat Commun 2018. Nature Communications
- 2.Yoshino J et al. Nicotinamide mononucleotide increases muscle insulin sensitivity in prediabetic women. Science 2021. Science
- 3.Igarashi M et al. Chronic nicotinamide mononucleotide supplementation elevates blood nicotinamide adenine dinucleotide levels and alters muscle function in healthy older men. npj Aging 2022. npj Aging
- 4.Dollerup OL et al. A randomized placebo-controlled clinical trial of nicotinamide riboside in obese men: safety, insulin-sensitivity, and lipid-mobilizing effects. Am J Clin Nutr 2018. American Journal of Clinical Nutrition
- 5.Grant R et al. A pilot study investigating changes in the human plasma and urine NAD+ metabolome during a 6 hour intravenous infusion of NAD. Front Aging Neurosci 2019. Frontiers in Aging Neuroscience
- 6.Prokopidis K et al. The effect of nicotinamide mononucleotide and riboside on skeletal muscle mass and function: a systematic review and meta-analysis. J Cachexia Sarcopenia Muscle 2025. Journal of Cachexia, Sarcopenia and Muscle