NAD⁺ shows up on men’s-health menus next to testosterone, ED medication and hair-loss scripts, and the placement does the arguing. Nothing on the page has to claim a hormonal effect; sitting on that shelf implies one.
So we went looking for the male-specific evidence. There is some. It is not the part being sold.
What we searched for, and did not find
On September 13, 2026 we ran four searches against PubMed. A search for nicotinamide riboside testosterone men returned zero results. A search for nicotinamide mononucleotide erectile dysfunction returned zero results. A search for NAD+ precursor male fertility sperm clinical trial returned zero results. A search for NAD+ supplementation sex differences humans returned two records, neither of which compares men and women taking a NAD⁺ precursor — one is an exercise trial in Friedreich’s ataxia, the other a laboratory study of corneal dystrophy.
No published trial has measured what a NAD⁺ precursor does to testosterone, erectile function, or sperm. Those are the three things the shelf placement implies, and they are the three with nothing behind them at all. If you want the general picture first, what NAD⁺ is and what raising it has been shown to do is the place to start.
The trials that did enroll only men
Three exist, and they are worth knowing about, because they are among the cleanest results in this field and they mostly point the same way.
Insulin sensitivity. A randomized, double-blind, placebo-controlled trial gave 40 sedentary men with a BMI above 30, aged 40 to 70 (n = 40), nicotinamide riboside at 1,000 mg twice daily or placebo for 12 weeks, and measured insulin sensitivity with a hyperinsulinemic-euglycemic clamp — the reference method, not a proxy. Insulin sensitivity, endogenous glucose production, glucose disposal and glucose oxidation were not improved. Nor were resting energy expenditure, lipolysis, lipid oxidation or body composition [1].
Muscle mitochondria. The same 40 men gave muscle biopsies. Respiratory capacity, mitochondrial content, fractional area and network morphology were all unaffected by NR. Steady-state NAD⁺ levels in skeletal muscle did not change either; the one protein that moved was NAMPT, which fell by 14% [2]. That is a trial designed to catch a mitochondrial effect, in the tissue where the effect was supposed to be, finding none.
Aerobic capacity. A six-week randomized, double-blind trial in 48 amateur runners — ten men and two women in each of four arms, so 40 of the 48 participants were male — compared placebo with NMN at 300, 600 or 1,200 mg a day alongside training. Oxygen uptake, percentage of maximum oxygen uptake, and power at the first and second ventilatory thresholds rose more in the medium and high dose groups than in the control group. But VO₂max itself did not differ, and neither did O₂-pulse, oxygen uptake relative to work rate, or peak power [3]. A real signal, on some measures and not the headline one, in people who were already training five to six times a week.
Safety and metabolism. A small single-arm study gave single oral doses of 100, 250 and 500 mg of NMN to ten healthy Japanese men and tracked them for five hours. No significant clinical symptoms, no meaningful changes in vital signs, and a dose-dependent rise in NMN metabolites. Sleep quality score showed no difference before and after [4].
The one place a real sex difference has been measured
It is not in a supplement trial. It is in tissue.
Researchers analyzed pelvic skin samples from 49 people aged from newborn to 77 (n = 49) and measured DNA damage, PARP activity, SIRT1 activity and tissue NAD⁺ against age. NAD⁺ fell with age in both sexes, and more steeply in men: p = 0.001, r = −0.706 in males against p = 0.01, r = −0.537 in females. PARP activity rose sharply with age in males (p < 0.0001, r = 0.768) and inversely tracked tissue NAD⁺; the authors report these associations as “less evident in females”. SIRT1 activity fell with age in males (p = 0.007) but not in females[5].
That is the strongest sex-specific finding in the human NAD⁺ literature, and it is worth being exact about what it is: a cross-sectional correlation in skin biopsies, showing that the decline differs by sex. It says nothing about whether supplementing changes anything, in either sex. Nobody has run that study.
The comparison you will see made, and why it does not hold
Somebody will eventually point out that the clearest positive metabolic result in this field came from a trial that enrolled only women, while the clearest null results came from trials that enrolled only men, and conclude that NAD⁺ works better in women.
The contrast is real. The conclusion is not available. The men-only trials used nicotinamide riboside at 2,000 mg a day in obese, insulin-resistant middle-aged men; the women-only trial used nicotinamide mononucleotide in postmenopausal women with prediabetes. Different molecule, different dose, different population, different duration — and NR and NMN are not interchangeable. Any one of those differences could account for the gap. Sex is simply the one that is easiest to notice.
The Danish investigators made the point themselves at the end of their muscle paper: future studies of NR in human skeletal muscle “may include both sexes” [2]. Our search for sex differences in human NAD⁺ supplementation, run the same day as the other three, returned two records and neither is that study.
So what should a man actually take from this?
That the male-specific case for NAD⁺ is weaker than the general case, and the general case is already modest. A 2026 systematic review of 113 studies found that oral NR and NMN consistently raise the biochemical marker and are generally well tolerated, while their effects on functional, metabolic and vascular outcomes were “heterogeneous and often null or endpoint-specific” [6]. Two of the null results in that pile are the men-only trials above.
If you still want to try it, the format with the evidence is also the cheap one: an oral precursor, at roughly a tenth of what an injection subscription costs — our cost calculator does that comparison per milligram. What we would ask you not to do is buy it as a testosterone adjacent product. Nothing has been measured there, and a men’s-health page that implies otherwise is charging you for the implication.