NMN (Nicotinamide Mononucleotide)

NMN is a direct precursor to NAD+, the coenzyme that drops roughly 50% between young adulthood and old age and that drives sirtuin signaling, DNA repair, and mitochondrial function. Mouse studies from the Imai and Sinclair labs in the 2010s showed long-term oral NMN raised tissue NAD+, improved insulin sensitivity, and modestly improved physical function in aged animals. The human story is much narrower. As of 2026, only a handful of small RCTs have read out, the endpoints are mostly biomarkers rather than hard outcomes, and where functional outcomes were measured, the effects have been modest and inconsistent.

The strongest single human result is Yoshino 2021 in Science: 25 postmenopausal, overweight women with prediabetes took 250mg NMN or placebo for 10 weeks. Hyperinsulinemic-euglycemic clamp showed a significant increase in muscle insulin sensitivity in the NMN arm with no change in placebo. The effect was real but isolated to skeletal muscle; whole-body insulin sensitivity, HbA1c, and body composition did not move. It has not been independently replicated in a similar cohort. Igarashi 2022 in NPJ Aging gave 250mg/day for 12 weeks to older Japanese men (n=20 completers) and saw small, nominally significant improvements in gait speed and left-hand grip strength but not in body composition. Yi 2023 in GeroScience is the largest trial to date: 80 healthy middle-aged adults, dose-response across 300, 600, and 900mg for 60 days. NAD+ rose across all doses, six-minute walk distance improved across all dose groups versus placebo, and "blood biological age" (an algorithmic estimator) stayed flat while rising in placebo. The walk-distance effect is interesting but the trial is short and the biological-age endpoint is not a validated clinical outcome. Irie 2020 confirmed single oral doses up to 500mg are well-tolerated in healthy Japanese men.

The case for "feel-better" effects is weaker still. There are scattered open-label and small RCT reports of improved sleep quality, reduced fatigue, and better aerobic capacity in older adults (Liao 2021 in amateur runners is the most-cited), but the trials are small, often industry-funded, and the effects on subjective endpoints are not robust. Nothing in the human literature supports the longevity-extension claims that dominate the marketing.

The regulatory cloud that hung over NMN for three years has lifted. In late 2022 the FDA notified industry that NMN did not qualify as a dietary supplement under DSHEA because it had been authorized for investigation as a drug (by Metro International Biotech) before being marketed as a supplement, a position that pushed several major retailers to pull NMN products. After a Natural Products Association challenge, the FDA reversed course: in letters dated September 29, 2025 it concluded NMN is not excluded from the dietary-supplement definition, and on December 2, 2025 it issued a reinstatement letter confirming NMN's status as a lawful new dietary ingredient. As of 2026, NMN is again sold openly as a dietary supplement in the US and Amazon listings have largely returned, though pricing and brand availability are still normalizing after three years of disruption.

Practical bottom line: NMN reliably raises blood NAD+ at 250-900mg/day with good short-term safety. Downstream functional benefits in humans are modest, biomarker-heavy, and short-term. If you want to try it, 250-500mg/day matches the doses with the most human data, and you should accept that you are funding an open experiment rather than buying a proven intervention. The longevity story is still mostly a mouse story.