NMN is a naturally occurring form of Vitamin B3 that is studied for slowing aging and for preventing diseases of aging. Dietary NMN is converted to nicotinamide adenine dinucleotide (NAD+), a coenzyme in all living cells which is required for numerous biological processes. NAD+ levels naturally decline with age, reaching less than 50% of youthful levels by middle age.^[3] Decreased NAD+ levels have been attributed to increased inflammation and oxidative stress as well as to the development of age-related conditions such as hypertension, cognitive decline, and type 2 diabetes. While the anti-aging effects of NMN in rodents are well-established, studies are ongoing to determine whether equally impressive anti-aging effects are possible in humans.

NMN is taken as a supplement to increase levels of the coenzyme NAD+. It is unknown whether NMN will have the same therapeutic effects in humans as seen in rodent models, but emerging evidence is promising.^[4][5]

So far, most randomized controlled trials in humans have focused on proving the safety of NMN supplements and their ability to increase blood NAD+ levels in different populations. Some clinical research has shown that NMN increases physical ability in aging populations,^[1] improves cardiovascular disease biomarkers such as arterial stiffness,^[6] and increases cellular NAD+/NADH levels.^[4] Although these results have been promising, additional large-scale trials are needed to better understand the benefits in humans.

The main drawback to NMN is a lack of long-term studies in humans. NMN has been shown to be safe in doses up to 1200 mg daily for 6 weeks and 900 mg daily for 8 weeks. Doses of 2000 mg daily have been taken for up to 14 days with no adverse effects.^[1] Long-term safety of chronic and/or higher doses of NMN hasn’t been tested.

It is also important to note that more research is needed to better-understand the effects of boosting NAD+ in certain contexts. For example, by elevating cellular NAD+ levels, NMN could potentially exacerbate chronic inflammation by increasing the release of pro-inflammatory cytokines from senescent cells.^[7] It is important to note, however, that NMN-induced inflammation has not been observed in human trials to date.

As a precursor to NAD+, NMN supplementation has the potential to restore NAD+ to youthful levels, thereby restoring the function of NAD+-dependent enzymes in the body. After NMN is taken, it is absorbed into the bloodstream and rapidly converted to NAD+,^[8] which is an important cofactor for many biological processes, including immune response, DNA repair, cell division, mitochondrial function, epigenetics, and redox reactions.^[9] As NAD+ levels naturally decrease with age, the activity of enzymes dependent on NAD+ for their function also decreases.^[10] Since reduced activity of NAD+-consuming enzymes (e.g. sirtuin 1) has been linked to the aging process, restoring NAD+ levels to more youthful levels is theorized to slow down the aging process.^{[11] [12]}

NMN is currently in legal limbo in the U.S., and most retailers have pulled NMN products from their shelves.

The path from NMN being legal for sale as a dietary supplement to effectively banned for supplement sales has several twists and turns. In 2018, NMN was granted GRAS (Generally Regarded As Safe) status by an FDA panel in 2018, which made it legal for use as a food additive. GRAS designation doesn’t apply to supplements, however—only food or food additives. For a product to be marketed and sold as a supplement, manufacturers need to submit a notification of a “New Dietary Ingredient” (NDI) to the FDA, before bringing the product to the market. NDI's contain information providing the basis for concluding that the supplement is reasonably safe and, if approved by the FDA, pave the way for sales and marketing as a supplement.

One company did successfully get an NDI approved by the FDA for NMN supplements in 2022, which gave NMN the appropriate legal status for supplement sales. However, later the same year, the FDA changed their stance on NMN’s status as a dietary supplement. Several companies that were testing NMN in clinical trials successfully lobbied the FDA to have NMN classified as an investigational drug. This effectively made NMN supplement sales illegal according to 21 U.S.C. § 321(ff) (section 201(ff) of the Federal Food, Drug, and Cosmetic Act, which prevents the sales or marketing of agents classified as investigational drugs.
This prompted the FDA to revoke the NDI, which effectively banned the sales and marketing of NMN supplements in the US. Technically, selling NMN as a food additive is still legal, since NMN’s GRAS status was not affected by the withdrawal of the NDI. Nonetheless, most retailers stopped selling NMN products considering its uncertain legal status.