NAD Precursors Class Overview Monograph

What counts as an NAD precursor?

NAD+ is a coenzyme for redox reactions and a cosubstrate for NAD+-consuming enzymes, including sirtuins, poly-ADP-ribose polymerases (PARPs) and CD38/CD157 ectoenzymes [14]. Baseline NAD+ needs can be met from dietary tryptophan or from less than 20 mg of daily niacin, which covers nicotinic acid and/or nicotinamide [4]. NR and NMN are precursors that cells convert to NAD+ [15].

The case for supplementing them comes largely from animals: in rodents, obesity and aging impair NAD+ synthesis and NMN availability is a rate-limiting step [15]. NAD+ concentrations change with age, and in animal models restoring NAD+ improves age-related defects [16][14]. Those findings are the rationale for human trials, not the result of them.

Do NMN and NR raise NAD+ in humans?

In blood, yes, consistently and within weeks.

• NMN 250 mg/day for 12 weeks raised whole-blood NAD+ in 30 healthy adults, with no abnormalities on physiological or laboratory testing [5].
• In 80 middle-aged adults given 300, 600 or 900 mg/day for 60 days, blood NAD rose in every NMN group (p <= 0.001 versus placebo and baseline) and was highest at 600 and 900 mg [6].
• NR 1,000 mg/day for 6 weeks raised PBMC NAD+ about 60% above placebo in the 24 adults aged 55 to 79 who completed a crossover trial [7].
• In an 8-week dose-ranging trial in overweight adults, 100, 300 and 1,000 mg/day of NR raised whole-blood NAD+ by 22%, 51% and 142% respectively [17].
• NR 1,500 mg twice daily for 4 weeks raised blood NAD+ up to 5-fold in a 20-person Parkinson's disease trial (10 on NR) [11], and 1,000 mg/day for 30 days produced a significant but variable rise in brain NAD measured by magnetic resonance spectroscopy in 30 newly diagnosed Parkinson's patients [18].

Does a higher blood NAD+ level produce a benefit?

Not reliably. The strongest signal is metabolic, and it comes from one small trial. In 25 postmenopausal women with prediabetes who were overweight or obese, insulin-stimulated glucose disposal rose 25 plus or minus 7% with NMN 250 mg/day over 10 weeks and did not change with placebo; 25 women completed (13 NMN, 12 placebo), and there was no group-by-time difference in weight or HbA1c (interaction p = 0.396) [15].

Other results are flat or mixed:

• In 12 men aged 70 to 80, NR 1 g/day for 21 days did not raise muscle NAD+ (210 vs 197 pmol/mg, p = 0.22), although NAAD, a marker of NAD+ synthesis, doubled. Mitochondrial respiration, grip strength, insulin sensitivity and muscle blood flow were unchanged [19].
• NR 1,000 mg twice daily for 12 weeks in 40 sedentary obese men improved neither insulin sensitivity measured by clamp nor energy expenditure, lipolysis or body composition [10].
• NMN 250 mg/day for 6 or 12 weeks in older men produced only nominally significant improvements in gait speed and left grip, which the authors said needed confirmation in larger studies, and no body composition effect [20].
• In 108 older Japanese adults, afternoon NMN gave the largest effect on the five-times sit-to-stand test (d = 0.72) and on drowsiness (d = 0.64), but all groups, including placebo, improved on the sit-to-stand test [21]. In the 80-person dose-ranging trial, six-minute walk distance was greater than placebo in all NMN groups [6].

Pooled analyses are less encouraging than individual trials. A 2025 systematic review and meta-analysis of randomized trials in older adults found NMN had no significant effect on skeletal muscle index, handgrip strength, gait speed or the five-times chair stand test [2]. A second 2025 meta-analysis of 12 trials with 513 participants found NMN raised blood NAD but most clinical outcomes, including fasting glucose, triglycerides and cholesterol, did not differ significantly from control; risk of bias had some concerns in 7 trials and was high in 5 [3].

What doses were studied?

These are research doses, not recommended intakes:

• NMN 250 mg/day for 10 to 12 weeks [15][5][20]
• NMN 300, 600 or 900 mg/day for 60 days [6]
• NMN 1,250 mg once daily for up to 4 weeks [9]
• NR 1,000 mg/day for 3 to 6 weeks [7][19]
• NR 1,000 mg twice daily (2,000 mg/day) for 12 weeks [10]
• NR 1,500 mg twice daily (3,000 mg/day) for 4 weeks [11]

Regulatory status of NMN and NR

NR and NMN are sold in the US as oral dietary supplements, and neither is an FDA-approved drug. No NAD+ precursor product is approved by FDA to treat aging or any disease [1].

For NR, FDA responded to ChromaDex's GRAS notice GRN 000635 with a no-questions letter dated August 3, 2016, and stated that it had not made its own GRAS determination [8].

NMN is not banned. In its response to a citizen petition in docket FDA-2023-P-0872, posted September 29, 2025, FDA concluded that NMN is not excluded from the dietary supplement definition, because it found evidence NMN was marketed as a US supplement before it was authorized for drug investigation [1][22]. NMN remains a new dietary ingredient, so a maker must file an NDI notification, or rely on a prior notification covering that supplier's ingredient, before selling it [1].

What the trials reported for safety

NMN: 1,250 mg once daily for up to 4 weeks in 31 healthy adults aged 20 to 65 produced no severe adverse events and no changes beyond physiological variation in anthropometry, hematology, biochemistry, urine or body composition [9]. NMN 250 mg/day for 12 weeks in 30 adults caused no abnormalities on physiological or laboratory tests and no obvious adverse effects [5]. NMN 300 to 900 mg/day for 60 days in 80 adults raised no safety issues on adverse-event, laboratory and clinical monitoring [6].

NR: in a 6-week crossover trial of 30 randomized adults aged 55 to 79, 7 participants reported 14 mild adverse events, including nausea, flushing, leg cramps and bruising, with no serious events [7]. NR 2,000 mg/day for 12 weeks in 40 obese men produced no serious adverse events and normal safety blood tests [10], and 3,000 mg/day for 4 weeks in that 20-person Parkinson's disease trial produced no moderate or severe adverse events [11]. In a 21-day crossover of 12 men aged 70 to 80, 4 men (33%) self-reported increased libido on NR and none on placebo, with no clinical adverse events [19].

Human safety data beyond about 12 weeks are lacking, and trials were short and small (n = 12 to 140) [12]. Cancer risk with chronic NAD+ boosting is a theoretical concern; no human data were identified [12]. People who are pregnant or breastfeeding, children, and people with cancer or kidney or liver disease were not studied in these trials, so safety in those groups is unknown [12].

Drug interactions

A 2023 review of NAD+-boosting supplements in humans identified no drug-interaction studies of NMN or NR, whether for CYP enzymes, drug transporters or pharmacodynamic effects [12]. Neither safety with a specific prescription drug nor an interaction with one has been established.

One clinical confound is documented. In the NR-SAFE trial (20 people with Parkinson's disease, 10 on NR), an apparent improvement in MDS-UPDRS scores was also associated with a shorter interval since the last levodopa dose, so the clinical result was confounded [11]. NR recipients had a slight initial rise in serum homocysteine, and the authors judged the methyl donor pool to be intact [11].

Injectable NAD+

Injectable or IV NAD+ is a compounded product, not an FDA-approved drug [13]. No NAD+ product is approved by FDA to treat aging, fatigue or any disease [1]. For the injectable form, see NAD+ injection.