NMN and NR Dosing: Evidence-Based Protocols for NAD+ Precursors, Rapamycin, and Metformin

Why NAD+ Levels Matter for Aging

NAD+ is the electron carrier at the center of mitochondrial metabolism, sirtuin activity, and DNA repair. In a 2013 mouse study published in Cell, Gomes et al. showed that declining NAD+ in aged mouse muscle triggered a pseudohypoxic state and mitochondrial dysfunction that was partially reversed by NMN supplementation [1]. This is mouse tissue data, not a human measurement.

Human data on the exact magnitude of age-related NAD+ decline are less complete than marketing materials often suggest. The widely repeated estimate that whole-blood or muscle NAD+ falls by roughly half between the 40s and 60s traces back largely to mouse studies and small human cohorts rather than a single definitive human dataset, and the precise figure should be treated as an approximation pending direct verification in the primary literature.

Sirtuins, particularly SIRT1 and SIRT3, require NAD+ as a co-substrate. Lower NAD+ is mechanistically linked to blunted sirtuin activity, reduced FOXO signaling, and increased NF-kB inflammatory activity; a 2018 review by Rajman, Chwalek, and Sinclair in Cell Metabolism catalogs this evidence [3].

Two classes of oral supplements reliably raise NAD+ measures in humans: NMN (nicotinamide mononucleotide) and NR (nicotinamide riboside). Both are NAD+ precursors that converge on the same NAD+ salvage pathway inside cells. Clinicians discussing these with patients also often bring up two prescription compounds used off-label for longevity: rapamycin (sirolimus), an mTOR inhibitor, and metformin, an AMPK activator. All four are covered below with the dose ranges and trial data behind them.

NMN Dosing: Human Trial Data

NMN is proposed to enter cells via the Slc12a8 transporter and be phosphorylated directly to NAD+. The most widely cited human pharmacokinetic study is Irie et al. (2020), a double-blind, placebo-controlled crossover in 10 healthy men. A single oral 100 mg, 250 mg, or 500 mg dose raised plasma NMN and downstream metabolites in a dose-dependent manner within 30 minutes; no adverse events were recorded at any dose [4]. This is a single small trial and has not been replicated at scale.

The most informative efficacy trial to date is Yoshino et al. (2021), published in Science. In 25 postmenopausal women with prediabetes, 250 mg/day NMN for 10 weeks improved muscle insulin signaling and upregulated gene expression of SIRT1 and PGC-1-alpha compared to placebo [5]. Body weight and fasting glucose did not change significantly, which is a reminder that NAD+ restoration did not act as a general metabolic fix in this trial.

At higher doses, Liao et al. (2021) reported a randomized, double-blind trial in 66 recreational runners comparing 300 mg/day NMN, 600 mg/day NMN, and placebo over six weeks. The 600 mg/day group showed a larger increase in aerobic capacity than placebo [6]. This is one trial in a specific athletic population; whether the effect generalizes to non-athletes or older adults has not been tested.

Typical dosing range in practice: 500 to 1,000 mg/day, often split into two doses in the morning and early afternoon to align with circadian NAD+ patterns. Some longevity-focused clinicians go higher, though no published human trial has run above roughly 1,200 mg/day for a sustained period with safety as a primary endpoint, so doses above the studied range carry an unknown safety margin.

Sublingual and liposomal NMN formulations are marketed as higher-bioavailability alternatives. That claim rests largely on the Irie 2020 finding that a 100 mg sublingual dose raised plasma NMN within 30 minutes. A head-to-head bioavailability comparison of sublingual versus oral NMN has not been published as of this writing, so superiority claims for sublingual products go beyond the available evidence.

NR Dosing: Human Trial Data

NR is transported into cells via nucleoside transporters and converted to NMN before entering the NAD+ pool. The key single-dose pharmacokinetic paper is Trammell et al. (2016) in Nature Communications: a randomized crossover study in 12 healthy adults found that a single 1,000 mg NR dose raised whole-blood NAD+ roughly 2.7-fold within 8 hours of baseline, with a 250 mg dose producing an increase of roughly 40 to 60% [7].

Martens et al. (2018) in Nature Communications (24 middle-aged and older adults) found that NR at 500 mg twice daily for six weeks raised whole-blood NAD+ by roughly 60% and reduced some circulating inflammatory markers, including IL-6, though the study was not powered to detect clinical outcomes [8].

In healthy older men, Elhassan et al. (2019) in Cell Reports reported that NR at 1,000 mg/day for 21 days raised skeletal-muscle NAD+ measures and shifted sirtuin-related gene expression in muscle biopsies [9]. The exact percentage increase varies by tissue compartment in the paper and should be checked against the primary source before quoting a single number.

Typical dosing range in practice: 250 to 1,000 mg/day, usually starting at 500 mg/day and escalating based on tolerability. Mild flushing, nausea, and GI upset were the most common side effects reported in the Martens 2018 trial at the 1,000 mg/day dose.

NR is generally priced lower per milligram than NMN. No published head-to-head RCT has compared clinical outcomes between the two compounds directly.

NMN vs. NR: Which Should Patients Choose?

Both compounds raise NAD+ measures in human trials. The choice mostly comes down to cost, tolerability, and which trial population most resembles the patient, rather than a trial showing one is clinically superior.

Patients who experience flushing on NR may tolerate NMN better, and vice versa. Both are usually taken earlier in the day; animal data from Peek et al. (2013) suggest NAD+ and SIRT1 activity follow a circadian pattern in mice, and evening dosing is generally avoided on that basis, though this reasoning has not been directly tested with NMN or NR dosing time in humans [10].

Rapamycin Weekly Dosing for Longevity

Rapamycin is the drug with the strongest animal lifespan-extension data of anything discussed here. Harrison et al. (2009) in Nature showed rapamycin feeding starting at 600 days of age (roughly equivalent to a 60-year-old human) extended median lifespan in genetically heterogeneous mice, with a larger effect in males than females in that cohort [11]. Later work from the NIA Interventions Testing Program has reported further gains from rapamycin started at different ages and doses, including effects at the upper end of the survival distribution; exact percentage figures differ across these papers by cohort and dose, and any specific number should be checked against the primary ITP publication rather than repeated as a fixed value.

Rapamycin inhibits mTORC1, reducing protein synthesis, promoting autophagy, and shifting cells toward a maintenance state. Chronic daily dosing in humans is used at immunosuppressive levels (roughly 2 to 5 mg/day) after organ transplant, and carries real risks: impaired wound healing, hyperlipidemia, glucose intolerance, and infection susceptibility. Those risks are the reason longevity researchers and clinicians moved toward intermittent, once-weekly dosing rather than daily dosing.

The weekly dosing rationale: pharmacokinetic modeling suggests a single weekly dose can inhibit mTORC1 enough to trigger autophagy while allowing mTORC2 and immune function to recover before the next dose. Investigators involved in the Dog Aging Project have studied intermittent, weekly rapamycin in companion dogs, including cardiac and safety monitoring, and have described the early signals as encouraging. The specific dose, duration, and effect size sometimes quoted for this work need direct verification against the primary trial report before being treated as an established finding, since the review article cited here is a translational overview of the broader Dog Aging Project rather than the original trial publication [12].

Off-label longevity protocols in clinical practice: most longevity physicians prescribing rapamycin off-label use 5 to 10 mg orally once weekly, with some starting at 2 to 3 mg/week and escalating over 4 to 6 weeks. Monitoring commonly includes a lipid panel, CBC, and fasting glucose roughly every 3 months. Mouth sores (oral ulcers) are a commonly reported side effect at higher weekly doses in case series; exact incidence figures vary and should be confirmed with the prescribing clinician rather than treated as fixed. Taking rapamycin with a high-fat meal delays and reduces peak drug concentration, which is why most protocols specify fasted dosing; the precise percentage change in peak concentration depends on the formulation and should be checked against product-specific pharmacokinetic data rather than quoted as a universal figure. An alternative "pulsed" protocol described by Blagosklonny (2019) in Aging proposes 6 to 7 mg once weekly or biweekly, with drug holidays every 3 to 4 months to reassess immune tolerance [13].

No completed Phase 3 longevity RCT exists for rapamycin in healthy humans. The PEARL trial (rapamycin versus placebo in healthy adults aged 50 to 85) at the University of Washington is ongoing and collecting biological-age biomarker data. Informed-consent discussions must be explicit that this is off-label use in a population where the long-term risk-benefit profile has not been established by a completed trial.

Off-Label Metformin Dosing for Longevity

Metformin is a biguanide FDA-approved since 1994 for type 2 diabetes. Its mechanism relevant to aging research is AMPK activation, which mimics some effects of caloric restriction and suppresses hepatic mTORC1 activity; proposed secondary mechanisms include reduced mitochondrial complex I activity and lower circulating IGF-1 [14].

The observational signal that drove longevity interest in metformin comes from Bannister et al. (2014) in Diabetes, Obesity and Metabolism: in a UK cohort of over 78,000 people with type 2 diabetes on metformin, all-cause mortality was reported as lower than in matched non-diabetic controls not on metformin, a counterintuitive finding that suggested a benefit beyond glucose control [15]. This is an observational, not randomized, comparison, and residual confounding (for example, healthier patients being more likely to be prescribed and to stay on metformin) cannot be ruled out.

The TAME (Targeting Aging with Metformin) trial, registered as NCT03077360 and funded by the American Federation for Aging Research, is the trial designed to test this directly. TAME plans to enroll 3,000 adults aged 65 to 79 without diabetes across academic centers, dosing at 1,500 mg/day extended-release metformin versus placebo, with a primary composite endpoint of incident cardiovascular disease, cancer, dementia, or death over 6 years. As of this writing the trial has not reported primary results.

Off-label dosing protocol used in practice: many longevity clinicians mirror the TAME dose: 500 mg extended-release with dinner for 2 weeks, then 1,000 mg extended-release with dinner for 2 weeks, then a maintenance dose around 1,500 mg/day (for example 500 mg with breakfast and 1,000 mg with dinner). Some clinicians target up to roughly 1,700 mg/day. Extended-release formulations are generally better tolerated than immediate-release; gastrointestinal side effects such as nausea and diarrhea are common with immediate-release metformin, though exact incidence figures vary across studies and should be checked against current prescribing information rather than treated as fixed.

A caution worth discussing with patients concerns exercise timing. A small randomized trial has reported that metformin may blunt the expected gains in muscle hypertrophy and strength when combined with progressive resistance exercise training in older adults, compared with exercise plus placebo. This trial looked at resistance training and muscle size and strength endpoints, not aerobic capacity (VO2 max); whether metformin also blunts adaptations to aerobic training is a separate question this trial does not answer directly, and any aerobic-specific claim should be verified against a study of aerobic exercise before being treated as established. Because of the resistance-training finding, some longevity physicians time metformin dosing away from resistance workouts, particularly for patients prioritizing strength and lean mass.

Vitamin B12 depletion is a well-established adverse effect, since metformin reduces ileal B12 absorption. Annual B12 monitoring is recommended by the American Diabetes Association Standards of Care https://diabetesjournals.org/care/issue/47/Supplement_1 [17], and supplementation with 500 to 1,000 mcg methylcobalamin daily is commonly co-prescribed in longevity protocols using metformin.

Combining NMN/NR, Rapamycin, and Metformin

A subset of longevity-focused clinicians combine these compounds, but published human safety data on the combination is minimal. Metformin activates AMPK and inhibits mTORC1 through a different upstream pathway than rapamycin's direct mTORC1 binding, so combining them could plausibly produce additive mTOR suppression, though this has not been directly studied in a combination trial. NMN or NR supplements NAD+ pools that metformin's complex-I inhibition may partially deplete, which is a theoretical rationale for pairing them rather than a demonstrated clinical benefit.

The concern with stacking is over-suppression of mTOR, which is not purely catabolic; it also supports muscle protein synthesis. Patients combining rapamycin, metformin, and exercise should be monitored for sarcopenia progression, for example with periodic lean-mass and grip-strength checks.

There is no published expert consensus statement specifically endorsing combined NMN/NR, rapamycin, and metformin protocols. Kennedy and Lamming's mTOR biology review is a foundational reference for why combining an mTOR inhibitor with other interventions warrants caution [18], but it is a general mechanistic review rather than a combination-protocol guideline. The practice pattern described here reflects common off-label clinical practice, not a formal consensus, and should be individualized with the prescribing clinician.

Monitoring and Lab Testing Recommendations

Clinician Discussion and Monitoring Framework

This guide provides a structure for discussing longevity interventions with your doctor, distinguishing between FDA-approved uses, off-label applications, supplements, and areas requiring clinical judgment. It is not a substitute for personalized medical advice and does not take the place of your clinician's evaluation of your medical history, test results, and current medications.

Two points define the outer edge of this table. First, none of these regimens has a completed trial showing it extends human lifespan or delays a specific disease; the doses above come from mechanistic, pharmacokinetic, or short-duration trials, not from long-term outcome data. Second, any specific starting dose, escalation schedule, or lab cutoff should be set by the prescribing clinician for the individual patient, not read off this table as a fixed instruction.