NMN and NR: what the NAD+ supplement trials actually found

NAD+ is a coenzyme every cell uses, and its levels fall with age. Nicotinamide mononucleotide (NMN) and nicotinamide riboside (NR) are precursors: you swallow them, your body converts them, blood NAD+ goes up. The pitch built on that biology is that restoring NAD+ restores something you can feel, usually framed as energy, muscle, or biological age.

The biology is real. The leap from the biology to the benefit is where the trials live, and the trials are not kind to the pitch.

Target engagement is not in doubt. In a randomized, placebo-controlled dose-ranging trial, whole-blood NAD+ rose 22 percent at 100 mg/day of NR, 51 percent at 300 mg, and 142 percent at 1,000 mg, and stayed up over eight weeks (Conze 2019, funded by ChromaDex, with two authors employed by the company). A 2026 head-to-head trial found NR and NMN raise circulating NAD+ comparably, while plain nicotinamide does not.

So the pills do the biochemical thing on the label. The question a buyer actually has is whether that translates, and it is a separate question with its own evidence.

This is the claim most often made to adults over 40, and it is the one with the cleanest answer. A 2025 systematic review and meta-analysis in the Journal of Cachexia, Sarcopenia and Muscle pooled the randomized trials of NMN and NR in adults with a mean age over 60. For NMN it found no effect on skeletal muscle index (mean difference -0.42, 95% CI -0.99 to 0.14), grip strength (left hand 0.61, -0.89 to 2.10; right hand 0.45, -1.06 to 1.96), gait speed (-0.01, -0.08 to 0.06) or five-times chair stand (-0.21, -0.70 to 0.29). Its conclusion is a single sentence worth reading twice: current evidence does not support NMN and NR supplementation for preserving muscle mass and function in adults with a mean age over 60.

The individual trials agree. A 24-week randomized trial in older men with diabetes and impaired physical performance, exactly the population the category targets, reported that NMN was safe but did not improve grip strength or walking speed. A 2024 trial whose title says NMN "maintained walking speed" reports in its own abstract that the primary outcome, a stepping test, showed no significant difference at either 4 or 12 weeks.

One meta-analysis dissents, reporting a small gait-speed effect. It draws on overlapping trials, reaches the opposite sign, and closes by calling NMN an encouraging anti-aging drug, which is not language a systematic review normally uses. Where two reviews of the same trials disagree this sharply, we weight the one with the tighter statistics and the more neutral framing, and we tell you the other exists.

The hyperinsulinemic-euglycemic clamp is the reference method for measuring insulin sensitivity, and three randomized trials have used it here. In obese men given 2,000 mg/day of NR for 12 weeks, insulin sensitivity, endogenous glucose production, glucose disposal and glucose oxidation were all unimproved. A crossover trial at 1,000 mg/day found no effect on insulin sensitivity, mitochondrial function, liver or muscle fat, blood pressure or inflammation, though fat-free mass rose slightly. A trial of pharmaceutical-grade NMN in overweight adults over 45 found no change in insulin sensitivity or liver fat.

The exception is the trial everyone cites: a 2021 Science paper reporting improved muscle insulin sensitivity in prediabetic women on 250 mg/day of NMN. It drew a published technical comment in the same journal pointing out that the NMN group started with 6.3 percent hepatic lipid and the placebo group with 14.8 percent (p=0.003), and concluding that this was not an effectively randomized trial. Both the comment and the authors' reply are in the record. A guide that cites the original without the comment is citing half of it.

Two 2024 to 2026 meta-analyses land in the same place: no significant benefit of NMN on fasting glucose, fasting insulin, HbA1c, HOMA-IR or lipid profile. One of them rated 5 of 12 trials at high risk of bias and wrote that an exaggeration of the benefits of NMN supplementation may exist in the field.

This is the part most articles, and most AI assistants, still have wrong, because the situation reversed recently and the old version is better indexed.

In October 2022 the FDA concluded that NMN was excluded from the dietary supplement definition, on the grounds that it had been authorized for investigation as a new drug before being marketed as a supplement. That is the fact everyone repeats.

On 29 September 2025, responding to a citizen petition from the Natural Products Association and the Alliance for Natural Health USA, the FDA reversed it. In the agency's own words: in light of FDA's revised interpretation of the race-to-market clause, we now conclude that NMN is not excluded from the definition of dietary supplement. The mechanism of the reversal is narrow and worth knowing: the FDA dropped its requirement that the earlier supplement marketing have been lawful, stating it will no longer evaluate whether the dietary supplement or food was lawfully marketed when making that determination. It noted evidence that NMN was marketed as a supplement in the United States as early as 2017. On 2 December 2025 it formally set aside the 2022 letters.

Two things that did not change. An accepted new-dietary-ingredient notification is a procedural step, not a safety approval, and the FDA says so in the same letters: acceptance does not constitute a finding that the ingredient is safe, and the agency is not precluded from acting later. And NR's status is separate and older: the FDA had no questions about ChromaDex's conclusion that NR is generally recognized as safe in 2016, while stating in the same letter that the agency has not made its own determination regarding the GRAS status.

Short-term tolerability is genuinely good. A 2026 meta-analysis pooling 15 NMN trials at 250 to 2,000 mg/day for 14 days to 24 weeks found no increase in overall, serious or withdrawal-related adverse events, and no liver-enzyme elevation. A 4-week trial pushed NR to 3,000 mg/day with no moderate or severe adverse events, though it did note a slight initial rise in serum homocysteine.

The honest caveat is duration, not toxicity. Almost nothing in this literature runs past six months, and there is no multi-year human safety data on either compound at supplement doses. There is also a gap between what was studied and what is sold: NR trials used 1,000 to 3,000 mg/day, while the European Food Safety Authority has assessed NR as safe in supplements up to 300 mg/day for healthy adults, and ChromaDex's own safety submission estimated an upper intake around 180 mg/day for a 60 kg adult.

Two signals are worth naming without inflating them. In a small crossover trial in untrained young men, blood-flow-restriction exercise raised muscle mitochondrial content 171 percent at 24 hours and that adaptation was abolished with NMN. It is 11 people and 7 days, so it is hypothesis-generating rather than conclusive, but it is the only human data on whether NMN interferes with training adaptation and the direction is unfavourable. Separately, a mouse study of triple-negative breast cancer reported increased cancer prevalence and brain metastases with NR supplementation. That is a rodent model with no human counterpart in either direction; it is a reasonable prompt to ask an oncologist first if you have active or prior cancer, and it is not evidence that NR causes cancer in people.

Prices below were read from each seller's own page on 2026-08-22, and the monthly figure is our arithmetic from the label's stated serving size, not a seller claim. NR at the mainstream brands runs about $40 to $116 a month: Tru Niagen 300 mg is $49.00 for 30 capsules and $40.67 a month equivalent at the 180-count size, Tru Niagen Pro 1,000 mg is $116.00 for a 30-day supply, and Elysium Basis is $65.00 for a stated 30-day supply. NMN runs roughly $30 to $120: ProHealth NMN 1000 is $39.95 for 30 servings, Toniiq NMN 1200 is $39.97, Wonderfeel Youngr is $88.00, and DoNotAge Pure NMN is $80.00 at the recommended 1,000 mg daily serving.

Two things to check before you compare prices. Several brands print the supplement facts as an image, so the milligram amount is not machine-readable and we could not independently confirm it. And at least one label's own maximum serving (up to four times daily) would turn a $29.97 bottle into about $120 a month, so read the directions, not the headline price.

If you want the honest summary of the field, a 2026 PRISMA-guided systematic review of 113 studies provides it: oral NR and NMN consistently demonstrated biochemical target engagement and were generally well tolerated over weeks to months, while effects on functional, metabolic, vascular and other healthspan-relevant outcomes were heterogeneous and often null or endpoint-specific.

That supports a narrow conclusion. If your goal is a higher NAD+ number, these work. If your goal is to walk faster, grip harder, hold more muscle at 55, or improve your blood sugar, the randomized evidence does not currently show that, and the strongest single sentence in the literature says so directly. Spending $40 to $120 a month for years on that basis is a bet on mechanism over outcome.

There is one more wrinkle worth knowing. A 2026 study found that in whole blood outside the body, nicotinic acid is a potent NAD+ booster while NMN, NR and nicotinamide are not, suggesting NR and NMN may raise circulating NAD+ partly through gut-microbial conversion to nicotinic acid. If that holds, the premium over ordinary niacin is buying a delivery route rather than a unique molecule.

Where the evidence is least bad, it is in disease populations rather than healthy adults: a 90-person trial in peripheral artery disease found a 17.6 meter between-group improvement in six-minute walk distance, and a trial in stable COPD hit its primary endpoint of reduced sputum inflammation. Neither tells a healthy 45-year-old what to expect.

Before starting either compound if you have a history of cancer, are pregnant or breastfeeding, or take prescription medication. Supplements are not screened by the FDA for safety or effectiveness before they go on sale, and an ingredient notification is not an approval. If you are taking a NAD+ precursor for fatigue, that symptom deserves a workup rather than a supplement: anemia, thyroid disease, sleep apnea and depression are all common, testable and treatable causes.