NAD+, NR and NMN: What Human Trials Show

Nicotinamide adenine dinucleotide, commonly known as NAD, is a vital coenzyme found in all living cells. It plays a crucial role in energy metabolism, DNA repair, and cellular communication. In recent years, NAD+ has attracted research interest in relation to aging, neurodegenerative diseases, and metabolic health. Most of this interest rests on laboratory and animal studies. Human trials of NAD+ precursors are so far small and short, and they have mostly shown that blood NAD+ levels rise rather than that health outcomes improve.¹ This article reviews what is known about NAD+, its safety profile, what human trials have and have not shown, and practical considerations for anyone thinking about supplementation.

What is NAD+?

NAD+ is a coenzyme involved in redox reactions, carrying electrons from one reaction to another. It exists in two forms: oxidized (NAD+) and reduced (NADH). NAD+ is essential for converting food into energy through cellular respiration, particularly in the mitochondria. Beyond energy production, it also participates in critical cellular processes such as DNA repair and regulation of gene expression.

Biological Functions of NAD+

• Energy Metabolism: NAD+ facilitates the transfer of electrons in metabolic pathways like glycolysis and the citric acid cycle, enabling ATP production.
• DNA Repair: NAD+ is a substrate for enzymes like poly(ADP-ribose) polymerases (PARPs), which repair damaged DNA.
• Cell Signaling: It is a required cofactor for sirtuins, a family of proteins studied for roles in metabolism, inflammation and aging, mostly in laboratory and animal research.

Safety Profile of NAD+

In short clinical trials, oral nicotinamide riboside (NR) and nicotinamide mononucleotide (NMN) have been well tolerated. An 8-week trial of NR at 100, 300 or 1,000 mg/day in overweight adults found no significant difference in adverse events from placebo,² a 60-day trial of NMN at 300 to 900 mg/day in 80 adults found no safety issues,³ and a 2026 meta-analysis of NMN trials (doses of 250 to 2,000 mg/day for 14 days to 24 weeks) found no increase in adverse events.⁴ Some of these trials were funded by, or involved employees of, companies that supply these ingredients.^2,3 These findings apply to oral NR and NMN taken for weeks to months. NAD+ given as an intravenous infusion is a different matter: the evidence is limited, and reported effects include nausea, cramping, flushing and chest discomfort.⁵ There is no established recommended dose of any NAD+ precursor.

The longest NMN trial period in a 2026 meta-analysis was 24 weeks, and long-term safety is not known.⁴ A 2026 safety assessment by the European Food Safety Authority (EFSA) concluded that NMN is safe at up to 300 mg/day for adults, excluding pregnant and lactating women, under the conditions of use it assessed.⁶ Interactions between NR or NMN and medicines have not been well studied, so anyone who takes a prescribed medicine should ask their prescriber or pharmacist before starting. This also applies to people with a health condition, including liver or kidney disease.

Pregnancy, breastfeeding and children. No human safety data on NR or NMN in pregnancy or breastfeeding were identified. EFSA's assessment of NMN applied to adults only and excluded pregnant and lactating women, and it noted effects on reproductive organs in a 90-day study in rats.⁶ Safety in children has not been established. Anyone who is pregnant, breastfeeding or trying to conceive, and parents considering these supplements for a child, should speak to a healthcare professional first.

Cancer. Tumour cells need large amounts of NAD+, and the NAD-producing enzyme NAMPT acts as a cancer-promoting gene in some cancers, which is why NAD+ metabolism is being studied as a target for cancer treatment.⁷ In a 2026 study in pancreatic cancer cells and mice, NMN and nicotinamide reduced the effect of chemotherapy and supported tumour growth.⁸ No human data were identified showing that NR or NMN raise or lower cancer risk, and long-term cancer outcomes have not been studied. As a precaution, people who have or have had cancer, or who are having cancer treatment, should speak to their oncologist before taking these supplements.

High doses and related forms of vitamin B3. In a trial of 20 people with Parkinson's disease, NR at 3,000 mg/day for 4 weeks was well tolerated, but serum homocysteine rose slightly early on, and the authors recommended safety monitoring at that dose.⁹ High-dose nicotinamide, a related form of vitamin B3, can inhibit PARP enzymes that protect DNA and can alter methylation, and a review noted possible epigenetic risks with chronic high-dose use.¹⁰

Potential Side Effects

• In short trials of oral NR and NMN, side effects were not significantly more common than with placebo.^2,4
• Individual reactions, such as stomach upset or headache, can still occur with any supplement. Report any symptoms to a healthcare professional.
• Intravenous NAD+ has been associated with nausea, cramping, flushing and chest discomfort.⁵
• At very high doses, a small early rise in homocysteine was seen with NR,⁹ and high-dose nicotinamide may carry other risks (see above).¹⁰

What Human Trials Show About NAD+ Precursors

Research on NAD+ precursors is evolving. This section summarizes what human trials have and have not shown. Many positive findings come from animal or cell studies, and those results do not necessarily apply to people.

Aging and Longevity

NAD+ is often described as declining with age, but a 2026 analysis of seven human cohorts found that whole-blood NAD+ levels stayed stable with age,¹¹ so it is not established that supplementation corrects an age-related deficit. In rodent studies, raising NAD+ has frequently been associated with improvements in metabolic and mitochondrial measures, although effects varied across models.¹ In people, oral NR and NMN reliably raise NAD-related blood markers, but effects on function and healthspan outcomes have been mixed and often null.¹ Whether they slow aging in people is unknown.

Brain Health and Neurodegenerative Disease

Laboratory studies have suggested that raising NAD+ may protect neurons, but this has not been shown in people. In a phase I trial in 30 people with newly diagnosed Parkinson's disease (NR 1,000 mg/day for 30 days), NR was well tolerated and raised brain NAD levels; the authors reported a mild clinical improvement and said larger trials are needed.¹² In contrast, a 12-week trial in 42 adults with amnestic mild cognitive impairment found that NR roughly doubled blood NAD+ but did not improve cognitive function.¹³ No trial has shown that NAD precursors prevent or treat Alzheimer's or Parkinson's disease.

Metabolic Health

NAD+ is integral to metabolic regulation, but supplementation has not reliably improved metabolic health in people. Two trials of NR in people with overweight or obesity (12 weeks in 40 men, and 6 weeks in 13 adults) found no improvement in insulin sensitivity,^14,15 while one small 10-week trial of NMN in postmenopausal women with prediabetes found better insulin sensitivity in muscle.¹⁶ A 2026 meta-analysis of NMN trials found no significant effects on body weight, fasting glucose, HbA1c or blood lipids.⁴ Results for physical performance are also mixed: a 60-day NMN trial in 80 healthy adults, whose authors included employees of NMN companies, reported longer six-minute walk distances,³ but a 2026 systematic review described functional outcomes across human trials as heterogeneous and often null.¹

Sources of NAD+ and Supplementation

Oral supplements generally contain precursors such as nicotinamide riboside (NR) and nicotinamide mononucleotide (NMN) rather than NAD+ itself. In trials, oral NR and NMN raised NAD+ levels in the blood,^2,3 but this has not been shown to translate into clinical benefit.¹ Intravenous NAD+ is offered in some wellness clinics; a 2026 systematic review found no outcomes trials of it for anti-aging or wellness, and a 2026 narrative review called the evidence preliminary.^1,5 The regulatory status of these compounds differs between countries; in the EU, NMN was assessed as a novel food by EFSA in 2026.⁶

Dietary Sources

• Milk and dairy products
• Fish and meat
• Whole grains
• Vegetables such as mushrooms and green peas

Supplement Forms

• Nicotinamide Riboside (NR): An NAD+ precursor that has been tested in several randomized trials, in which oral doses raised blood NAD+ levels.^2,14,15
• Nicotinamide Mononucleotide (NMN): Another NAD+ precursor, shown to raise blood NAD+ levels in short trials³ and widely discussed in aging research. Evidence of health benefit in people is limited.¹
• Nicotinamide (Vitamin B3): A traditional form of vitamin B3 that the body can use to make NAD+. High doses may carry risks (see above).¹⁰

Practical Considerations for NAD+ Supplementation

Before starting NAD+ supplementation, consider the following:

• Consult Your Healthcare Provider: Especially if you have a chronic illness (including liver or kidney disease), take any prescribed medicine (interactions have not been well studied), are pregnant, breastfeeding or trying to conceive, are considering a supplement for a child, or have or have had cancer. Supplements are not a substitute for prescribed treatment; ask your prescriber or pharmacist before making any change to your medicines.
• Choose Quality Supplements: Look for products with third-party testing and transparent ingredient lists.
• Dosage: No dose of NR or NMN is established for general use, and there are no clinical guidelines. Trials have tested NR at 100 to 2,000 mg/day^2,14 and NMN at 250 to 2,000 mg/day, for weeks to months.⁴ EFSA's 2026 assessment considered NMN safe at up to 300 mg/day in adults, excluding pregnant and lactating women.⁶ Doses above those studied have even less safety information. Follow the directions on the product label and ask a healthcare professional what is appropriate for you.
• Monitor Effects: Track any changes in health or side effects and report them to your healthcare provider.

Frequently Asked Questions (FAQ)

1. What is the difference between NAD+ and NADH?

NAD+ is the oxidized form of nicotinamide adenine dinucleotide, while NADH is the reduced form. NAD+ accepts electrons during metabolic reactions, becoming NADH, which then donates electrons to produce energy.

2. Can NAD+ supplements reverse aging?

No. There is no evidence that NAD+ precursors reverse or slow aging in people. Trials show that oral NR and NMN raise NAD-related blood markers, but effects on function and healthspan outcomes have been mixed and often null.¹ Research is ongoing.

3. Are there any risks associated with NAD+ supplementation?

In short trials, oral NR and NMN were well tolerated, but long-term safety is not established, and neither is safety in pregnancy, breastfeeding or children.^4,6 EFSA concluded in 2026 that NMN is safe at up to 300 mg/day for adults, excluding pregnant and lactating women, under the conditions it assessed.⁶ Intravenous NAD+ has even less evidence and has been associated with nausea, cramping, flushing and chest discomfort.⁵ Interactions with medicines have not been well studied. Talk to a healthcare professional before use, especially if you take medicines, have a medical condition, or have or have had cancer.

4. How quickly do NAD+ supplements work?

In an NR trial, blood NAD+ levels rose within 2 weeks,² but that is a laboratory marker, not a health benefit. Noticeable benefits have not been reliably shown in trials, and individual responses vary.

5. Is NAD+ supplementation effective without lifestyle changes?

Balanced nutrition, regular exercise and adequate sleep are well-established foundations of health. Whether NAD+ precursors add anything on top of them has not been shown, and supplements are not a substitute for these habits.

Key Takeaways

• NAD+ is essential for energy metabolism, DNA repair, and cellular signaling.
• In short trials, oral NR and NMN have been well tolerated; long-term safety is unknown, and safety in pregnancy, breastfeeding and children is not established.
• Evidence that raising NAD+ improves aging, brain or metabolic outcomes in people is limited and mixed, and much of the supporting evidence comes from animal and cell studies.
• In trials, oral NR and NMN raise NAD+ levels in the blood; this has not been shown to translate into health benefits.
• Consult healthcare professionals before starting supplementation, especially if you have a health condition, take medicines, are pregnant or breastfeeding, or have or have had cancer.

References: (1) Gallagher C, et al. Ageing Res Rev. 2026;116:103057. PubMed · DOI (2) Conze D, et al. Sci Rep. 2019;9(1):9772. PubMed · DOI (3) Yi L, et al. Geroscience. 2023;45(1):29-43. PubMed · DOI (4) Yang W, et al. Nutrients. 2026;18(14):2251. PubMed · DOI (5) Alangari A, et al. Front Aging. 2026;7:1887175. PubMed · DOI (6) EFSA Panel on Nutrition, Novel Foods and Food Allergens (NDA), et al. EFSA J. 2026;24(5):e10007. PubMed · DOI (7) Navas LE, et al. Cells. 2022;11(17):2627. PubMed · DOI (8) Nakazzi F, et al. Cancer Lett. 2026;645:218334. PubMed · DOI (9) Berven H, et al. Nat Commun. 2023;14(1):7793. PubMed · DOI (10) Hwang ES, et al. Biomolecules. 2020;10(5):687. PubMed · DOI (11) Trętowicz MM, et al. Nat Metab. 2026;8(6):1282-1290. PubMed · DOI (12) Brakedal B, et al. Cell Metab. 2022;34(3):396-407.e6. PubMed · DOI (13) Martens CR, et al. Alzheimers Dement. 2026;22(7):e71605. PubMed · DOI (14) Dollerup OL, et al. Am J Clin Nutr. 2018;108(2):343-353. PubMed · DOI (15) Remie CME, et al. Am J Clin Nutr. 2020;112(2):413-426. PubMed · DOI (16) Yoshino M, et al. Science. 2021;372(6547):1224-1229. PubMed · DOI

This article is for general information only and is not medical advice. Dietary supplements are not intended to diagnose, treat, cure or prevent any disease. Speak with a doctor, pharmacist or other healthcare professional before starting a supplement, especially if you take medicines, are pregnant or breastfeeding, or have a medical condition.