NAD+ (nicotinamide adenine dinucleotide) is a coenzyme found in every living cell. It is essential for turning food into energy and for enzymes involved in DNA repair. Levels fall with age in several tissues, which is why NAD+ has become central to longevity research.
Strictly speaking, NAD+ is not a peptide. It is a nucleotide, made from two linked nucleotides. It is grouped with peptides because it is sold and discussed in the same longevity and wellness settings, often as an injection.
This guide covers:
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What NAD+ does in the body
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Why levels decline with age
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What human studies of NAD+ and its precursors show
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How IV NAD+ compares with oral precursors
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Safety and regulatory status
What NAD+ Does
NAD+ has two main roles:
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Energy metabolism: it shuttles electrons in the reactions that produce ATP, the cell's energy currency, in mitochondria.
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Signaling and repair: it is consumed by enzymes that regulate cell health, including sirtuins (linked to metabolism and aging), PARPs (DNA repair) and CD38 (immune signaling).
Because those enzymes use NAD+ up, cells must keep making it, mostly by recycling nicotinamide.
Why NAD+ Declines With Age
Studies in animals and some human tissues show NAD+ levels fall with age. Leading explanations include:
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Rising activity of CD38, an NAD+-consuming enzyme that increases with age-related inflammation
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Greater PARP activity as DNA damage accumulates
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Lower activity of NAMPT, the enzyme that drives NAD+ recycling
In mice, restoring NAD+ improved several measures of metabolic and muscle health. Whether raising NAD+ slows aging in humans is unproven.
What the Research Shows
Most human research uses oral precursors rather than NAD+ itself, because NAD+ is poorly absorbed intact.
| Study | Compound and dose | Participants | Main finding |
|---|---|---|---|
| Martens et al., 2018 | NR, 1,000 mg/day for 6 weeks | Healthy middle-aged and older adults | Raised blood NAD+ by about 60%; well tolerated |
| Yoshino et al., 2021 | NMN, 250 mg/day for 10 weeks | Postmenopausal women with prediabetes | Improved muscle insulin sensitivity |
| Grant et al., 2019 | IV NAD+, 750 mg over 6 hours | Healthy men | Plasma NAD+ changed little at first; shows how quickly it is broken down |
NR is nicotinamide riboside and NMN is nicotinamide mononucleotide. Both are converted to NAD+ inside cells.
The results so far are mixed. Precursors reliably raise NAD+ in blood. Effects on blood pressure, muscle function and metabolic markers have been modest or inconsistent across trials.
IV NAD+ vs Oral Precursors
| IV or injected NAD+ | Oral NR or NMN | |
|---|---|---|
| How it works | Delivers NAD+ directly into blood | Converted to NAD+ inside cells |
| Human evidence | Small pilot studies | Multiple randomized trials |
| Common side effects | Flushing, nausea, chest tightness and cramping if infused quickly | Generally mild; occasional nausea or digestive upset |
| Regulatory status | Not an FDA-approved drug | Sold as dietary supplements |
Whether IV NAD+ offers benefits beyond oral precursors has not been tested head to head.
Why the Longevity and Fitness Communities Are Interested
NAD+ sits at the center of several aging pathways at once: energy production, DNA repair and sirtuin activity. That makes it an appealing target for people interested in healthy aging, energy and recovery.
For athletes, NAD+ itself is not on the World Anti-Doping Code's prohibited list. IV infusions of more than 100 mL within 12 hours are a prohibited method, however, unless received during a hospital stay or clinical investigation.
Side Effects and Safety
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Oral precursors: NR and NMN have been well tolerated in trials lasting up to several months.
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IV NAD+: fast infusion commonly causes flushing, nausea, headache, abdominal cramping and chest tightness, which usually ease when the rate is slowed.
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Theoretical concerns: some researchers have questioned whether boosting NAD+ could support the growth of existing tumors, since cancer cells also depend on NAD+. This has not been shown in humans.
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Long-term effects of high-dose supplementation are unknown.
Legal and Regulatory Status
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NAD+ is not approved by the FDA as a drug for any condition.
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NR is sold as a dietary supplement.
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NMN: in 2022 the FDA said NMN could not be sold as a supplement because it had been studied as a drug. The agency reversed that position in September 2025, and NMN is again sold as a supplement.
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IV and injectable NAD+ is offered through clinics and compounding pharmacies.
Who It Is Being Studied For
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Metabolic health: insulin sensitivity and prediabetes.
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Healthy aging: blood pressure, arterial stiffness and muscle function in older adults.
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Neurological conditions: early research in Parkinson's disease.
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Energy and recovery: popular interest, limited controlled evidence.
None of these uses are approved. Talk to a licensed physician before starting NAD+ injections or high-dose precursors.
Disclaimer
This article is for educational and informational purposes only. NAD+ is not approved by the FDA as a drug. Doses described come from published research and are not recommendations for use. Nothing here is medical advice. The Peptide Library is operated in connection with ZenoPeps. Research products are not intended for human consumption.
References
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Martens CR, et al. Chronic nicotinamide riboside supplementation is well-tolerated and elevates NAD+ in healthy middle-aged and older adults. Nature Communications, 2018.
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Yoshino M, et al. Nicotinamide mononucleotide increases muscle insulin sensitivity in prediabetic women. Science, 2021.
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Grant R, et al. A pilot study investigating changes in the human plasma and urine NAD+ metabolome during a 6 hour intravenous infusion of NAD+. Frontiers in Aging Neuroscience, 2019.