By Dr. Mark Rosenberg
NAD+ has become one of the most talked-about molecules in wellness. You hear about it on podcasts, in IV clinics, in supplement ads, and from influencers who imply it can restore youthful energy, sharpen the brain, and “reverse aging.”
The honest answer is more nuanced. NAD+ is biologically important. Raising NAD+ appears possible with certain precursors. Some human studies suggest potential benefits in cellular energy metabolism, mitochondrial function, insulin sensitivity, fatigue, and possibly cognitive or neurologic settings. But the science does not yet support many of the dramatic claims being made online.
What is NAD+?
NAD+ stands for nicotinamide adenine dinucleotide. In plain English, it is a coenzyme found in every cell of the body. You can think of it as a molecular helper that allows enzymes to do their job.
One of NAD+’s major roles is energy production. It helps shuttle electrons through the biochemical pathways that convert food into usable cellular energy, especially inside mitochondria. NAD+ also participates in DNA repair, cellular stress responses, metabolism, and the activity of enzymes such as sirtuins and PARPs, which are involved in maintaining normal cell function. Cleveland Clinic describes NAD as essential for turning food into energy and helping cells repair DNA. NAD+ is not a stimulant. It is not caffeine. It does not “force” energy. It supports the cellular machinery that helps produce energy.
Why NAD+ declines with age:
NAD+ levels tend to decline with age. That decline appears to happen for several reasons: increased NAD+ consumption by DNA-repair and inflammatory pathways, reduced recycling of NAD+ precursors, mitochondrial stress, metabolic disease, and possibly reduced activity of enzymes involved in NAD+ synthesis.
Functionally, lower NAD+ availability may make cells less efficient at energy production and repair. That does not mean NAD+ decline is the single cause of aging. Aging is far more complex. But NAD+ sits at the intersection of metabolism, mitochondrial function, DNA repair, inflammation, and cellular resilience, which explains why researchers are interested in it.
Lower NAD+ has been linked with age-associated conditions including metabolic dysfunction, cognitive decline, cardiovascular disease, muscle weakness, and fatigue, although “linked with” does not always mean “causes.”
What the evidence supports:
The strongest statement we can make is this: NAD+ biology matters, and NAD+ precursors can raise NAD+ levels in humans.
Oral precursors such as nicotinamide riboside, or NR, and nicotinamide mononucleotide, or NMN, have been shown in human studies to increase NAD+ or NAD+-related metabolites. A 2025 randomized trial of NR in long-COVID patients found that NR increased NAD+ levels within five weeks, but did not significantly improve objective cognitive outcomes compared with placebo; exploratory findings suggested possible improvements in fatigue, sleep, and mood that require larger trials.
NMN also has human data. In a small clinical trial of postmenopausal women with overweight or obesity and prediabetes, NMN improved muscle insulin sensitivity and insulin signaling. A 2024 systematic review of randomized trials concluded that NMN was generally well tolerated and showed nonsignificant improvements in some physical performance measures.
So the credible areas of interest include cellular energy metabolism, mitochondrial function, insulin sensitivity, fatigue-related states, and possibly neurologic or cognitive applications. But the key word is supports, not cures.
What the evidence does not support:
NAD+ does not have convincing human evidence showing that it “reverses aging.” It has not been proven to cure Alzheimer’s disease, Parkinson’s disease, cancer, chronic fatigue syndrome, long-COVID, addiction, or metabolic disease. It should not be marketed or thought of as a dramatic overnight transformation.
Some people report feeling more energy after NAD+ therapy or precursors. Others feel nothing. Both responses are believable. If your baseline NAD+ metabolism is not the limiting factor in your fatigue, raising NAD+ may not make you feel dramatically different.
For many patients, poor sleep, overtraining, low protein intake, insulin resistance, thyroid dysfunction, anemia, depression, medication effects, alcohol use, and chronic inflammation are more important drivers of fatigue than NAD+ status alone.
Delivery methods: IV, subcutaneous, NMN, and NR:
This is where marketing often gets ahead of science.
IV NAD+
IV NAD+ is popular in wellness clinics because it feels medical and premium. It bypasses the gut and puts NAD+ directly into the bloodstream. But that does not automatically mean it is the best way to raise intracellular NAD+ where it matters. NAD+ is a charged molecule, and cellular uptake is more complicated than simply “put it in the blood and it enters every cell.”
Human pharmacokinetic studies of IV NAD+ are limited. One IV NAD+ study measured changes in plasma and urinary NAD+ metabolites during and after infusion, showing that IV delivery changes the NAD metabolome, but this does not prove superior clinical outcomes. A 2026 human study comparing commercially administered IV NAD+ and IV NR focused on tolerability, safety markers, and infusion characteristics, underscoring that clinical outcome data are still early.
Subcutaneous NAD+
Subcutaneous NAD+ injections are used by some clinicians, but high-quality human outcome data are sparse. They may be more convenient than IV therapy, but we still need better studies on dosing, absorption, tissue effects, and clinical outcomes.
Oral NR and NMN
Oral NR and NMN have the strongest practical evidence for raising NAD+-related metabolites in humans. They are easier, less expensive, and better studied than many clinic-based injectable protocols. That does not mean they are magic. It means they are currently the most evidence-grounded route for most wellness-oriented patients.
As of late 2025, FDA-related positioning on NMN changed: the FDA confirmed NMN is not categorically excluded from being a dietary supplement, although companies still face New Dietary Ingredient and compliance requirements.
What should a patient realistically feel?
Some people report improved energy, mental clarity, exercise tolerance, or recovery within a few weeks. Others notice subtler effects over eight to twelve weeks. Some notice nothing.
A reasonable trial period for oral NR or NMN is often 8–12 weeks, paired with objective tracking: sleep, training recovery, fasting glucose or insulin markers when appropriate, body composition, energy levels, and cognition. If nothing changes, it may not be worth continuing.
IV NAD+ may produce an acute sensation during or after infusion, but acute subjective effects do not necessarily prove long-term cellular benefit.
Safety, contraindications, and who should avoid it:
NR and NMN appear generally well tolerated in short-term studies. Possible side effects include nausea, flushing, headache, GI upset, fatigue, insomnia, or changes in methylation-related metabolites, depending on dose and formulation. Long-term safety data remain limited.
People who should be cautious or avoid NAD+ therapy unless supervised include those who are pregnant or breastfeeding, people with active cancer, those receiving chemotherapy or radiation, patients with severe liver or kidney disease, people with bipolar disorder or severe anxiety who may be sensitive to activating supplements, and anyone taking complex medication regimens.
The cancer question deserves special caution. NAD+ supports normal cellular repair and metabolism, but cancer cells also use NAD+ pathways. That does not mean NAD+ “causes cancer,” but it does mean high-dose NAD+ strategies should not be used casually in patients with active malignancy.
Not just wellness hype:
NAD+ is real biology, not just wellness hype. But the claims around it are often inflated. It may support cellular energy metabolism and mitochondrial function, and oral precursors such as NR and NMN can raise NAD+-related markers. What it has not proven is that it reverses aging, cures disease, or produces dramatic overnight changes.
For the right patient, NAD+ support may be reasonable. But it should be part of a broader plan: strength training, protein, sleep, metabolic health, nutrient sufficiency, and medical evaluation for real causes of fatigue.