NAD supplements are products designed to raise levels of nicotinamide adenine dinucleotide (NAD+), a coenzyme found in every living cell that plays a central role in energy production, DNA repair, and aging. Because NAD+ levels can drop by 50% or more over the course of adult aging, supplements containing NAD+ precursors have become one of the most popular categories in the longevity market. Most products on shelves contain one of two precursor compounds, nicotinamide riboside (NR) or nicotinamide mononucleotide (NMN), rather than NAD+ itself.
What NAD+ Does in Your Body
NAD+ is best understood as a molecular shuttle. It picks up electrons during the breakdown of food (fats, sugars, amino acids) and delivers them to your cells’ power plants, the mitochondria, where they’re used to produce ATP, the energy currency your body runs on. Without adequate NAD+, this energy chain slows down.
Beyond energy, NAD+ fuels two critical repair systems. The first involves proteins called sirtuins, which regulate everything from inflammation to mitochondrial health to gene expression. Sirtuins can only function when NAD+ is available as fuel. The second system involves a DNA-damage sensor called PARP1. When your DNA sustains damage, PARP1 activity can spike up to 500-fold, consuming enormous amounts of NAD+ in the process. Under conditions of persistent DNA damage, this consumption can outstrip the cell’s ability to replenish its NAD+ supply, leaving less available for sirtuins and other processes. The result is a cascade: weaker mitochondria, more oxidative stress, slower DNA repair, and greater vulnerability to further damage.
Why NAD+ Drops With Age
NAD+ decline is one of the more consistent findings in aging research. Human skin samples show NAD+ concentrations dropping at least 50% over the course of adult aging, with levels several-fold lower in adults compared to newborns. The decline shows up across multiple tissues. Human liver samples from people over 60 show roughly a 30% decline compared to those under 45. Brain imaging studies estimate a 10% to 25% drop between young adulthood and old age. Even cerebrospinal fluid shows approximately a 14% decline in people over 45 compared to younger adults.
This decline happens partly because the repair enzyme PARP1 becomes more active as DNA damage accumulates with age, consuming more NAD+. At the same time, the enzymes responsible for making new NAD+ become less efficient. The combination creates a widening gap between supply and demand.
NR vs. NMN: The Two Main Precursors
You won’t find many supplements selling straight NAD+, because the molecule is poorly absorbed through the digestive tract. Instead, most products contain a precursor that your body converts into NAD+ after absorption. The two dominant options are nicotinamide riboside (NR) and nicotinamide mononucleotide (NMN), both derived from vitamin B3.
NR enters cells and gets converted into NMN by enzymes called NR kinases. NMN is then converted into NAD+ by a second set of enzymes. In other words, NR is one step further from NAD+ than NMN is. NMN can also be made directly from nicotinamide (plain vitamin B3) by an enzyme called NAMPT, which is the rate-limiting step in the body’s main NAD+ recycling pathway. NR bypasses that bottleneck entirely, which was part of its early appeal when the pathway was first described in 2004.
In practice, both precursors have shown the ability to raise NAD+ levels in human trials, and neither has emerged as clearly superior. The choice between them often comes down to price, availability, and personal preference.
Typical Dosages Used in Human Trials
Clinical trials have tested a fairly wide range of doses for both precursors. For NR, studies have used anywhere from 100 mg per day up to 2,000 mg per day, with the most common dose being 1,000 mg daily (often split into 500 mg twice a day). Chronic supplementation with NR at doses up to 2,000 mg per day has been reported as safe and well tolerated in these trials.
For NMN, the range in published studies spans 250 mg to 2,000 mg per day. The most frequently studied dose is 250 mg daily, though several trials have used 300 mg, 600 mg, and 1,200 mg per day. Most consumer supplements fall somewhere in the 250 to 500 mg range for NMN and 300 to 1,000 mg for NR.
Oral Supplements vs. Other Delivery Methods
One important caveat: oral NAD+ itself (not the precursors) is poorly absorbed. It gets broken down in the digestive tract before much reaches circulation. This is why precursors like NR and NMN exist as supplements in the first place. They survive digestion better and get converted to NAD+ inside cells.
Intravenous NAD+ infusions bypass the gut entirely, delivering the full dose directly into the bloodstream. This is currently the most reliable method for raising plasma NAD+ levels quickly. However, IV infusions are expensive, time-consuming (sessions can last hours), and require a clinical setting. For people with digestive conditions like inflammatory bowel disease or those who have had bariatric surgery, oral absorption may be particularly unreliable, making injectable routes more appealing. Sublingual formulations (dissolved under the tongue) represent a middle ground, though controlled data on their bioavailability is limited.
Side Effects and Safety Concerns
At typical supplement doses, NAD+ precursors are generally well tolerated. The most commonly reported side effects are mild: headache, dizziness, and nausea, particularly when taken on an empty stomach. These tend to resolve once supplementation stops.
Higher doses raise more specific concerns. Nicotinamide, the basic B3 form that NR and NMN are built from, has been shown to decrease insulin sensitivity in humans at 2 grams per day over two weeks. This is relevant for anyone with prediabetes or type 2 diabetes. High levels of nicotinamide metabolism have also been associated with obesity, liver toxicity, and certain cancers in animal models, though the relevance of these findings to typical human supplement doses remains unclear. The effects of nicotinamide on tumor promotion appear to be organ-specific and stage-dependent, which makes long-term safety difficult to predict from current data.
NMN’s Regulatory Status in the U.S.
NMN had a turbulent few years on the supplement market. In late 2022, the FDA issued a letter suggesting NMN could not be sold as a dietary supplement because a pharmaceutical company had begun investigating it as a drug. This created uncertainty for manufacturers and consumers. In September 2025, the FDA reversed course, determining that NMN is not excluded from the dietary supplement definition. This effectively reinstated NMN’s status as a legal supplement in the United States, and products are now widely available again.
Non-Supplement Ways to Support NAD+ Levels
Supplements aren’t the only lever. Fasting triggers a metabolic switch from glucose burning to fat oxidation and ketone use, which activates sirtuin pathways that depend on NAD+. This creates a positive feedback loop where fasting increases cellular NAD+ levels, potentially improving stress resilience. Calorie restriction and time-restricted eating, particularly limiting meals to daytime hours, appear to offer similar benefits.
Exercise is another well-established stimulus. Physical activity increases the demand for NAD+ in energy production, which in turn upregulates the enzymes that synthesize it. Sleep quality also plays a role, since NAD+ metabolism follows circadian rhythms and disrupted sleep can interfere with its replenishment. For many people, these lifestyle strategies form a foundation that supplements can build on, rather than replace.