NAD+ supplements are products designed to raise your body’s levels of nicotinamide adenine dinucleotide, a molecule every cell needs to produce energy, repair DNA, and keep metabolism running properly. Rather than containing NAD+ itself (which is too large to absorb through digestion), most supplements contain precursor compounds that your body converts into NAD+ after absorption. The two most common precursors are nicotinamide riboside (NR) and nicotinamide mononucleotide (NMN), both forms of vitamin B3.
What NAD+ Does in Your Body
NAD+ is a cofactor, meaning it assists hundreds of enzymes in performing essential chemical reactions. Its most fundamental role is in energy production: your cells use NAD+ to convert food into ATP, the molecule that fuels virtually every biological process. Without adequate NAD+, your mitochondria (the energy-producing structures inside cells) can’t function efficiently.
Beyond energy, NAD+ activates a family of proteins called sirtuins, which regulate gene expression, protect against cellular stress, and help maintain mitochondrial fitness. NAD+ also fuels enzymes called PARPs, which are critical for DNA repair. PARP1, the most active of these, is the largest consumer of NAD+ in the cell nucleus and plays a key role in maintaining the integrity of your genome. Every time your DNA is damaged by UV light, oxidative stress, or normal metabolic wear, these repair enzymes burn through NAD+ to fix it.
This creates a fundamental tension: the same molecule your cells need for energy is also consumed during stress responses and DNA repair. As demands on NAD+ increase, whether from aging, inflammation, or metabolic dysfunction, the available supply can drop, leaving cells less equipped to handle all three jobs at once.
Why NAD+ Levels Fall With Age
NAD+ levels decline as you get older. This happens partly because the enzymes that consume NAD+ (particularly PARPs and another enzyme called CD38) become more active with age, and partly because the body’s ability to synthesize new NAD+ slows down. The result is a widening gap between supply and demand. Lower NAD+ has been linked in animal studies to hallmarks of aging like mitochondrial dysfunction, impaired DNA repair, and metabolic slowdown. This age-related decline is the central reason NAD+ supplements have attracted so much attention.
NR vs. NMN: How the Precursors Differ
Since NAD+ itself can’t be absorbed through the gut, supplements use smaller molecules your body can convert into NAD+ after they enter your cells. The two main options, NR and NMN, are structurally similar but follow different absorption pathways.
NR can cross cell membranes directly using specialized transporters called equilibrative nucleoside transporters. Once inside, cells convert it into NAD+ through a relatively straightforward process. NMN, on the other hand, carries an extra phosphate group that prevents it from entering cells directly. Instead, NMN must first be converted to NR outside the cell (by an enzyme called CD73 that strips off the phosphate), then transported inside as NR, and finally rebuilt into NAD+. Multiple studies using isotope labeling have confirmed that this extracellular conversion of NMN to NR is the predominant pathway for NAD+ synthesis from NMN supplements.
In practical terms, both precursors end up producing NAD+ through the same final steps. The debate over which is “better” remains active, but the biological evidence suggests NMN takes a detour through NR on its way to becoming NAD+ anyway.
Typical Doses Used in Studies
Most human studies on NMN have used doses of 250 mg per day, with research durations ranging from 10 to 12 weeks. Studies have found health-related effects at doses as low as 250 mg daily and up to 900 mg. In one study involving amateur runners, aerobic benefits were greater at 1,200 mg compared to 300 mg, though there was no meaningful difference between 600 mg and 1,200 mg, suggesting a ceiling effect. Doses up to 1,200 mg daily have been shown to be safe in human trials, though long-term data is still limited.
NR has been studied at doses typically ranging from 250 mg to 1,000 mg per day, though the research base is smaller overall. No official recommended dose exists for either precursor, since neither is classified as an essential nutrient with established daily values.
IV Therapy vs. Oral Supplements
Some clinics offer NAD+ intravenously, delivering the molecule directly into the bloodstream and bypassing the digestive system entirely. Proponents point out that this achieves 100% bioavailability, since nothing is lost to digestion or liver processing. With oral supplements, only a fraction of the precursor dose reaches your cells, and the body still needs to perform the conversion steps to produce NAD+, a process that can be slower in people who are older or under metabolic stress.
The tradeoff is cost and convenience. IV infusions typically cost hundreds of dollars per session, require a clinical setting, and take 1 to 4 hours. Oral precursors are available over the counter at a fraction of the price and can be taken daily at home. Whether the higher bioavailability of IV delivery translates into meaningfully better outcomes compared to consistent oral supplementation hasn’t been established in head-to-head clinical trials.
Regulatory Status in the U.S.
NMN’s regulatory path has been complicated. In late 2022, the FDA initially determined that NMN could not be sold as a dietary supplement, citing its investigation as a new drug. This caused significant disruption in the supplement market. However, in September 2025, the FDA reversed course, determining that NMN is not excluded from the dietary supplement definition. This means NMN can now legally be marketed and sold as a dietary supplement in the United States. NR has been available as a supplement without similar regulatory challenges.
It’s worth noting that “legal to sell as a supplement” is not the same as “FDA-approved.” Like all dietary supplements in the U.S., NAD+ precursors are not evaluated by the FDA for efficacy before they reach store shelves. Quality, purity, and dosing accuracy vary by manufacturer.
Safety and Side Effects
NAD+ precursor supplements are generally considered safe for most people at the doses used in clinical studies. Reported side effects tend to be mild and digestive in nature: nausea, stomach discomfort, diarrhea, and occasional headaches or lightheadedness. Muscle cramps and skin irritation have also been noted. Supplements containing niacin (nicotinic acid), another NAD+ precursor, can cause flushing, a temporary warm, tingling sensation in the skin, and may cause liver toxicity at high doses.
One area of concern involves cancer. Cancer cells have high energy demands, and there’s a theoretical risk that boosting NAD+ could support the growth of existing tumors. This hasn’t been proven, but it remains a serious enough question that people with cancer or a history of cancer should be cautious. The same applies to those with advanced liver disease or who are pregnant or breastfeeding. Long-term safety data for most NAD+ supplements simply doesn’t exist yet, so the risks of taking them for years at a time remain unknown.