NR, short for nicotinamide riboside, is a form of vitamin B3 sold as a dietary supplement to boost levels of NAD+, a molecule your cells need to produce energy, repair DNA, and carry out hundreds of metabolic reactions. NAD+ levels naturally decline with age, and NR is one of the most studied compounds for raising them back up. In human trials, two weeks of NR supplementation roughly doubled NAD+ concentrations in the blood.
How NR Works in Your Body
Every cell in your body relies on NAD+ (nicotinamide adenine dinucleotide) as a workhorse molecule. It shuttles electrons during energy production, activates proteins involved in DNA repair, and helps regulate your internal clock. By your 40s and 50s, NAD+ levels have dropped significantly compared to your 20s, which researchers believe contributes to age-related declines in energy, muscle function, and cellular resilience.
NR enters your cells through dedicated transport channels and gets converted into NAD+ in a two-step process. First, enzymes called NRK1 and NRK2 add a phosphate group to NR, turning it into NMN (another popular supplement). Then a second enzyme converts NMN into NAD+. This pathway is distinct from the one your body uses to recycle other forms of vitamin B3, which relies on a different, rate-limited enzyme. That distinction matters because it means NR can potentially top up NAD+ through an alternative route that isn’t bottlenecked the same way.
What Human Trials Actually Show
A randomized study of 65 healthy adults found that 14 days of NR supplementation increased whole-blood NAD+ concentrations by about twofold compared to placebo. The effect was sustained rather than transient, unlike plain nicotinamide (the common form of B3 in multivitamins), which only spiked NAD+ briefly before returning to baseline. NMN, the other popular NAD+ precursor, performed comparably to NR over the same two-week period.
In a five-month trial using identical twins, NR at doses escalating from 250 to 1,000 mg per day increased mitochondrial DNA in skeletal muscle by about 30% and boosted the number of mitochondria in muscle fibers by roughly 14%. Mitochondria are the structures inside cells that generate energy, so more of them generally means greater capacity for sustained physical effort. The supplement also activated several genes involved in building new mitochondria, including SIRT1, a protein linked to longevity research.
The metabolic picture is more mixed. That same twin study found NR did not improve body composition, insulin sensitivity, or standard markers of metabolic health. A separate 12-week trial in obese, insulin-resistant men also found no improvement in insulin sensitivity or muscle mitochondrial function. One trial in healthy middle-aged and older adults showed a trend toward lower systolic blood pressure, particularly in people whose baseline readings fell between 120 and 139 mmHg, but the effect wasn’t strong enough to be definitive.
NR vs. NMN: Key Differences
NR and NMN are closely related. NMN is actually one step closer to NAD+ in the conversion pathway, which has led some people to assume it’s more efficient. The reality is less clear-cut. NR has well-characterized transport channels that move it directly into cells. How NMN gets into cells is still debated: it may enter through its own transporter, or it may first get converted back into NR outside the cell before being absorbed.
In the head-to-head human trial that tested both, NR and NMN raised blood NAD+ levels by nearly identical amounts after 14 days. One practical difference is stability. NR appears to break down into plain nicotinamide more readily in blood plasma, meaning some of it may lose its advantage before reaching tissues. NMN, on the other hand, has been shown to raise NAD+ robustly in liver tissue even in animals that lack the enzyme NR depends on, suggesting it can take alternative routes. For most consumers, the two supplements deliver similar results at comparable doses, and neither has a clear, proven edge over the other in human studies.
Dosage and How Long It Takes
Most human trials have used between 250 and 1,000 mg of NR per day. Three studies tested 2,000 mg daily, and a safety trial in Parkinson’s disease patients pushed the dose to 3,000 mg daily for four weeks without moderate or severe side effects. Doses above 2,000 mg have not been tested long-term in humans. The five-month twin study at 1,000 mg per day found no adverse effects over that extended period.
Based on the available data, NAD+ levels in the blood begin rising within hours of taking NR. By 14 days, blood NAD+ concentrations roughly double compared to baseline and remain elevated with continued use. Effects on deeper tissues like muscle mitochondria took longer to emerge in studies, showing up over weeks to months of consistent supplementation.
Side Effects
NR is generally well tolerated. In a safety trial testing 3,000 mg per day (well above typical supplement doses), all reported side effects were classified as mild. The most common were headache, nausea, indigestion, fatigue, and muscle cramps. Importantly, the frequency of these side effects was not significantly different between the NR group and the placebo group, meaning some of these complaints may not have been caused by NR at all. All cases of nausea and indigestion resolved by the end of the study period.
One notable finding from the twin study: markers of glucose metabolism shifted slightly in a less favorable direction during supplementation, though all values remained within normal ranges. This didn’t translate into diabetes or any clinical concern, but it’s a pattern researchers have flagged for further investigation.
Regulatory Status and Food Sources
The FDA has reviewed nicotinamide riboside chloride (the form used in supplements) through its GRAS (Generally Recognized as Safe) notification process and responded with “no questions,” meaning the agency did not object to its safety for use in food and supplements. NR supplements are sold over the counter and do not require a prescription.
NR also occurs naturally in food, though in tiny amounts. The richest plant sources identified so far include wild chicory (about 1,644 micrograms per 100 grams), banana (1,209 micrograms), and orange (1,013 micrograms). For context, even the richest food source delivers roughly 1.6 mg per 100 grams of food. A typical supplement capsule contains 250 to 300 mg, so getting meaningful doses from diet alone isn’t realistic.
Who Might Benefit Most
Because NAD+ declines with age, older adults are the population with the most theoretical reason to supplement. A study in aged individuals found that three weeks of NR boosted NAD+ in the blood, though it did not detectably raise NAD+ in skeletal muscle over that short timeframe. In young, healthy animals, increasing NAD+ in muscle had almost no observable effect, suggesting the benefit is most relevant when levels have already dropped.
The current evidence supports NR as a reliable way to raise blood NAD+ levels in humans. What that translates to in terms of day-to-day health improvements is still being worked out. The muscle mitochondria findings from the twin study are promising, but improvements in metabolism, cardiovascular health, or physical performance have not been consistently demonstrated across trials. For now, NR is best understood as a well-tolerated supplement with a clear biochemical effect and plausible but still-unproven long-term health benefits.