NAD+

NAD+ (Nicotinamide Adenine Dinucleotide) is a coenzyme your cells use for almost every energy-producing reaction. Mitochondria need it to turn food into ATP, DNA-repair enzymes need it to fix damage, and a family of regulatory proteins called sirtuins burn it as fuel. Levels drop substantially with age, and that decline is one of the better-supported mechanistic explanations for why older cells run slower, repair worse, and accumulate damage faster than young ones.

There are two ways to actually raise NAD+ in the body. The most common is oral precursors, NMN (nicotinamide mononucleotide) or NR (nicotinamide riboside), which the body uses to build NAD+ internally. Oral NAD+ itself isn't well absorbed because the molecule is too large and unstable to make it through the gut intact, so the precursor route is what works for pills and capsules. The other route is injecting NAD+ directly, either as an IV drip or as subcutaneous shots, which is increasingly popular in the wellness and longevity scene and produces effects that some users say oral precursors don't. Both routes raise NAD+ in the body, they just do it differently and at very different cost.

Most people take it hoping for steadier energy, better recovery, and slower biological aging. The energy and recovery effects are real but subtle. The longevity claims are still ahead of the human evidence, which is what most of this page is about.

Deep-dive

Why NAD+ matters at all. NAD+ is a redox cofactor, meaning it shuttles electrons during energy production. Every time a mitochondrion converts glucose or fat into ATP, NAD+ is part of the chain. But it also has a second life as a signalling substrate. Three families of enzymes consume NAD+ as fuel: sirtuins (which deacetylate proteins involved in metabolism, DNA repair, and stress resistance), PARPs (which repair DNA double-strand breaks), and CD38 (an ectoenzyme on immune cells that ramps up with inflammation). When NAD+ runs low, all three of these systems slow down at once. Sirtuin-driven mitochondrial maintenance suffers, DNA damage accumulates, and inflammatory signalling tilts upward.

Why levels decline with age. The decline isn't mainly about reduced production. It's about increased consumption. CD38 expression rises substantially with age in multiple tissues, and CD38 is one of the most NAD+-hungry enzymes in the body. Chronic low-grade inflammation drives CD38 up further. PARPs also work harder as DNA damage accumulates. Meanwhile, NAMPT (the rate-limiting enzyme that recycles nicotinamide back into the salvage pathway) tends to drop. The net effect is that older tissues are simultaneously burning NAD+ faster and rebuilding it slower. By 60, tissue NAD+ in some compartments is roughly half what it was at 30.

NMN vs NR vs nicotinamide. All three feed into NAD+, but they enter the pathway at different points. Nicotinamide (NAM, plain vitamin B3) is the cheapest and crosses cell membranes easily, but at high doses it can inhibit sirtuins (the very enzymes you're trying to feed) and drive methylation demand. NR (nicotinamide riboside) is the most studied in humans, with consistent evidence that 300-1000 mg/day raises blood NAD+ by 40-60% within a few weeks. NMN sits one step closer to NAD+ on the pathway and has comparable human pharmacokinetic data at 250-1250 mg/day. The endless internet debate about which is better is largely overblown. Both raise NAD+. Neither has shown a decisive clinical edge over the other in a head-to-head trial.

What it actually does in humans. Strip away the hype and the human evidence settles into a few defensible buckets. Cardiovascular: a crossover trial in middle-aged adults showed 1000 mg/day of NR for 6 weeks reduced systolic blood pressure by ~10 mmHg in those with elevated baseline BP, with a smaller effect on aortic stiffness. A meta-analysis of NMN trials found a roughly 2 mmHg reduction in diastolic BP, modest but real. Metabolic: Yoshino's 2021 trial in postmenopausal women with prediabetes found 250 mg of NMN for 10 weeks improved muscle insulin sensitivity by ~25%, although the trial had a randomisation imbalance that complicates interpretation, and a later meta-analysis of 8 NMN trials found no consistent effect on glucose markers in healthy adults. Performance: a trial in amateur runners found 600-1200 mg/day of NMN over 6 weeks raised ventilatory threshold (a marker of aerobic capacity), although VO2 max itself didn't change. Muscle function: 12 weeks of 250 mg NMN in older men modestly improved gait speed and grip strength. Neurological: the NADPARK trial showed 1000 mg/day of NR for 30 days raised brain NAD+ in Parkinson's patients and produced mild clinical improvement; followup trials at up to 3000 mg/day are ongoing. Skin cancer: nicotinamide (the simpler precursor) at 500 mg twice daily reduced new non-melanoma skin cancers by 23% in the ONTRAC trial in high-risk patients, although the same dose failed to replicate in transplant recipients.

What it doesn't reliably do. A recent double-blind cognition trial found NAD+ supplementation did not improve cognition more than placebo in healthy adults, although effect sizes hinted larger trials might find something. NMN has not consistently improved fasting glucose, HbA1c, or lipids in healthy people. It has not been shown to extend lifespan in humans (no human longevity trial exists for any precursor, and won't for decades). The honest summary: precursors raise NAD+, NAD+ supports several systems that decline with age, and a handful of those downstream systems show measurable improvement. Whether this adds years or just makes existing years run a bit better is unanswered.

Women. The evidence base is reasonably balanced. Yoshino's landmark NMN trial enrolled only postmenopausal women, which is unusual in this field and produced the strongest metabolic finding to date. NR cardiovascular trials have included women and men with similar effects. The 12-week NMN safety trial in healthy adult men and women found no sex-specific adverse events. CD38 expression rises faster in women after menopause, partly because oestrogen suppresses inflammatory CD38 activity, which is one mechanistic reason older women may have lower NAD+ than age-matched men and may respond well to precursors. No dose adjustment by sex is needed, but post-menopausal women with metabolic concerns are arguably the population with the strongest case for trying NMN based on existing evidence. Skip during pregnancy and breastfeeding, no safety data.

Injections and IVs. Injecting NAD+ directly is a real and growing category, distinct from oral precursors. IV NAD+ drips (typically 250-1000 mg per session over 2-4 hours) are widely used in longevity clinics, addiction recovery, and wellness centres, with consistent subjective reports of mental clarity, energy, and reduced cravings. Subcutaneous NAD+ injections (50-100 mg, 1-3x weekly) have become popular as a more practical and self-administered alternative to IVs, at a fraction of the cost. Subcutaneous injections of nicotinamide riboside chloride (Niagen Plus) are also now in a phase 1 trial in healthy adults.

The formal evidence base is thin. There are no large peer-reviewed RCTs of IV NAD+ in healthy people, and pilot data suggests a meaningful fraction of an IV NAD+ dose appears in urine unchanged, meaning not all of it enters cells intact. Mechanistically, much of the injected NAD+ is likely broken down extracellularly to nicotinamide and nicotinamide riboside, which are then transported into cells, the same downstream pathway as oral precursors. But the subjective response many users report from injections is hard to fully explain by oral-equivalent biochemistry alone, and dismissing it as pure placebo is probably too neat. The truth is somewhere between "this is a magic shortcut" and "this is just expensive oral precursors", and the trial data to settle it doesn't exist yet.

Practical take: oral precursors are cheaper, well-studied, and work for most goals. Injections are worth considering if you're not getting a felt response from oral, if you're recovering from addiction (where IV NAD+ has the most clinical experience behind it, even if not yet RCT-validated), or if you specifically want the higher-impact, faster-acting subjective effect that injections seem to deliver. If you go that route, subcutaneous self-injection is more accessible and far cheaper than IV (clinics typically charge $300-1000 per IV session in the US), but quality of source, sterility, and dosing protocol matter a lot. Don't source from random suppliers.

Lifestyle context. The biggest non-supplement levers on NAD+ are exercise (which upregulates NAMPT and improves NAD+ recycling), avoiding excess inflammation (CD38 activation depletes NAD+), and not chronically over-consuming alcohol (which heavily taxes NAD+ via ethanol metabolism). A person who exercises, sleeps, and eats reasonably will have better NAD+ status than a sedentary person on a megadose of NMN. Supplementation is additive, not corrective.

Dosage:

NMN: 250-500 mg/day for general use, taken in the morning. 500-1000 mg/day if you're over 50, post-menopausal, or specifically targeting metabolic or cardiovascular markers. Doses up to 1250 mg/day have been tested safely for 4 weeks but the cost-benefit above 500-600 mg flattens out for most people

NR: 300-600 mg/day for general use. 1000 mg/day if you're targeting blood pressure or arterial stiffness, which is the dose used in the Seals/Martens cardiovascular trials. Higher doses (up to 3000 mg/day) have been used in Parkinson's trials but aren't relevant outside that context

Niacinamide: 500 mg once or twice daily if your specific goal is skin cancer prevention and you're high-risk (history of multiple non-melanoma skin cancers). This is the only NAD+ precursor with a phase 3 cancer-prevention trial behind it. Not a general anti-aging dose, you wouldn't take this much chronically without that specific indication, since high-dose niacinamide can mildly inhibit sirtuins

Timing: Take in the morning or early afternoon. NAD+ has a circadian rhythm and supplementing late can interfere with sleep in some people. Doesn't need to be taken with food

Cycling: No clear evidence that cycling matters, but most long-term users alternate periods of higher and lower doses. There's no withdrawal

Forms: Plain capsules or tablets are fine for oral. Liposomal and sublingual formulations claim better absorption but lack good comparative trials

Subcutaneous NAD+ injection: 50-100 mg, 1-3x weekly is the typical protocol in longevity clinics. Start at 50 mg once weekly to gauge tolerance (flushing, nausea, injection site irritation), then titrate up. Inject into abdominal fat or back of upper arm, rotate sites. Quality and sterility of the compounded source matter more here than for oral. Self-injection works once you're trained on it but the source has to come from a reputable compounding pharmacy

IV NAD+: 250-1000 mg per session, infused slowly over 2-4 hours to minimise flushing, nausea, and chest pressure. Faster infusions feel awful. Typically done weekly to monthly depending on protocol. Mostly only worth it if subcutaneous isn't an option for you, since cost runs $300-1000 per session

Stack with TMG (trimethylglycine, 500-1000 mg/day) if you're on higher doses long-term. All NAD+ precursors increase methylation demand because nicotinamide gets methylated for excretion. TMG donates methyl groups and keeps homocysteine in check. This matters more above 1000 mg/day of NMN or NR. If you're on lower doses with adequate B12, folate, and choline intake, you probably don't need it

Start low if you're on blood pressure medication. NR in particular has a real BP-lowering effect in people with elevated baseline BP. Check pressure for the first few weeks and adjust if needed

Here's what you can expect:

The honest answer is that most healthy people don't notice much in the first few weeks. NAD+ precursors don't produce a stimulant-like signal. Blood NAD+ rises within days, but the downstream effects (mitochondrial efficiency, DNA repair throughput, sirtuin activity) take weeks to translate into anything you'd consciously notice, and even then the effect is usually subtle.

What people who do respond tend to report, after 4-8 weeks: a slightly steadier energy curve through the day with less of an afternoon crash, faster recovery from hard training, better sleep quality (sometimes, though some people get the opposite if they take it late), and modest cognitive clarity. None of this is dramatic. If you're expecting to feel younger, you'll be disappointed. If you're expecting subtle drift in the right direction over a couple of months, you're calibrated correctly.

The more measurable effects are blood pressure (a real ~5-10 mmHg systolic drop in people with elevated baseline BP), insulin sensitivity (in people with prediabetes), and aerobic capacity in trained individuals adding precursors to a training programme. If you have none of these starting points, supplementation will probably feel like nothing for a long time. The longevity case is mechanistic and indirect, so by definition you won't feel it.

A reasonable trial is 8-12 weeks at 500 mg/day of NMN or NR, ideally with before-and-after bloodwork and blood pressure if relevant. If you notice nothing, don't show measurable change, and don't have an underlying reason to keep going, stop. This isn't a compound where stacking longer makes the difference clearer.

Side effects & risks:

Mild GI upset (nausea, loose stools) is the most common side effect, especially when starting or at doses above 600 mg. Usually resolves within a week or two, or by splitting the dose between morning and midday

Headache and flushing are occasional, more common with niacinamide than NMN or NR. Doesn't typically last

Insomnia or vivid dreams if taken late in the day. NAD+ has circadian effects on the brain. Move the dose earlier and this resolves

Mild blood pressure drop is real, particularly with NR at 1000 mg/day. Beneficial if your BP is elevated, worth watching if you're already low or on antihypertensive medication

Homocysteine elevation is a theoretical concern at high doses because nicotinamide is methylated for excretion. The high-dose NR Parkinson's trial saw a small initial rise in homocysteine at 3000 mg/day that didn't progress, with the methyl donor pool intact. At standard doses (250-500 mg) this is unlikely to matter, but it's the main reason TMG gets recommended at higher doses

Cancer concerns are unresolved. Cancer cells can use NAD+ to fuel their own growth, and a preclinical mouse study found NMN supplementation made UV-induced skin cancers more aggressive. Counterpoint: nicotinamide at 500 mg twice daily reduced non-melanoma skin cancers in the ONTRAC trial in immunocompetent humans. The honest summary is that the relationship between NAD+ supplementation and cancer risk is context-dependent and unsettled. If you have an active cancer or recent cancer history, do not start NAD+ precursors without oncology input

Long-term safety data is genuinely thin. The longest published RCT runs 12 weeks for NMN, 6 weeks for NR in healthy adults, and one Parkinson's study has run two years. Multi-year human safety data of the kind that exists for established vitamins doesn't exist for these compounds. This doesn't mean they're unsafe, it means we don't know

Interactions: Caution with antihypertensive medication (additive BP-lowering). Caution with chemotherapy and immunosuppressants. Otherwise low interaction profile

Pregnancy and breastfeeding: Skip. No safety data. Standard B3 from food and prenatals is sufficient

Quality is genuinely variable. The NMN supplement market has a known problem with mislabelled and underdosed products. Independent testing in 2022 found a substantial fraction of top-selling NMN brands contained far less NMN than labelled. Buy from brands with third-party testing (Certificate of Analysis available, ideally NSF or USP). For NR, the Niagen-branded form has the most established quality control

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Blood markers

Blood pressure, baseline and after 4-8 weeks. The most reliably measurable effect of NAD+ precursors. If you have elevated baseline BP, this is also where you'll see the strongest response. If you're already low or on medication, monitor for over-correction.

Fasting glucose, HbA1c, fasting insulin (HOMA-IR), baseline if you're taking it for metabolic reasons (prediabetes, post-menopausal weight gain, insulin resistance). Recheck at 12 weeks. The metabolic effect is real but small and you need bloodwork to see it.

Homocysteine, baseline if you're planning to run higher doses (1000+ mg/day) chronically, and after 8-12 weeks. If it drifts up, add TMG 500-1000 mg/day. Less critical at standard 250-500 mg doses.

Comprehensive metabolic panel (liver enzymes, kidney markers), baseline if you're running high doses or have any underlying organ issues. NAD+ precursors aren't known hepatotoxins but long-term high-dose data is limited.

NAD+ itself can be measured by dried blood spot or finger-stick tests sold direct-to-consumer. The clinical utility is limited because reference ranges are still being established and intra-individual variation is high. Useful as a directional check (did supplementation move the needle for me?) rather than a diagnostic.

For most people taking 250-500 mg/day of NMN or NR for general use, baseline BP and a standard annual blood panel covers it. The people who actually benefit from richer baseline testing are those with elevated BP, prediabetes or metabolic syndrome, anyone running 1000+ mg/day chronically, and anyone stacking with other longevity compounds.

Sold as a dietary supplement in most countries. NMN's regulatory status in the US shifted in 2025 when the FDA reversed its earlier exclusion ruling and confirmed NMN can be lawfully marketed as a supplement. NR has been a confirmed dietary ingredient in the US throughout. Both are widely available without prescription.