NAD+

Think of NAD+ as the fuel that lets the cell's recharge crew do their job. The bottleneck with ageing isn't only that the tank runs low — it's that nobody has shown that refilling the tank actually gets the engine running like new again. Pouring fuel into a car proves the gauge moves; it doesn't prove the car will suddenly drive further or faster, and that's exactly the gap the human data hasn't closed.

NAD+ works in two distinct modes. As a redox coenzyme it cycles between NAD+ and NADH to carry electrons through the metabolic pathways (glycolysis, TCA cycle, oxidative phosphorylation) that generate cellular ATP. As a signalling substrate it is consumed by enzymes — the sirtuins (which deacetylate proteins controlling mitochondrial biogenesis, stress resistance and gene expression), the PARPs (DNA repair), and NADases such as CD38. With age, tissue NAD+ falls, partly through increased CD38-driven consumption and reduced salvage synthesis, and this decline is linked in animal models to mitochondrial dysfunction. The intended therapeutic effect is to restore NAD+ — directly by infusion/injection, or indirectly by feeding cells precursors (NR, NMN, niacin) that are enzymatically converted to NAD+ — thereby reactivating sirtuin- and PARP-dependent repair and metabolic programmes.

Research contexts. Not proven uses, and not recommendations.

More than a dozen human trials of NAD+ precursors (mainly nicotinamide riboside and NMN), some up to 6 months, consistently show two things: they are safe and well tolerated, and they reliably raise blood NAD+ levels. The much-cited Martens et al. (2018, Nature Communications) placebo-controlled crossover in 24 middle-aged/older adults confirmed NR roughly doubled NAD+ and hinted at reduced blood pressure and arterial stiffness — but only as exploratory signals that did not survive statistical correction. Beyond raising the biomarker, robust clinical benefit is largely missing: human studies have shown only limited efficacy for metabolic endpoints, and the overall evidence for mitigating age-related disease is weak. Direct IV NAD+ — the version sold in wellness clinics — is barely studied: the main human data are tiny pharmacokinetic/tolerability pilots (e.g. Grant et al. 2019, n=11), which found infused NAD+ is rapidly cleared from plasma and largely catabolised, with no efficacy outcomes. Most trials testing genuine anti-ageing or neuroprotective benefit are ongoing or not yet reported. In short: the biology is real, the biomarker moves, the human payoff is unproven.

• !The biomarker (raised NAD+) is not the same as a clinical benefit — moving the number proves very little about ageing, energy or longevity in humans.
• !Direct IV NAD+, the form most heavily marketed by clinics, has the least evidence and is largely catabolised before reaching tissues intact.
• !IV infusions commonly cause unpleasant dose-rate effects: chest pressure, flushing, nausea, abdominal cramping, anxiety — usually managed by slowing the drip, but it reflects how fast it's pushed.
• !Marketing massively outruns the science; 'reverses ageing' and addiction-cure claims are not supported by controlled human data.
• !Theoretical concern that boosting NAD+ could also fuel processes you don't want amplified (e.g. supporting some tumour metabolism) — unresolved, not a proven harm, but a reason for caution.
• !Private clinic quality varies: unlicensed 'specials', variable sourcing, and practitioners of varying qualification.

NAD+ itself is not licensed as a medicine by the MHRA for any therapeutic indication, and no NAD+ IV or injectable product holds a UK or EU marketing authorisation. When given for a medical purpose it can only be supplied legally as an unlicensed 'special' medicinal product, made or imported by an MHRA-registered specials manufacturer, against a prescription from a doctor or other authorised prescriber for a specific patient's needs. Unlicensed medicines cannot be advertised to the public. IV NAD+ is delivered through private wellness clinics rather than the NHS; clinics carrying out such regulated activity should be CQC-registered with appropriately registered prescribers (GMC/NMC). The precursor vitamins are treated differently and are sold as foods rather than medicines: nicotinamide riboside (NR) is marketed as a food supplement, while nicotinamide mononucleotide (NMN) is currently a novel food 'under assessment' by the Food Standards Agency in Great Britain (not yet authorised, but available transitionally). Neither precursor is MHRA-licensed to treat any disease, and medicinal claims for them would bring them under MHRA control.

• · Phase I/II· Completed

  Nicotinamide riboside in healthy middle-aged and older adults (Martens et al.)

  Established safety and NAD+ elevation; cardiovascular signals exploratory only.

• · Phase I (NADPARK) / Phase III (NO-PARK)· NADPARK completed; NO-PARK ongoing

  Nicotinamide riboside in Parkinson's disease (NADPARK / NO-PARK programme)

  NADPARK was a 30-patient phase I pilot showing raised brain NAD+; NO-PARK (~400 participants) tests whether boosting NAD+ alters Parkinson's progression — among the most rigorous clinical tests of the hypothesis.

• · Pilot· Completed

  IV NAD+ metabolome pilot (Grant et al.)

  Pharmacokinetics/tolerability of direct IV NAD+; no efficacy endpoints.

1. 01
   Chronic nicotinamide riboside supplementation is well-tolerated and elevates NAD+ in healthy middle-aged and older adults — Martens CR, et al., Nature Communications (2018)

   Double-blind placebo-controlled crossover (24 completers): NR safely roughly doubled blood NAD+; cardiovascular benefits were only exploratory.

2. 02
   A Pilot Study Investigating Changes in the Human Plasma and Urine NAD+ Metabolome During a 6 Hour Intravenous Infusion of NAD+ — Grant R, et al., Frontiers in Aging Neuroscience (2019)

   n=11 pharmacokinetic pilot: infused NAD+ is rapidly cleared and largely catabolised; no efficacy endpoints. The main human IV-NAD+ data.

3. 03
   NAD+ and sirtuins in aging and disease — Imai S, Guarente L, Trends in Cell Biology (2014)

   Foundational mechanism review of NAD+, the salvage pathway and sirtuins in ageing.

4. 04
   CD38 dictates age-related NAD decline and mitochondrial dysfunction through an SIRT3-dependent mechanism — Camacho-Pereira J, et al., Cell Metabolism (2016)

   Links rising CD38 NADase activity to age-related NAD+ decline (animal/cell data).

5. 05
   NAD+ precursor supplementation in human ageing: clinical evidence and challenges — Vinten KT, Houtkooper RH, et al., Nature Metabolism (2025)

   Recent review concluding human anti-ageing efficacy remains limited despite reliable NAD+ elevation.

6. 06
   PubMed search: NAD+ precursor supplementation human clinical trial aging — Various, PubMed (2026)

   Live search of the human trial literature on NAD+ and its precursors.