What is NAD+?

This guide explains what NAD+ is, what it does in the body and what human research has and has not shown, using primary sources only.

We are an independent guide: we do not provide, sell or arrange treatment, and nothing here is a recommendation.

What is NAD+?

NAD+ (nicotinamide adenine dinucleotide) is a coenzyme found in cells, which means a helper molecule that enzymes work with.

A review in Nature Reviews Molecular Cell Biology describes it as “a coenzyme for redox reactions, making it central to energy metabolism” ¹.

Whether adding more NAD+ from outside the body has any health effect is a separate question, and most of this page is about that gap between the chemistry and the claims.

What does NAD+ do in the body?

NAD+ works as a coenzyme in energy metabolism and as a cofactor for enzymes involved in DNA repair and cell signalling ¹.

Those enzymes include the sirtuins, CD38 and the PARP family ¹.

This is basic biochemistry and it is well established.

It describes what NAD+ does inside cells; it does not show that raising NAD+ with an injection, drip or supplement changes your health.

Is NAD+ a vitamin?

No: NAD+ is a coenzyme, while niacin (vitamin B3) is the dietary vitamin in the same chemical family.

The NHS says there are two forms of niacin, nicotinic acid and nicotinamide, both found in food, and that you should be able to get all the niacin you need from your daily diet ².

Research papers describe those two forms as dietary precursors for NAD+ ³.

When we searched the NHS website for NAD+ on 11 November 2026, it returned no results ⁴.

So “NAD vitamin” is a loose phrase: the vitamin is niacin, and NAD+ is a separate molecule.

Do NAD+ levels change with age?

It depends on the tissue and the study: some human studies report lower NAD+ with age, and a 2026 study found whole-blood NAD+ stable.

The table summarises five human studies; each compared different groups of people rather than following the same people over time.

Sample	Study	What it reported	Design
Skin (49 people, ages 0-77, taken during unrelated surgery)	Massudi et al., 2012	Lower NAD+ with increasing age in both sexes 5	Cross-sectional
Brain (MR spectroscopy, healthy volunteers)	Zhu et al., 2015	Lower NAD+ with age 6	Cross-sectional imaging
Blood plasma (healthy people aged 20-87)	Clement et al., 2019	Lower plasma NAD+ with age 7	Cross-sectional
Skeletal muscle	Janssens et al., 2022	Lower in older adults, closer to younger levels in exercise-trained older adults 8	Cross-sectional
Whole blood (seven cohorts)	Trętowicz et al., 2026	Remained stable with age 9	Multi-cohort measurement

Plasma, whole blood and the inside of cells are different measurements, so the results are not directly comparable ⁷.

A 2025 review in Nature Metabolism concluded that an age-related decline in NAD+ has been consistently observed in humans “only in a limited number of studies” ¹⁰.

An earlier review in Experimental Gerontology made the same point: human data are limited ¹¹.

Even where levels are lower, whether that matters for health, or whether restoring them would help, is not something these studies were designed to show.

What are NAD+ precursors such as NMN and NR?

Precursors are NAD+ intermediates, and nicotinamide riboside (NR) and nicotinamide mononucleotide (NMN) are the two that have been studied most ¹².

They are different molecules from NAD+ itself, and the human trials of NR and NMN cited on this page gave them by mouth.

A 2026 systematic review found that oral NR and NMN consistently raised NAD-related measures in blood or cells and were generally well tolerated over weeks to months ¹³.

Two trials show what raising a measure looks like in practice: a 6-week crossover trial found oral NR was well tolerated and raised NAD+ in healthy middle-aged and older adults ¹⁴.

In 12 aged men, 1 g a day of oral NR for 21 days raised the skeletal-muscle NAD+ metabolome without changing mitochondrial bioenergetics ¹⁵.

A higher NAD+ measure is a chemical result, and it is a separate matter from whether anyone feels or does better.

Our comparison of NMN vs NAD+ covers how each is taken and what each has been tested for.

What does the research show in people?

The human research on NAD+ itself is small and mostly measures chemistry rather than health, and a 2026 systematic review found no outcomes trials of intravenous or intramuscular NAD+ for ageing or wellness ¹³.

That review identified 113 eligible studies: 33 in humans (28 of them randomised) and 80 in rodents ¹³.

Its overall conclusion was that NAD+ augmentation “shows clear biological activity” but that clinical effectiveness for ageing or wellness outcomes “remains inconclusive” ¹³.

The main published human study of infused NAD+ we found is a pilot in 11 healthy men, of whom 8 received NAD+ and 3 received saline ¹⁶.

The dose was 750 mg over 6 hours, and the study measured blood and urine chemistry, not symptoms or health outcomes ¹⁶.

The authors wrote that no data had existed on the fate of directly infused NAD+ in people before their study ¹⁷.

What they saw was a metabolite profile consistent with NAD+-degrading enzyme activity, so NAD+ was not simply delivered unchanged ¹⁷.

At the study’s infusion rate, NAD+ was “rapidly and completely removed from the plasma” for at least the first two hours, which is a result about where it goes, not about any benefit ¹⁷.

For oral precursors, the same systematic review found that effects on functional, metabolic and vascular outcomes were “heterogeneous and often null or endpoint-specific” ¹³.

Our guide to what the evidence says about benefits goes through each claimed use one by one.

How are NAD+ products taken?

NAD+ and its precursors are taken by mouth (precursors), by drip into a vein, or by injection into a muscle or under the skin, and the evidence differs sharply by route.

Route	What the research we found says
Oral precursors (NR, NMN)	Most human trials; raised NAD-related measures; health outcomes mixed 13
NAD+ by IV infusion (a drip)	A small pilot and small uncontrolled reports; a 2026 review calls the evidence “preliminary and insufficient to support routine clinical or wellness use” 18
NAD+ by intramuscular or subcutaneous injection	No eligible outcomes trials for intramuscular NAD+ 13; our PubMed searches on 11 November 2026 found no human studies of subcutaneous NAD+

We cover the clinic routes in NAD+ injections and NAD+ IV therapy.

How an injected or infused product is classified affects who may supply and advertise it, which we set out under legal status in the UK.

Where can I read the primary research?

Every study named on this page is in the sources list below, with a link to its PubMed record, publisher page or regulator page.

Three reviews are good starting points: the 2026 systematic review in Ageing Research Reviews ¹³, the 2026 narrative review of IV NAD+ in Frontiers in Aging ¹⁸ and the 2025 review in Nature Metabolism ¹⁰.

We also searched NICE for NAD+ on 11 November 2026 and found no NICE guidance on it ¹⁹.

If you want a clinician’s view of any of this, your GP or pharmacist is the right place to start.

This page is general information, not medical advice. Speak to your GP or a registered prescriber before deciding anything about NAD+ or any supplement, injection or infusion, and read our medical disclaimer.

It was drafted with AI assistance from a fact-pack of primary sources by the NAD Injections editorial team and has not been clinically reviewed.