Do NAD+ Supplements Actually Work? The Science and Where I Stand
Last updated: September 2026
NAD+ has travelled a remarkable distance in twenty years, from a molecule almost nobody outside biochemistry had heard of to the centre of the longevity conversation. Patients in my clinic in Hale ask me about it constantly, usually having read something very confident online and spent a considerable sum on the strength of it.
The underlying science is genuinely interesting, and the hundred-year story of how we came to understand it is better than the marketing version. But the supplement market has run a long way ahead of the evidence, and a surprising amount of what is sold to UK buyers is not actually authorised for sale here at all.
This article covers the real history, what NAD+ does, what the human trials have and have not measured, the UK legal position, and where I stand on recommending any of it. I should say at the outset that I do not stock or sell any NAD supplement and have no commercial relationship with any manufacturer.
Important context: supplements are foods, not medicines. This article is educational. It is not personalised medical advice and it is not a substitute for a conversation with your own GP or pharmacist, particularly if you take regular medication.
Key Takeaways
| Question | Short answer |
|---|---|
| What is NAD+? | A coenzyme present in every living cell, central to energy metabolism and to several repair and signalling enzymes |
| Does it fall with age? | The weight of evidence says yes across multiple tissues, though how much varies considerably between studies |
| Can you swallow NAD+ directly? | Not usefully. Supplements supply precursors the body converts |
| Do supplements raise NAD+ in humans? | Several have been shown to, in blood, in short trials |
| Does raising it make you healthier? | Not demonstrated. The trials measured biomarkers, not how people feel or function |
| Is NMN legal in the UK? | No. It is not an authorised novel food in Great Britain, despite being widely sold online |
| What about NAD IV drips? | Expensive, invasive, and the outcome evidence is weaker still |
| Do I recommend one? | No. Not because they are harmful, but because nobody has yet shown the benefit is real |
In This Article
- Where NAD+ came from: beer, pellagra and a hundred years of research
- What NAD+ actually does in the body
- Does NAD+ really decline with age?
- The mouse studies that started the boom
- Why supplements use precursors rather than NAD+ itself
- What the human trials have actually measured
- The UK legal position, and why it matters to you
- Where I stand on recommending a NAD supplement
- What would change my mind
- NAD supplements versus IV drips
- What to check if you decide to buy anyway
- What can and cannot legally be claimed
- Who should be cautious
Where NAD+ Came From: Beer, Pellagra and a Hundred Years of Research
The story begins, improbably, with brewing.
In the early 1900s, scientists studying how yeast converts sugar into alcohol noticed something odd. Certain enzymes simply would not work unless an unidentified "helper" substance was present in the mixture. Remove it and fermentation stopped. That helper was eventually identified as nicotinamide adenine dinucleotide, NAD.
The picture sharpened in the 1930s and 1940s, and it did so through a public health tragedy rather than a laboratory triumph.
Pellagra was a devastating condition affecting the skin, gut and nervous system, and it killed tens of thousands of people in the American South in the early twentieth century. It was long assumed to be infectious. It was eventually shown to be a deficiency disease, caused by inadequate vitamin B3, or niacin. Researchers then worked out that the body uses B3-derived compounds as the raw material to build NAD+.
That connected three things for the first time: a dietary vitamin, a coenzyme found in every cell, and a serious human disease. It placed NAD firmly at the centre of metabolism.
For the next fifty years, NAD+ was regarded as a workhorse. Essential, ubiquitous, and not particularly exciting. What changed was the gradual realisation that it was doing considerably more than moving electrons around.
What NAD+ Actually Does in the Body
NAD+ exists in every living cell and performs several distinct jobs.
| Function | What it involves |
|---|---|
| Energy metabolism | NAD+ shuttles electrons through the reactions that convert food into ATP inside mitochondria. This is its original and best-understood role |
| Sirtuin activity | Sirtuins are a family of proteins involved in stress resistance and metabolic regulation. They cannot function without NAD+ |
| DNA damage response | PARP enzymes, which detect and respond to DNA damage, consume NAD+ as they work |
| Cellular signalling | NAD+ and its metabolites take part in signalling relevant to immune and inflammatory pathways |
Two features of that list are what made NAD+ interesting to ageing researchers, and they are worth understanding because they explain the entire hypothesis.
First, NAD+ is consumed, not merely used. Sirtuins and PARPs break it down as part of doing their job, so the body has to keep regenerating it through recycling, known as the salvage pathway. Supply is therefore a genuine constraint rather than a theoretical one.
Second, the same molecule sits at the junction of energy production and damage repair. If availability is limited, those two essential processes are effectively competing for it. That is an elegant explanation for why cells might become less resilient over time.
Elegance is exactly what makes a hypothesis attractive long before it has been properly tested in people. That is the position we are still in.
Does NAD+ Really Decline With Age?
This is presented as settled fact in almost all supplement marketing, so it is worth being precise about.
The weight of evidence does support a decline. It has been observed across multiple tissues and in several different types of study, and it is a reasonable basis for scientific interest.
But the picture is less uniform than the advertising suggests. The magnitude varies substantially between studies, between tissues and with the measurement method used. Measuring NAD+ reliably in living human tissue is technically difficult, and a good deal of the human data is indirect.
A fair summary: NAD+ availability appears to fall with age, the effect is real, and the size of it is not settled. That justifies research. It does not, on its own, justify a purchase.
The Mouse Studies That Started the Boom
Public interest accelerated sharply after a run of high-profile animal studies, several of them associated with the Harvard laboratory of David Sinclair.
In the most widely discussed experiments, older mice were given NMN, a direct precursor the body uses to build NAD+. Researchers observed improvements in mitochondrial function, cellular energy markers and various biochemical features associated with ageing.
The genuinely important conclusion was conceptual rather than practical. It suggested that some ageing-related cellular changes are dynamic rather than fixed, which was a real shift in how the field thought about ageing. It did not make old mice young, and it was never claimed to.
Three things are worth holding onto whenever you read about this research:
- Mice are not small people. A very long list of interventions that rejuvenate mice do nothing measurable in humans. This is the single most reliable pattern in the whole of ageing research
- Laboratory mice are genetically uniform and live in identical conditions. Human ageing is shaped by genetics, sleep, nutrition, activity, stress and circumstance, none of which is standardised
- Cellular markers are not outcomes. A mouse with better mitochondrial markers has not been shown to live longer or better on that basis alone
Why Supplements Use Precursors Rather Than NAD+ Itself
You cannot usefully swallow NAD+. It is a large, unstable molecule that is broken down during digestion rather than absorbed intact and delivered to cells. Any product claiming to give you "NAD+ directly" in a capsule is misunderstanding its own ingredient.
So supplements supply precursors: building blocks the body converts through established biochemical pathways.
| Precursor | What it is | UK status as a food supplement |
|---|---|---|
| Niacin (nicotinic acid) | The original form of vitamin B3, the one identified through pellagra research | Long established. Permitted |
| Nicotinamide (NAM) | The amide form of vitamin B3, used directly in the salvage pathway | Long established. Permitted |
| Nicotinamide riboside (NR) | A newer precursor, assessed by EFSA in 2019 | Authorised as a novel food, from approved sources |
| Nicotinamide mononucleotide (NMN) | The precursor used in most of the famous mouse work | Not authorised in Great Britain. See the legal section below |
What the Human Trials Have Actually Measured
This is the section I most want you to read, because it is the difference between an informed purchase and an expensive hope.
There are now a number of human trials of oral NAD precursors, and some are properly designed. They generally show what they set out to show: that you can raise NAD-related measures in blood. That is a real finding and not a trivial one, because a supplement that did nothing detectable would be worse.
The best-evidenced example in the UK market is a double-blind, randomised, placebo-controlled crossover trial published in npj Aging in 2024, testing a combination formulation in 26 participants aged 20 to 80, over 28 days per arm with a 28-day washout. It reported a mean rise of 26.5% in whole blood NAD+ at week four, alongside changes in SIRT1, NAMPT, some inflammatory markers and protein glycation. That is a considerably better standard of evidence than most of this category can point to.
Now look carefully at what was measured. In that trial and in the human literature generally, the outcomes are overwhelmingly biomarkers: the concentration of NAD+ in blood, levels of related enzymes, inflammatory signalling molecules, markers of protein glycation, and in some cases estimates of "biological age" derived from molecular patterns.
What has largely not been measured, in properly powered trials of meaningful duration:
- Whether people actually have more energy
- Whether fatigue improves on a validated scale
- Whether physical function, strength or endurance changes
- Whether cognition changes
- Whether anyone lives longer, or in better health
A supplement that raises a number in a blood sample has demonstrated that it does something. It has not demonstrated that the something is worth having. Those are different claims, and only the first one currently has evidence behind it.
A note on "biological age"
Several trials report reductions in "biological age" derived from molecular patterns such as antibody glycosylation. These are interesting research tools. They are not validated clinical outcomes, different methods give different answers, and a reduction in one of them has never been shown to correspond to living longer or in better health.
Treat any number of this kind as a laboratory measurement rather than a fact about your life. If someone tells you a capsule made them two years younger, what they mean is that a molecular index shifted, and nobody yet knows what that index is worth.
Why trials in this field tend to be small and short
Supplement companies fund most of this research, and there is no patent-protected blockbuster at the end of it to justify a thousand-participant multi-year study. So trials are typically a few dozen people over four to twelve weeks.
That design is entirely appropriate for establishing that a compound does something measurable. It is structurally incapable of establishing that the something matters, because the outcomes people care about take longer than twelve weeks to change and need far more participants to detect.
The UK Legal Position, and Why It Matters to You
This is the practical consumer protection part, and it is what I would most like people to know before ordering anything.
NMN is not an authorised novel food in Great Britain. It sits on the Food Standards Agency's novel food catalogue as requiring authorisation, applications have been submitted, and as things stand no NMN product has completed the process. The position in the EU is the same.
NMN is nevertheless sold extensively to UK consumers, largely through overseas websites and online marketplaces. If you have bought an NMN supplement online, there is a reasonable chance you have bought something that is not authorised for sale as a food in this country.
Why that matters practically, beyond the legality:
- Novel food authorisation is a safety assessment. Skipping it does not make a product dangerous, but it does mean no independent body has assessed it
- Unauthorised products sit outside UK manufacturing oversight, so content, purity and dose are whatever the seller says they are
- Independent testing of NMN products has repeatedly found content varying widely from label. That is the predictable consequence of a market without regulatory scrutiny
- You have very little recourse if something is wrong
Nicotinamide riboside, by contrast, was assessed by EFSA in 2019 and is authorised from approved sources. Niacin and nicotinamide are long-established nutrients with no such question hanging over them.
If a NAD supplement's headline ingredient is NMN and it is being shipped to you in the UK, the first question is not whether it works. It is whether it is legally allowed to be sold to you at all.
Where I Stand on Recommending a NAD Supplement
People ask me which one to buy. They are usually surprised by the answer, so let me give the reasoning rather than just the conclusion.
I do not currently recommend any NAD supplement.
I want to be clear about what that is and is not saying, because this is a field where people talk past each other.
It is not that the products are harmful. The formulations that have been studied appear reasonably well tolerated over the periods tested. It is not that the companies are dishonest. Some of them are doing serious work, publishing in peer-reviewed journals and collaborating with universities, which is more than most of the supplement industry attempts. It is not that the biology is nonsense. The NAD hypothesis is one of the more interesting ideas in ageing research and I follow it with genuine curiosity.
The problem is the gap between what has been shown and what is being sold.
| What the human trials have shown | What they have not shown |
|---|---|
| Oral precursors can raise NAD+ concentration in blood, by meaningful percentages, over a few weeks | That anyone had more energy |
| Related markers move in a coherent direction: enzymes, some inflammatory signals, glycation measures | That fatigue improved on a validated scale |
| The formulations are reasonably well tolerated over short periods | That physical function, strength or endurance changed |
| Research-tool estimates of "biological age" shifted in some studies | That cognition changed |
| The underlying biology is plausible and worth studying further | That anyone lived longer, or in better health |
Here is the part that matters. Even the best-evidenced product in this category has not cleared that second column. Its trial was well designed and it still enrolled 26 people for 28 days and measured only biomarkers. If the strongest case available does not demonstrate a benefit anyone would notice, the weaker cases certainly do not.
When I recommend something to a patient, I am making an implicit promise: that the benefit is real and that it is likely to be worth what it costs you. On the current evidence I cannot make that promise about any NAD supplement. I would rather say so plainly than let my professional opinion do work that the data cannot do.
There is a specific reason a doctor's recommendation carries weight here, and it is the reason I am being careful. If a friend tells you a supplement is worth trying, you weigh it as one person's experience. If a doctor tells you, you reasonably assume there is evidence behind it. Borrowing that credibility for something the evidence does not yet support is how patients end up spending money they should have kept.
What Would Change My Mind
This is not a closed door, and I would genuinely like to be proved wrong. I would look again seriously at:
| What I would need to see | Why it matters |
|---|---|
| Several hundred participants, not a few dozen | Small trials cannot reliably detect modest real effects, and they overstate the ones they do find |
| A duration measured in months, ideally a year or more | The outcomes that matter do not change in four weeks |
| A pre-registered primary endpoint that is a functional outcome | Fatigue on a validated scale, grip strength, walking speed, cognitive testing. Something a person would notice |
| Independent replication | By a group with no commercial relationship to the product |
| Results that hold when the analysts have no financial interest | Manufacturer-funded research is normal and not disqualifying, but independent confirmation is what turns a finding into a fact |
None of that is an unreasonable bar. It is the ordinary standard we apply to anything we expect people to take every day for years. If a NAD product clears it, I will say so here and I will rewrite this article.
What I Would Do With the Same Money
A year of a premium NAD supplement typically costs several hundred pounds. For the same outlay, or considerably less:
- Strength training twice a week. Better evidence for healthy ageing than anything currently available in a capsule, and a set of dumbbells is a one-off cost
- Daily broad spectrum sun protection. The single best-evidenced anti-ageing intervention for skin, at a fraction of the price
- Getting persistent fatigue properly investigated by your GP. Free, and it occasionally finds something that genuinely matters
- Addressing sleep. Free, deeply unglamorous, and the lever most people have never actually pulled
If all of that is already in place and you want to try something speculative with money you are comfortable losing, that is a perfectly reasonable adult decision and I am not going to lecture you about it. Just make it knowing it is speculative, and buy something that is legally authorised for sale here.
NAD Supplements Versus IV Drips
NAD infusions have become heavily marketed, particularly in aesthetic and wellness settings, and they are expensive.
My view, plainly: the outcome evidence for NAD IV infusions is considerably weaker than the marketing around them, especially where claims involve detoxification, rapid rejuvenation or dramatic energy restoration. Regulators have raised concerns about unsubstantiated claims in this area. Infusions are also invasive, carry the risks that any infusion carries, and are frequently unpleasant to receive.
Oral precursors at least work with the body's own machinery, cost a fraction as much, and have a clearer base of published human research behind them, such as it is. If the evidence for the cheap daily option is still preliminary, the case for the expensive invasive one is weaker still.
I do not offer NAD infusions and I have no plans to.
What to Check If You Decide to Buy Anyway
Plenty of people will read all of the above and want to try one regardless. That is a legitimate choice with your own money. If you are going to, these are the checks I would apply, in this order.
| Check | What good looks like | What should worry you |
|---|---|---|
| Is the ingredient authorised for sale in GB? | Niacin, nicotinamide, or NR from an approved source | NMN as the headline ingredient, shipped from overseas |
| Is there human trial data on this product? | A published, peer-reviewed, placebo-controlled trial of the actual formulation | Citations to mouse studies, or to trials of a completely different ingredient |
| Who ran and funded the trial? | Stated openly, ideally with academic collaboration | Not disclosed anywhere. Manufacturer involvement is normal, but it must be visible |
| What did the trial actually measure? | Clear about whether outcomes were biomarkers or how people felt and functioned | "Clinically proven", with no indication of what was proven |
| Is the full formulation disclosed? | Every ingredient with its dose | "Proprietary blend", which exists to conceal how little of the expensive ingredient is present |
| What claims are being made? | Restrained, specific, using authorised wording | Reversing ageing, detoxifying, curing fatigue, adding years to your life |
| Is there third-party testing? | Independent verification of content and purity | No testing information anywhere on the site |
| Does a doctor's face appear beside a health claim? | Factual information, no personal endorsement | An advertiser willing to break the rules on health claims is telling you how it treats every other rule |
| What does it cost per day, honestly? | A figure you would still be comfortable with in twelve months | A subscription you will forget about. This is a long-game purchase or it is nothing |
What Can and Cannot Legally Be Claimed
Worth understanding, because it tells you how to read every supplement advertisement you will ever see.
In the UK, only health claims on the GB Nutrition and Health Claims Register may be used in advertising a food or supplement. The register is specific, the wording is prescribed, and a product must contain a defined minimum amount of the nutrient to use a claim at all.
For vitamin B3, the authorised claims include:
- Niacin contributes to normal energy-yielding metabolism
- Niacin contributes to the reduction of tiredness and fatigue
- Niacin contributes to the normal functioning of the nervous system
- Niacin contributes to normal psychological function
- Niacin contributes to the maintenance of normal skin and mucous membranes
Those are the permitted statements. Anything about longevity, reversing ageing, biological age, DNA repair or cellular rejuvenation is not authorised and cannot lawfully be claimed for a product, whatever any study found.
There is also a specific rule worth knowing about, because it explains why you will not find a doctor's endorsement on this page. Health claims that reference the recommendation of an individual doctor or health professional are prohibited for foods and supplements. It exists precisely because a clinician's endorsement carries weight the evidence may not.
This is a useful filter. When you see a supplement advertised with grand claims about ageing, or with a doctor's personal endorsement attached, you are not looking at a product with better evidence. You are looking at an advertiser who has decided the rules do not apply to them.
Foundations First
A supplement sits on top of the basics or it does very little. If the foundations are not in place, no capsule compensates.
| Foundation | Practical version |
|---|---|
| Sleep | A consistent wake time is usually the biggest single lever, and the one most people have never actually tried |
| Movement | Regular counts for more than intense. Brisk walking is genuine exercise |
| Strength | Resistance work twice a week, particularly from midlife onwards |
| Nutrition | Adequate protein, plenty of fibre, a wide range of plants. Unglamorous and effective |
| Alcohol | Less. Consistently the least welcome item on any list of this kind |
| Stress and connection | Harder to action, and measurably matters |
If someone asked me to choose between a year of a NAD supplement and a year of consistent sleep and strength training, the answer would not be close, and it would not be the supplement.
Who Should Be Cautious
- If you are pregnant or breastfeeding. Supplements of this kind have not been assessed for pregnancy
- If you are under active oncology care. Discuss any supplement with your oncology team first, without exception
- If you take regular medication. Check with your GP or pharmacist for interactions
- If you have liver or kidney disease, or any complex medical condition
- Where high-dose niacin is involved, which can cause flushing and, at higher doses, affect liver function and glucose control
- If you already take several supplements. Overlapping B vitamins across multiple products add up without anyone noticing
Always tell your GP what supplements you take. Most people do not, and it is exactly the sort of thing that matters when something else goes wrong.
What I Can and Cannot Help With
| What this clinic does | What belongs with your GP |
|---|---|
| Explaining what the evidence for something does and does not show | Investigating fatigue, low energy or feeling run down |
| Cosmetic treatments and skin quality | Blood tests, deficiency screening and diagnosis |
| Helping you avoid spending money on things without evidence | Reviewing interactions with your medication |
| Being honest about how thin the evidence still is | Any symptom that needs a cause found |
If you feel persistently exhausted, please see your GP rather than reaching for a supplement. Fatigue has a long list of treatable causes, several of them common, and none of them is diagnosed by buying capsules.
Frequently Asked Questions
Do NAD+ supplements actually work?
They can raise NAD+ levels in blood, which is a real and measurable effect. Whether that produces any benefit you would notice has not been demonstrated in a properly powered trial of meaningful duration, for any product.
What does NAD+ stand for?
Nicotinamide adenine dinucleotide. It is a coenzyme found in every living cell, central to energy metabolism and used by enzymes involved in signalling and the DNA damage response.
Why does NAD+ decline with age?
Probably a combination of reduced recycling capacity and increased consumption by repair and inflammatory enzymes. The decline is supported across multiple tissues, though its size varies between studies.
Can you take NAD+ directly?
Not usefully. It is broken down in digestion. Supplements supply precursors the body converts instead.
Is NMN legal in the UK?
No. NMN is not an authorised novel food in Great Britain and no product has completed the authorisation process. It is nevertheless sold widely online, mostly from overseas.
Is nicotinamide riboside legal in the UK?
Yes, from approved sources. It was assessed by EFSA in 2019 and carries novel food authorisation.
Do NAD supplements give you more energy?
No trial has properly demonstrated that. Human studies have measured NAD+ in blood and related markers, not energy or fatigue on validated scales. The authorised wording for vitamin B3 refers to its contribution to normal energy-yielding metabolism, which is a statement about biochemistry rather than about how you will feel.
Are NAD IV drips better than capsules?
There is no good evidence that they are, and considerably less published human research behind them. They are also far more expensive and carry the risks of any infusion.
Which brand do you recommend?
None, currently. I do not stock or sell any NAD supplement and have no commercial relationship with any manufacturer. If the evidence improves to the standard set out above, I will update this article and say so.
How long would I need to take one to know if it works?
Honestly, you may not be able to tell at all, because the measured effects are things you cannot feel. If you try one, decide in advance what would count as a result, or you will simply keep paying indefinitely.
Should I get my NAD+ level tested?
There is no established clinical test, no reference range, and no action that would sensibly follow from a result. I would not spend money on it.
What should I spend the money on instead?
Sleep is free. Strength training is nearly free. If you want to spend specifically on your skin, daily sun protection outperforms every supplement on the market at a fraction of the cost.
Related Reading
- Which Supplements Are Worth Taking for Skin, Strength and Healthy Ageing
- Do Collagen Supplements Work?
- Glycation: Is Sugar Ageing Your Skin?
- IV Peptides: An Honest Opinion
- Collagen Banking: The Long Game Approach to Ageing Well
- Treatments at Dr Caroline Warden Clinic
References
- Henderson JD, Quigley SNZ, Chachra SS, Conlon N, Ford D. The use of a systems approach to increase NAD+ in human participants. npj Aging. 2024;10:7.
- Covarrubias AJ, Perrone R, Grozio A, Verdin E. NAD+ metabolism and its roles in cellular processes during ageing. Nat Rev Mol Cell Biol. 2021;22(2):119-141.
- Food Standards Agency. Novel foods: guidance and authorisation.
- Department of Health and Social Care. Great Britain Nutrition and Health Claims (NHC) Register.
- ASA/CAP. Food: health claims.
- NHS. B vitamins and folic acid.
About the Author
Dr Caroline Warden is a practising NHS GP and aesthetic doctor with nearly twenty years of clinical experience, an independent prescriber, and holder of a Level 7 postgraduate diploma in cosmetic injectables. She is Medical Director and sole practitioner at Dr Caroline Warden Skin & Aesthetic Clinic, 2 Crown Passages, Hale, Altrincham, a family-run clinic she runs with her sister Louise, seeing patients from Hale, Hale Barns, Bowdon, Altrincham, Timperley, Sale, Alderley Edge, Wilmslow, Knutsford and across Cheshire and South Manchester. She holds no commercial relationship with any supplement manufacturer. GMC number 6157708.
