NADH: What It Does, the Evidence, and How It Differs from NR

Your cells have spent your entire life producing energy with a molecule you have probably never heard of: NADH. It is the active, reduced form of NAD+, the central coenzyme of cellular energy metabolism, and without it the production of ATP—the energy currency of every cell in your body—simply grinds to a halt. As a supplement, NADH has been studied mainly in the context of chronic fatigue and cognitive performance. The available studies are limited in sample size, but some clinical trials in humans show reductions in perceived fatigue at doses of 10–20 mg/day. This guide reviews the available evidence, the mechanism of action, and why NAD+ precursors such as NR (nicotinamide riboside) have displaced NADH in next-generation formulations.

What is NADH and what does it do?

NADH works primarily as an electron carrier in the mitochondrial respiratory chain: it is the molecule that supplies energy to produce ATP, the energy currency of every cell in the body.

NADH is the reduced form of NAD+ (nicotinamide adenine dinucleotide), a coenzyme present in all cells. In biochemical terms, NADH donates its electrons to Complex I of the electron transport chain, which drives ATP synthesis. Without functional NADH, cellular energy production is compromised. This direct link to energy metabolism is the basis for its use as a supplement.

As an oral food supplement, NADH is commonly marketed in the form of ENADA® (stabilized NADH), at doses ranging from 5 mg to 20 mg per serving. The underlying hypothesis is that increasing the availability of exogenous NADH could raise intracellular NAD+ levels and, in doing so, support energy production in tissues with high metabolic demand, such as the brain and muscle.

What is the difference between NADH and NAD+?

NAD+ and NADH are two sides of the same coenzyme: NAD+ is the oxidized form (it accepts electrons) and NADH is the reduced form (it donates them). In cellular metabolism, the NAD+/NADH cycle runs continuously. Aging is associated with a progressive decline in total NAD+ levels, which has driven research into supplements that restore this pool. If you want to dig deeper into what NAD+ is and how it influences health, we cover it in detail in that guide.

Mechanism of action: how NADH works in the cell

NADH acts as an electron carrier in the mitochondrion, but its effectiveness as an oral supplement depends on how much of it reaches the cell intact: oral bioavailability is its main limitation.

Absorption and bioavailability

Oral NADH faces a significant challenge: it is a relatively large molecule and unstable in the acidic environment of the stomach. Stabilized formulations (such as ENADA®) use enteric coatings to protect it until it reaches the small intestine, where it is partially absorbed. The oral bioavailability of NADH is limited because of its instability in the acidic gastric environment and its larger molecular size. By contrast, precursors such as NR have shown efficient oral absorption in humans, with documented increases in blood NAD+ (Trammell et al., 2016; Martens et al., 2018).

Intracellular pathway

Once absorbed, NADH can contribute to the intracellular NAD+ pool through the nicotinamide salvage pathway. However, research suggests that most exogenous NADH does not enter the mitochondrion directly but is instead metabolized in the cytoplasm. The mitochondrion has its own pathways for synthesizing NADH from precursors such as tryptophan, niacin, NMN and NR.

Its role in ATP production

In the mitochondrion, each molecule of endogenous NADH donates electrons to Complex I, generating roughly 2.5 molecules of ATP. This is the physiological mechanism that underpins the rationale for supplemental NADH, although—as explained below—oral NADH does not reach the mitochondrion directly, which limits its efficiency as an energy precursor.

Why is NR more efficient as an NAD+ precursor?

NR (nicotinamide riboside) enters the NAD+ salvage pathway directly and more efficiently than oral NADH. A clinical trial in 24 middle-aged and older adults (55–79 years) showed that 1,000 mg/day of NR over 6 weeks raised blood NAD+ levels by 60% compared with placebo. It is worth noting that this dose (1,000 mg/day) is higher than the maximum authorized as a novel food in the EU for NR chloride (300 mg/day, EU Reg. 2022/1160). Research into the comparative pharmacokinetics of the various NAD+ precursors remains active.

Clinical evidence: what the studies say about NADH

Clinical research on NADH as a supplement is more limited than that on other NAD+ precursors. The available studies have focused mainly on three areas: chronic fatigue syndrome (CFS), cognitive performance and fatigue in the context of jet lag.

Chronic fatigue syndrome (CFS)

The most frequently cited trial is Forsyth et al. (1999), a double-blind crossover study in 26 patients with CFS who received 10 mg/day of stabilized NADH (ENADA®) for 4 weeks. In the NADH group, 31% of participants reported an improvement in fatigue versus 8% in the placebo group (p < 0.05). The limitations are clear: a small sample, a crossover design with a short washout period and subjective outcome measures.

The Santaella et al. (2004) study, in 31 patients with CFS, compared oral NADH as monotherapy with conventional therapy and documented a reduction in symptoms during the first months of treatment, although the difference was not maintained in later periods. Along different lines, subsequent trials by Castro-Marrero et al. (2021) combined NADH with CoQ10 (200 mg) for 8 weeks and observed changes on the fatigue scale and in markers of oxidative stress; because this was a combination, the effects cannot be attributed to NADH alone. Each ingredient has been studied individually in other contexts; the specific combination in that formula has not been the subject of its own clinical trial with an adequate control group.

Cognitive performance and jet lag

Possible effects of NADH on attention and cognitive performance under sleep deprivation have been explored, although the available evidence is very limited and does not allow firm conclusions to be drawn.

Summary table of clinical evidence

A key limitation of the evidence

None of the available studies exceeds 50 participants. Most are pilot or phase I/II studies. There are no high-quality meta-analyses on oral NADH in healthy populations. The current evidence is insufficient to establish claims of clinical benefit in the general population. The data suggest potential in specific contexts of pathological fatigue, but they do not allow for generalization.

Investigated applications of NADH as a supplement

Based on the available evidence, NADH as a supplement has been investigated in the following contexts. It is worth distinguishing between what the studies have measured and what can be stated as an observed outcome. For a complementary overview, we have compiled the benefits and uses of NADH in a separate guide.

Chronic fatigue syndrome (CFS/ME)

This is the area with the most support in the literature. The studies by Forsyth et al. (1999) and Santaella et al. (2004) suggest that NADH could help reduce perceived fatigue in patients with CFS, although the evidence is preliminary and the sample sizes are small. It cannot be claimed that NADH “treats” CFS.

Cognitive performance and attention

Possible effects of NADH on attention under sleep deprivation have been explored. These results are preliminary and cannot be extrapolated to everyday conditions without further research.

Neurological research: context and limitations

Some researchers have explored the role of NAD+ in neuronal function. Birkmayer et al. (1993) administered NADH intravenously—not orally—to patients with Parkinson’s disease and observed changes in motor parameters. This route of administration is radically different from oral supplementation, and the results cannot be extrapolated. There are no methodologically robust clinical trials of oral NADH for this indication. In the more than 30 years since that initial study, no controlled clinical trials have been published that replicate these results with oral NADH. This line of research is experimental in nature and does not provide a basis for the use of oral NADH in any neurological condition.

Oral NADH is not indicated for the treatment or prevention of any neurological disease.

Does NADH help with energy in healthy people?

The honest answer is: the evidence in healthy people with no underlying condition is very limited. The available studies have been carried out mainly in populations with pathological fatigue or under conditions of acute stress (sleep deprivation). There are no robust clinical trials demonstrating improvements in perceived energy in healthy adults with normal NAD+ levels.

Niacin (vitamin B3), from which NAD+ is derived, does have EFSA-authorized claims for “contributing to normal energy-yielding metabolism” and “reducing tiredness and fatigue” (EU Regulation 432/2012). These claims apply to niacin as a nutrient, not to NADH as a specific supplement.

NADH dosage: what the studies have used

The available clinical studies have used NADH doses ranging from 5 mg to 20 mg per day. The most frequently investigated dose is 10 mg/day in a stabilized formulation (ENADA®).

Doses by research context:

• Chronic fatigue syndrome: 10 mg/day (Forsyth et al., 1999; Santaella et al., 2004)
• Cognitive performance / sleep deprivation: 20 mg/day (limited evidence)
• Intravenous administration (Parkinson’s): variable doses; a route radically different from oral and not extrapolable to supplementation

Form of administration

Oral NADH formulations are usually presented as sublingual or enteric-coated tablets to protect the molecule from gastric acid. Sublingual absorption avoids first-pass hepatic metabolism and may favor bioavailability, although comparative data are scarce.

When to take it

Studies have generally administered NADH on an empty stomach, in the morning, to maximize absorption. There are no solid data on the difference between taking it with or without food.

Important: the doses used in the studies are informational. They do not constitute a usage recommendation. Always consult your doctor or pharmacist before adding any supplement to your routine, especially if you take medication or have pre-existing health conditions.

Why has research on NAD+ precursors shifted toward NR?

The accumulated pharmacokinetic evidence shows that NR (nicotinamide riboside) raises blood NAD+ levels more efficiently than oral NADH. A clinical trial in 24 middle-aged and older adults (55–79 years) documented a 60% increase in whole-blood NAD+ with 1,000 mg/day of NR over 6 weeks.

Two important caveats about this figure: the dose in the study (1,000 mg/day) is higher than the maximum authorized as a novel food in the EU for NR chloride (300 mg/day, EU Reg. 2022/1160), and the documented increase corresponds to whole-blood NAD+, not necessarily across all tissues.

In addition, NR has a well-documented safety profile and is authorized as a Novel Food in the EU (Commission Implementing Regulation (EU) 2022/1160).

For those looking to explore NAD+ precursors with the strongest current scientific support, NR represents the option with the most robust evidence in humans. PLENIAGE® offers two formulations with NR chloride: PLENIAGE® Pro NAD+ NR Advanced, which incorporates 50 mg of NR chloride as part of a synergistic multi-ingredient formula (alongside Resveratrol, Quercetin, Berberine, Hyaluronic acid, Vitamin C and Piperine), and NR 300 mg, a single-ingredient product at the maximum dose authorized by the EU.

It should be clarified that the specific ingredient combination in Pro NAD+ NR Advanced has not been evaluated in its own clinical trials, and that the dose of NR chloride in each product (50 mg in Pro NAD+ NR Advanced; 300 mg in NR 300 mg) differs from the dose used in the Martens et al. (2018) study.

NADH vs NR: key differences when choosing an NAD+ precursor

If your goal is to maintain or raise NAD+ levels as part of a cellular vitality strategy, the comparison between NADH and NR is relevant. Both are routes to the same metabolic destination, but with very different evidence and bioavailability profiles.

NADH vs NR comparison table

When does NADH make sense?

The available research suggests that NADH could be relevant in very specific contexts: diagnosed chronic fatigue syndrome or situations of acute stress with sleep deprivation. In these contexts, the evidence, although preliminary, points to a possible effect on perceived fatigue.

When does NR make sense?

NR is the option with the strongest scientific support for those looking to maintain NAD+ levels in the context of healthy aging and cellular vitality. The evidence in humans is more robust, the bioavailability is higher and it has regulatory authorization in the EU.

To explore more about NAD+ precursors and cellular vitality, you can consult our complete cellular vitality guide and PLENIAGE®’s cellular vitality supplement collection.

Safety, side effects and contraindications of NADH

The safety profile of oral NADH at the doses studied (5–20 mg/day) appears favorable in the available studies, although the evidence base is limited.

Reported side effects

In the available clinical trials, oral NADH at doses of 10–20 mg/day was generally well tolerated. The most frequently reported adverse effects were mild and gastrointestinal: nausea, abdominal discomfort and transient loss of appetite. These effects were more frequent when taken with food.

Drug interactions

There are no solid data on drug interactions of oral NADH at supplemental doses. However, given its role in energy metabolism and the respiratory chain, caution is advised in people taking:

• Medications for neurological conditions (insufficient data)
• Anticoagulants (insufficient data)
• Chemotherapy (insufficient data)

Contraindications

No formal contraindications have been established for oral NADH at low doses in healthy adults. However, there are no safety data in:

• Pregnancy and breastfeeding
• Those under 18 years of age
• People with severe liver or kidney disease

Important notice: this information is for educational purposes and does not replace medical advice. Always consult your doctor or pharmacist before adding NADH or other supplements to your routine, especially if you have pre-existing health conditions or take medication.

NR at PLENIAGE®: the evolution toward next-generation NAD+ precursors

Research on NAD+ precursors has advanced significantly over the past decade. NADH was one of the first supplements in this space, but the accumulated evidence has pointed to NR (nicotinamide riboside) as the precursor with the greatest pharmacokinetic efficiency and clinical support in humans.

That scientific evolution is reflected in PLENIAGE®’s formulation. PLENIAGE® Pro NAD+ NR Advanced incorporates 50 mg of NR chloride as an NAD+ precursor in a synergistic formula that includes Resveratrol 147 mg (from Polygonum cuspidatum), Quercetin 71.25 mg (from Sophora japonica), Berberine 72.75 mg (from Berberis vulgaris), Hyaluronic acid 36 mg, Vitamin C 38.8 mg and Piperine 2.375 mg as a bioenhancer.

Each ingredient in this formula has been studied individually in the scientific literature. The specific combination of these ingredients in this formula has not been the subject of its own clinical trial with a control group.

For those looking for NR in a single-ingredient format, PLENIAGE® also offers NR 300 mg: pure NR chloride at the maximum dose authorized by the EU (300 mg/day, EU Reg. 2022/1160), with Fibregum (acacia fiber) as the sole natural excipient.

Both products are part of our cellular vitality collection, which brings together formulations with NR chloride—an NAD+ precursor authorized as a novel food in the EU (EU Reg. 2022/1160)—alongside other ingredients studied in the context of healthy aging.

NADH is a coenzyme with a central role in cellular energy metabolism. As a supplement, the available evidence suggests potential in specific contexts of chronic fatigue, with pilot studies showing reductions in perceived fatigue at 10 mg/day. The evidence base, however, is limited: the studies are small (n < 50), the designs have methodological limitations and there are no high-quality meta-analyses.

Research on NAD+ precursors has moved toward molecules with greater oral bioavailability and more robust evidence, such as NR (nicotinamide riboside). NR raises blood NAD+ levels in a documented way in human clinical trials and is authorized as a Novel Food in the EU.

If your interest is maintaining NAD+ levels in the context of healthy aging and cellular vitality, we invite you to explore PLENIAGE®’s cellular vitality collection, where you will find formulations based on NR chloride with the most up-to-date scientific and regulatory support.