Glutathione vs NAD+
Glutathione is the endogenous tripeptide gamma-glutamyl-cysteinyl-glycine, the principal intracellular thiol antioxidant and redox buffer. NAD+ is nicotinamide adenine dinucleotide, a pyridine dinucleotide that acts as a redox cofactor and as the obligatory substrate of the sirtuins, PARPs and CD38. They are set side by side because both are sold for broadly the same purpose, both are described as declining with age, and the two pools are chemically connected: NADPH is what regenerates oxidised glutathione. Direct evidence does exist, but not in the form the comparison implies. A series of randomised human trials of combined metabolic activators administered a glutathione precursor and an NAD+ precursor together, in a single formulation and a single arm, against placebo. No published study has compared glutathione with NAD+, or their precursors, as competing interventions, and no trial has administered either molecule itself in the form sold here.
They have been compared directly.
The studies that administered both did so simultaneously rather than competitively. The combined metabolic activator programme gives one fixed mixture of L-serine and N-acetyl-L-cysteine as glutathione precursors, nicotinamide riboside as an NAD+ precursor, and L-carnitine tartrate, and tests that mixture against placebo. Randomised, double-blinded, placebo-controlled phase 2 trials reported improved cognitive scores in Alzheimer's disease and, in Parkinson's disease, improved cognition with no improvement in motor function; a placebo-controlled study in non-alcoholic fatty liver disease reported reduced hepatic steatosis and lower transaminases; and phase 2 and phase 3 trials in mild-to-moderate COVID-19 reported shorter time to symptom-free recovery. Two acute human metabolomics studies varied one ingredient at a time inside the same mixture, comparing NAD+ precursors against each other in one and glutathione precursors against each other in the other, but never one class against the other. Animal work in rodent neurodegeneration models, in high-fat-fed hamsters and in diet-induced fatty liver mice follows the same co-administration design. Because the glutathione and NAD+ precursors always moved together, none of these studies can attribute a result to either. The remaining literature that engages both molecules does not administer them at all: a review of intravenous longevity infusion protocols lists both among the agents used and judges the evidence experimental; trials of NAD+ precursors alone measured glutathione as an outcome, with inconsistent results; and a large body of redox biology treats NAD(P)H and glutathione as coupled pools within one system, including work showing that a NAD(P)H-dependent enzyme suppresses ferroptosis independently of glutathione.
The 29 studies that tested both
- 01Human clinical2023
Combined metabolic activators improve cognitive functions in Alzheimer's disease patients: a randomised, double-blinded, placebo-controlled phase-II trial
Yulug B, et al. · Transl Neurodegener · randomised, double-blinded, placebo-controlled phase 2 trial in patients with Alzheimer's disease over 84 days, combined metabolic activators containing an NAD+ precursor together with glutathione precursors, with plasma metabolomics, proteomics and imaging (NCT04044131)
Alzheimer's Disease Assessment Scale-cognitive subscale scores improved significantly from baseline to day 84 in the treated group, and the decline in scores was significantly greater than placebo in patients with higher baseline scores. Hippocampal volume and cortical thickness measures supported the cognitive result, and plasma proteins and metabolites associated with NAD+ and glutathione metabolism improved after treatment. The NAD+ precursor and the glutathione precursors were given together in one formulation and were never set against each other.
- 02Human clinical2021
Combined Metabolic Activators Accelerates Recovery in Mild-to-Moderate COVID-19
Altay O, et al. · Adv Sci (Weinh) · placebo-controlled open-label phase 2 study and double-blinded phase 3 trial in ambulatory patients with mild-to-moderate COVID-19, combined metabolic activators comprising L-serine, N-acetyl-L-cysteine, nicotinamide riboside and L-carnitine tartrate
Time to complete symptom-free recovery was significantly shorter in the treated group than in placebo in both the phase 2 and the phase 3 trial. Plasma proteins and metabolites associated with inflammation and antioxidant metabolism improved relative to placebo. The trial addressed the deficiencies of NAD+ and glutathione metabolism described in COVID-19 by supplying precursors of both in a single mixture.
- 03Human clinical2025
Multi-omics characterization of improved cognitive functions in Parkinson's disease patients after the combined metabolic activator treatment: a randomized, double-blinded, placebo-controlled phase II trial
Yulug B, et al. · Brain Commun · randomised, double-blinded, placebo-controlled phase 2 trial in patients with Parkinson's disease over 84 days, combined metabolic activators comprising L-serine, N-acetyl-L-cysteine, nicotinamide riboside and L-carnitine tartrate, with UPDRS, Montreal Cognitive Assessment, functional MRI and plasma metabolomics and proteomics
No improvement in motor function was observed on the Unified Parkinson's Disease Rating Scale, the trial's main clinical endpoint. Cognitive function measured on the Montreal Cognitive Assessment improved significantly in the treated group over 84 days, with no such change in the placebo group. The glutathione precursors and the NAD+ precursor were components of one product administered in a single arm.
- 04Human clinical2021
Combined metabolic activators therapy ameliorates liver fat in nonalcoholic fatty liver disease patients
Zeybel M, et al. · Mol Syst Biol · placebo-controlled 10-week study in patients with non-alcoholic fatty liver disease, combined metabolic activators supplying NAD+ and glutathione precursors, integrated with plasma metabolomics, inflammatory proteomics and oral and gut metagenomics
Hepatic steatosis and levels of aspartate aminotransferase, alanine aminotransferase, uric acid and creatinine fell significantly in the treated group, while no differences on those variables were found in the placebo group after adjustment for weight loss. The precursors of the two molecules were administered as one product, so the design cannot attribute the effect to either.
- 05Human clinical2023
The acute effect of different NAD+ precursors included in the combined metabolic activators
Li X, et al. · Free Radic Biol Med · one-day double-blinded, placebo-controlled human study of six combined metabolic activator formulations differing only in their NAD+ precursor, with global plasma metabolomics
When the formulation contained no NAD+ precursor, the salvage pathway was the main source of the rise in NAD+. Nicotinamide produced the largest increase in NAD+ products, followed by niacin, nicotinamide riboside and nicotinamide mononucleotide, while flush-free niacin did not. Niacin produced a flushing reaction accompanied by decreased phospholipids and increased bilirubin derivatives. A glutathione precursor was present in every arm, so the comparison was between NAD+ precursors rather than between the two molecules.
- 06Human clinical2023
Longitudinal metabolomics analysis reveals the acute effect of cysteine and NAC included in the combined metabolic activators
Yang H, et al. · Free Radic Biol Med · placebo-controlled acute study in 70 healthy volunteers of combined metabolic activators containing either N-acetyl-L-cysteine or cysteine as the glutathione precursor, with or without nicotinamide or flush-free niacin, with longitudinal untargeted plasma metabolomics
The metabolic pathways affected were highly similar whether the glutathione precursor supplied was N-acetyl-L-cysteine or cysteine, provided nicotinamide was included. The cysteine-containing formulation was reported as well tolerated across the study. The design varied the glutathione precursor inside a mixture that also contained an NAD+ precursor, so again the two were co-administered rather than compared.
- 07Animal in vivo2024
Combined Metabolic Activators with Different NAD+ Precursors Improve Metabolic Functions in the Animal Models of Neurodegenerative Diseases
Altay O, et al. · Biomedicines · rat models of Alzheimer's and Parkinson's disease given two combined metabolic activator formulations (one with nicotinamide riboside, one with nicotinamide, each with L-serine, N-acetyl cysteine and L-carnitine tartrate) and their individual components, with brain and liver histology, immunohistochemistry, behavioural testing and apomorphine-induced rotation
Both formulations were associated with reduced hyperemia, degeneration and necrosis in neurons in the Alzheimer's and Parkinson's models and with reduced neuronal immunoreactivity; the nicotinamide-based formulation showed a greater effect than the nicotinamide riboside-based one. Metabolic improvements were also reported in liver tissue, and behavioural function improved in the Parkinson's model. Individual components were tested alongside the mixtures, but the reported outcomes were for the combinations.
- 08Animal in vivo2021
Combined Metabolic Activators Decrease Liver Steatosis by Activating Mitochondrial Metabolism in Hamsters Fed with a High-Fat Diet
Yang H, et al. · Biomedicines · hamsters fed a high-fat diet given chronic combined metabolic activator supplementation (nicotinamide riboside with the glutathione precursors betaine and N-acetyl-L-cysteine, plus L-carnitine tartrate) at two levels, with liver transcriptomics integrated into a liver-specific genome-scale metabolic model
Chronic supplementation significantly decreased hepatic steatosis in hamsters. Transcriptomic and metabolic-model analysis indicated activation of mitochondrial metabolism with modulation of global lipid, amino acid, antioxidant and folate metabolism. The paper also recounted an earlier one-day human proof-of-concept study in which the same class of mixture raised fatty acid oxidation and de novo glutathione synthesis.
- 09Animal in vivo2021
Supplementation with a Specific Combination of Metabolic Cofactors Ameliorates Non-Alcoholic Fatty Liver Disease, Hepatic Fibrosis, and Insulin Resistance in Mice
Quesada-Vazquez S, et al. · Nutrients · diet-induced non-alcoholic fatty liver disease model in male mice, four weeks of a combination of metabolic cofactors containing glutathione and NAD+ precursors (betaine, N-acetyl-cysteine, L-carnitine and nicotinamide riboside) after 16 weeks of high-fat, high-fructose/sucrose feeding
Treatment reduced liver steatosis, liver weight and hepatic lipid content and lowered serum transaminases. Hepatic fibrosis and Col1a1 expression decreased, expression of several proinflammatory cytokines fell, and Akt activation improved as a marker of insulin sensitivity. The glutathione and NAD+ precursors were supplied as a single cocktail.
- 10Review2026
Targeting mitochondrial metabolism with combined metabolic activators
Yang H, et al. · Trends Endocrinol Metab · review of the mechanistic rationale, preclinical evidence and clinical studies of combined metabolic activators and their individual components
The review summarised why glutathione and NAD+ precursors are combined in one formulation, collated the preclinical and early clinical evidence for that formulation and its components across several diseases, and assessed its translational potential and limitations. It reported no experiment setting glutathione against NAD+.
- 11Review2026
Intravenous longevity therapy: a critical review of evidence, mechanisms, and clinical utility
Godic A, Townsend J · Acta Dermatovenerol Alp Pannonica Adriat · critical review of intravenous high-dose vitamin, mineral, amino acid, coenzyme Q10, alpha-lipoic acid, glutathione and nicotinamide adenine dinucleotide protocols marketed as longevity therapy
Both compounds appear in the same review as agents infused for the same marketed purpose. The available data came mainly from preclinical models and small clinical series in disease-specific or aesthetic contexts, few studies used validated ageing biomarkers such as epigenetic age or telomere length, and placebo-controlled trials were scarce, underpowered or conflicting. The authors concluded that intravenous longevity therapy should be regarded as experimental rather than evidence-based.
- 12Human clinical2022
A Combination of Nicotinamide and D-Ribose (RiaGev) Is Safe and Effective to Increase NAD+ Metabolome in Healthy Middle-Aged Adults: A Randomized, Triple-Blind, Placebo-Controlled, Cross-Over Pilot Clinical Trial
Xue Y, et al. · Nutrients · randomised, triple-blind, placebo-controlled crossover pilot trial in healthy middle-aged adults, seven days of a nicotinamide and D-ribose combination
The blood NAD+ metabolome increased, with NADP+ rising significantly against both placebo and baseline, and increases in blood glutathione and high-energy phosphates were also observed. Overall blood glucose fell without a significant change in insulin secretion, waking salivary cortisol declined, and fatigue, concentration and motivation scores improved against baseline. Glutathione was an outcome measure here rather than an administered agent.
- 13Human clinical2020
Acute nicotinamide riboside supplementation improves redox homeostasis and exercise performance in old individuals: a double-blind cross-over study
Dolopikou CF, et al. · Eur J Nutr · double-blind crossover study in 12 young and 12 old men, acute nicotinamide riboside or placebo with blood and urine redox measures and physical performance testing
At rest the older men had lower erythrocyte NAD(P)H, lower erythrocyte glutathione and higher urinary F2-isoprostanes than the young. Nicotinamide riboside raised NADH and NADPH in both age groups and lowered F2-isoprostanes, while glutathione showed only a non-significant tendency to rise and only in the old. Isometric peak torque and the fatigue index improved in the old group alone, with no redox or physiological effect in the young.
- 14Animal in vivo2018
Nicotinamide riboside supplementation dysregulates redox and energy metabolism in rats: Implications for exercise performance
Kourtzidis IA, et al. · Exp Physiol · 38 Wistar rats in four groups (control, exercise, nicotinamide riboside, exercise plus nicotinamide riboside), 21 days of supplementation followed by an incremental swimming test to exhaustion
Nicotinamide riboside raised liver NADPH and plasma F2-isoprostanes and decreased erythrocyte glutathione peroxidase, glutathione reductase and catalase activity. Liver glycogen rose while plasma glucose fell. The authors concluded that supplementation disturbed energy and redox metabolism and impaired exercise performance in healthy rats.
- 15In vitro2025
NADH supplementation improves human oocyte maturation and developmental competence of resulting embryos in controlled ovarian hyperstimulation cycles: a pilot study implicating the CDK2/GAS6 signaling pathway
Zhang Q, et al. · Front Endocrinol (Lausanne) · discarded immature human oocytes from controlled ovarian hyperstimulation cycles randomised to in vitro maturation media supplemented with NADH across a concentration range, with mitochondrial phenotyping, single-cell RNA sequencing and intervention experiments
NADH in the culture medium raised maturation and blastocyst rates against untreated controls and increased ATP, mitochondrial membrane potential and glutathione while reducing reactive oxygen species. CDK2 and GAS6 were upregulated, and CDK2 inhibition suppressed maturation. Glutathione was recorded as a mitochondrial index rather than administered.
- 16Human clinical2025
NAD+ dyshomeostasis in RYR1-related myopathies
Lawal TA, et al. · Skelet Muscle · colorimetric redox assay of whole blood from 28 individuals with RYR1-related myopathy against a control dataset of 299, extended to human skeletal muscle, primary myotube cultures and Ryr1 Y524S mice, with nicotinamide riboside tested in vitro (NCT02362425)
Glutathione, NAD+ and NADP were measured together in the same participants. Most affected individuals showed systemic NAD+ deficiency and raised NADPH concentrations, and decreased NAD+/NADH and NADP/NADPH ratios were seen relative to controls. Nicotinamide riboside was applied to patient-derived myotube cultures, where it raised cellular NAD+ in a dose- and time-dependent manner, rather than being given to participants.
- 17Animal in vivo2022
Nicotinamide Mononucleotide Ameliorates Silica-Induced Lung Injury through the Nrf2-Regulated Glutathione Metabolism Pathway in Mice
Wang L, et al. · Nutrients · mouse silicosis model produced by intratracheal instillation of silica, nicotinamide mononucleotide treatment assessed at 7 and 28 days by histopathology, biochemistry and transcriptomics
Nicotinamide mononucleotide reduced lung damage and inflammatory infiltration, lowered reactive oxygen species and increased glutathione. Transcriptomic analysis indicated that immune response and glutathione metabolism were the main regulated pathways, with upregulation of Gstm1, Gstm2 and Mgst1 following nuclear translocation of Nrf2. Glutathione was an endogenous readout of the NAD+ precursor's effect rather than a co-treatment.
- 18In vitro2026
Reduced Versus Oxidized NAD+ Precursors Drive Distinct Transcriptomic, Proteomic, and Metabolic Profiles in Hepatocytes
Vinten KT, et al. · FASEB J · cultured murine hepatocytes treated with nicotinamide mononucleotide, reduced nicotinamide mononucleotide, nicotinamide riboside or reduced nicotinamide riboside, profiled by RNA sequencing, proteomics and metabolomics
The reduced precursors produced broader metabolic and transcriptional changes than the oxidised ones, and the genes shared between them included upregulated stress-related glutathione S-transferases, reflected again at protein level. That upregulation did not deplete glutathione or oxidised glutathione, which the authors read as a pseudo-stress response rather than genuine oxidative stress.
- 19Review2020
L-Glutamine in sickle cell disease
Cox SE, et al. · Drugs Today (Barc) · review of L-glutamine in sickle cell disease, covering red-cell redox biology and the randomised phase 2 and phase 3 trials
The review described L-glutamine as a conditionally essential amino acid required for synthesis of both nicotinamide adenine dinucleotide and glutathione, and reported that the NADH:[NAD+ + NADH] ratio in sickle red cells is lower than in normal red cells. Randomised trials showed L-glutamine to be safe and associated with fewer painful episodes and hospitalisations, while anaemia and haemolysis did not improve. Neither NAD+ nor glutathione was administered.
- 20Review2020
L-glutamine for sickle cell disease: Knight or pawn?
Sadaf A, Quinn CT · Exp Biol Med (Maywood) · review of the preclinical and clinical evidence for L-glutamine therapy in sickle cell disease
The review set out L-glutamine's role in the synthesis of reduced glutathione and of the cofactors NAD(H) and NADP(H), and stated that the relative impact of L-glutamine on the red-cell redox environment is not fully understood and that few therapeutic trials exist. Both molecules feature as downstream antioxidant-related products rather than as administered agents.
- 21Review2025
Redox regulation: mechanisms, biology and therapeutic targets in diseases
Li B, et al. · Signal Transduct Target Ther · broad review of redox signalling, its dysregulation and therapeutic targeting across disease
The review described NADPH and glutathione together as key molecules whose synthesis is raised by NRF2-mediated antioxidant responses, and framed disruption of that equilibrium as a route into disease. It reported that antioxidant-based therapies have shown early promise where oxidative stress is the primary pathology but that their efficacy in multifactorial disease remains controversial.
- 22Review2015· Russian (English abstract)
[Main Cellular Redox Couples]
Bilan DS, et al. · Bioorg Khim · review of the principal cellular redox couples and their measurement
The review treated NAD+/NADH, NADP+/NADPH and oxidised/reduced glutathione as the universal redox couples participating in the adjustment of many cellular reactions, and described the ratio of oxidised to reduced forms as an important cellular redox parameter. It is a description of shared redox chemistry rather than a study of either molecule as a treatment.
- 23Review2020
Metabolic Responses to Reductive Stress
Xiao W, Loscalzo J · Antioxid Redox Signal · review of reductive stress, redox compartmentalisation and cellular metabolism
The review defined reductive stress as excessive levels of NADH, NADPH and glutathione and argued that it is as harmful as oxidative stress and implicated in many pathological processes. It emphasised that the cellular pools of NAD(H), NADP(H) and glutathione are highly compartmentalised, so both molecules were treated as reducing equivalents within one homeostatic system.
- 24Review2020
Reductive stress in striated muscle cells
Bellezza I, et al. · Cell Mol Life Sci · review of reductive stress in cardiac and skeletal muscle
The review defined reductive stress as a sustained increase in the glutathione/glutathione disulfide and NADH/NAD+ ratios and documented its occurrence in several cardiomyopathies, in coronary artery disease and in myocardial infarction. Excess Nrf2 activation and hyperglycaemia-driven polyol-pathway flux were described as routes into that state.
- 25Review2014
The thioredoxin antioxidant system
Lu J, Holmgren A · Free Radic Biol Med · review of the thioredoxin system and its relationship to the glutathione-glutaredoxin system
The review described the thioredoxin system as composed of NADPH, thioredoxin reductase and thioredoxin, operating alongside the NADPH-dependent glutathione-glutaredoxin system to control the cellular redox environment. It reported that the mammalian thioredoxin and glutathione systems can supply electrons to each other and act as mutual backups, which is the biochemical basis for describing the two pools as linked rather than interchangeable.
- 26Animal in vivo2025
Elevating cytosolic NADPH metabolism in endothelial cells ameliorates vascular aging
Wu D, et al. · Nat Commun · genetically encoded fluorescent NADPH indicator in senescent endothelial cells with G6PD overexpression and knockdown, a screen of 1419 approved drugs, and angiotensin II-infused and naturally aged mice
Cytosolic but not mitochondrial NADPH rose during endothelial senescence, and G6PD overexpression alleviated while knockdown aggravated vascular ageing. The protective effect required NADPH and operated by increasing reduced glutathione and inhibiting HDAC3. Neither molecule was supplemented; the connection between them ran through the endogenous NADPH pool.
- 27Animal in vivo2025
G6PD deficiency triggers dopamine loss and the initiation of Parkinson's disease pathogenesis
Stykel MG, et al. · Cell Rep · murine and human pluripotent stem cell models of Parkinson's disease with human postmortem tissue
Accumulation of alpha-synuclein micro-aggregates impaired flux through the pentose phosphate pathway, lowering NADP(H) and glutathione levels and leading to dopamine oxidation and reduced total dopamine. Restoring either NADPH or glutathione by genetic and pharmacological means blocked dopamine oxidation and rescued steady-state dopamine, so the two were manipulated in parallel within one model rather than compared as treatments.
- 28In vitro2019
FSP1 is a glutathione-independent ferroptosis suppressor
Doll S, et al. · Nature · expression cloning screen in human cancer cells for genes able to complement loss of glutathione peroxidase 4
The screen identified ferroptosis suppressor protein 1, which suppresses ferroptosis independently of glutathione. The paper established that a NAD(P)H-dependent system operates in parallel to the glutathione-dependent GPX4 axis, which is the clearest published statement that the two redox pools are not simply substitutes for one another.
- 29In vitro2023
Phase separation of FSP1 promotes ferroptosis
Nakamura T, et al. · Nature · small-molecule library screen for inhibitors of ferroptosis suppressor protein 1 in cancer cell lines
The screen identified 3-phenylquinazolinones as FSP1 inhibitors acting by relocalising and condensing the protein rather than by competitive enzyme inhibition. The paper described FSP1 as using NAD(P)H as electron donor to prevent lipid peroxidation independently of the cysteine-glutathione-GPX4 axis, again treating the two systems as parallel rather than competing.
Side by side.
| Glutathione | NAD+ | |
|---|---|---|
| Evidence maturity | Early clinical | Early clinical |
| Studies cited here | 15 | 15 |
| Published 2023 or later | 9 | 11 |
| Newest paper | 2026 | 2026 |
| Molecular class and origin | An endogenous tripeptide, gamma-L-glutamyl-L-cysteinyl-glycine, synthesised inside cells in two ATP-dependent steps and present at millimolar concentrations. Its gamma-linkage resists ordinary peptidases and its cysteine thiol carries out its chemistry. | An endogenous pyridine dinucleotide rather than a peptide, built from nicotinamide and adenine nucleotides. It is consumed as a substrate by sirtuins, PARPs and CD38 as well as cycled as a redox carrier, so reviews describe its concentration as a dynamic set point. |
| Mechanism as described in the literature | Electron donation from the reduced form, oxidation to the disulfide GSSG, and recycling by glutathione reductase using NADPH. It also serves as cosubstrate for glutathione peroxidase and for the glutathione S-transferases in conjugation reactions. | Hydride transfer in glycolysis, the tricarboxylic acid cycle and oxidative phosphorylation, plus cleavage by NAD+-consuming enzymes. The ageing rationale rests on reported declines in tissue NAD+ and on competition between sirtuins, PARPs and CD38 for one pool. |
| Route and systemic availability | Oral bioavailability is contested and strongly formulation-dependent; randomised crossover pharmacokinetic studies report substantially different systemic exposure between standard, micellar, liposomal and orally dissolving film preparations of the same compound. | Poorly absorbed orally, so almost all human work has used the precursors nicotinamide riboside and nicotinamide mononucleotide rather than NAD+ itself. Randomised trials consistently report that these raise circulating NAD+ two- to threefold. |
| Size and character of the evidence base | Small trials across three separate strands: pharmacokinetics of oral formulations, dermatological trials for skin pigmentation, and precursor-based repletion. A 2025 systematic review of skin lightening identified five randomised trials of oral glutathione and only one placebo-controlled study of the intravenous route. | A larger and more consistent randomised literature, but almost entirely of precursors. A 2026 systematic review and meta-analysis pooled 15 parallel randomised controlled trials of oral nicotinamide mononucleotide, and a 2025 meta-analysis covered both precursors for skeletal-muscle outcomes. |
| Best-characterised human finding | Repeated oral dosing raises body stores. A 6-month randomised placebo-controlled trial in 54 adults reported increases in erythrocyte, plasma, lymphocyte and buccal-cell glutathione that returned to baseline after a washout month. | Precursors reliably raise circulating NAD+. Trials report two- to threefold increases sustained over weeks to months, with tolerability across a wide range of intakes and no consistent laboratory safety signal. |
| Where controlled human trials have been negative | Neurodegeneration. A double-blind placebo-controlled phase 2b trial of intranasal glutathione in Parkinson's disease found no superiority over placebo, and a 2026 systematic review judged the evidence for glutathione itself inconclusive while finding more signal for N-acetylcysteine. | Function and metabolism. Meta-analyses found no effect of the precursors on muscle mass, grip strength, gait speed, body weight, fasting glucose, HbA1c, lipids or systolic blood pressure, and a 24-week long-COVID trial found no cognitive, fatigue or sleep benefit despite sustained NAD+ elevation. |
| Safety signals reported | Reviews of the intravenous route describe anaphylaxis and hepatotoxicity, and one participant in the intranasal Parkinson's trial developed cardiomyopathy. Oral use over weeks to months has not produced consistent changes in liver enzymes or creatinine in the published trials. | A 2026 meta-analysis found no increase in overall, serious or system-specific adverse events and no rise in ALT or AST with oral nicotinamide mononucleotide. Higher dropout in the treated arm was reported in one long-COVID trial, and niacin-containing formulations produced flushing. |
| Regulatory status and basis of most marketing claims | Not an approved treatment for skin lightening, anti-ageing or general wellness in any major jurisdiction. Claims generally extrapolate from redox biology and from precursor trials such as glycine plus N-acetylcysteine rather than from trials of glutathione administered as sold. | Not an approved medicine for any longevity indication. Claims generally extrapolate from rodent lifespan and stem-cell work and from the reliable rise in blood NAD+, neither of which the human functional endpoints have confirmed. A 2026 review classifies intravenous use of both as experimental. |
And what it does not.
The two have been given together and never against each other. Every study that administered both supplied a glutathione precursor and an NAD+ precursor inside one fixed mixture with two further ingredients, so its results describe the mixture and cannot be attributed to either molecule, let alone used to rank them. Read separately, the evidence bases are asymmetric rather than opposed. NAD+ precursors have the larger and more consistent randomised literature and a reliably reproduced biochemical effect, but meta-analyses of muscle, metabolic and cognitive endpoints have been null, and the compound sold is not the one those trials used. Glutathione has smaller trials spread across pharmacokinetics, dermatology and precursor repletion, a demonstrated ability to raise body stores that reverses on withdrawal, and a controlled neurodegeneration trial that failed. The chemistry links them, since NADPH is what regenerates oxidised glutathione, but the ferroptosis work shows that the two systems can also operate independently of each other. Nothing published supports a preference for one over the other.
Common questions.
- Have glutathione and NAD+ been administered to the same participants in a single published trial?
Their precursors have. The combined metabolic activator trials gave N-acetyl-L-cysteine and L-serine as glutathione precursors alongside nicotinamide riboside as an NAD+ precursor, in one fixed mixture with L-carnitine tartrate, in a single treatment arm compared against placebo. Neither glutathione nor NAD+ itself was administered, and the two classes of precursor were never separated into different arms. No published trial has given the two molecules to the same participants as distinct comparators.
- What did the combined metabolic activator trials actually test?
They tested one four-ingredient mixture against placebo across several conditions. Randomised, double-blinded phase 2 trials reported improved cognitive scores in Alzheimer's disease and improved cognition without motor improvement in Parkinson's disease. A placebo-controlled study in non-alcoholic fatty liver disease reported reduced hepatic steatosis and lower transaminases, and phase 2 and phase 3 trials in mild-to-moderate COVID-19 reported shorter time to symptom-free recovery. Because the ingredients moved together, none of these results isolates the contribution of the glutathione or the NAD+ component.
- Does raising the NAD+ pool change glutathione levels, or the reverse?
Studies that raised NAD+ have measured glutathione, with inconsistent results. A crossover trial of a nicotinamide and D-ribose combination reported increased blood glutathione alongside the NAD+ metabolome. An acute nicotinamide riboside crossover study found only a non-significant tendency for erythrocyte glutathione to rise, and only in older participants. A 21-day rat study found reduced erythrocyte glutathione peroxidase and glutathione reductase activity. In cultured hepatocytes, reduced NAD+ precursors upregulated glutathione S-transferases without depleting glutathione.
- What has been published on intravenous administration of either compound?
A 2026 critical review examined infusion protocols marketed as longevity therapy and listed both glutathione and nicotinamide adenine dinucleotide among the agents given. It reported that the data came mainly from preclinical models and small clinical series in disease-specific or aesthetic settings, that few studies used validated ageing biomarkers, and that placebo-controlled trials were scarce, underpowered or conflicting. Dermatology reviews separately describe anaphylaxis and hepatotoxicity with intravenous glutathione. Both were judged experimental rather than evidence-based.
- Is the energy-versus-antioxidant framing supported by the literature?
Only as a simplification. Reviews of cellular redox couples treat NAD+/NADH, NADP+/NADPH and oxidised/reduced glutathione as three universal couples within one system, and the thioredoxin literature reports that the glutathione and NADPH-dependent systems can supply electrons to each other. Glutathione is not only an antioxidant, since it is also the cosubstrate for conjugation reactions, and NAD+ is not only an energy carrier, since it is consumed as an enzyme substrate. Work on ferroptosis identified a NAD(P)H-dependent pathway operating independently of glutathione.
For research purposes only. Not for human consumption, diagnosis, treatment, or prevention of any condition. Nothing on this page is medical advice, and no comparison here should be read as a recommendation of either compound.