Human research on NAD infusions comes from two studies: in a pilot study plasma NAD levels began to change only after the first two hours of a six-hour infusion, and a 2026 study found no meaningful changes in liver enzymes, inflammatory markers, kidney parameters or thyroid function. For glutathione the question is not the molecule, which is uncontroversial, but giving it by injection.
NAD and glutathione end up in the same category not because they work alike, but because people buy them for the same reason: energy, recovery and slowing down what age does to the body. Both molecules occur naturally in you and both decline over the years. That is where the similarity ends, and the differences that begin there are worth knowing before you buy.
What are NAD and glutathione?
NAD, nicotinamide adenine dinucleotide, is a coenzyme and not a peptide. It takes part in oxidation and reduction reactions and in energy metabolism: in glycolysis, the citric acid cycle and oxidative phosphorylation. It is also involved in DNA repair and in the formation of new mitochondria. It is sold alongside peptides, but it does not belong to that group.
Glutathione is a tripeptide built from cysteine, glycine and glutamic acid. Every cell in the body makes it, it acts as an antioxidant and it takes part in detoxification. Its concentration also falls with age. These facts concern the molecules themselves and are not disputed.
Why is NAD given intravenously?
The reason is absorption. Oral forms have poor bioavailability because they are broken down in the digestive tract, which is why the literature describes intravenous infusion as the established way of raising NAD levels in the body. That point carries a second one with it, and it needs saying plainly: the research sellers cite concerns drips run under supervision, not injections given at home.
What has research in humans shown about NAD?
A pilot study using a six-hour intravenous infusion produced a result that rarely reaches product copy. For the first two hours of the infusion no change was seen in plasma levels of NAD or its metabolites. Changes appeared only later, which means the molecule does not act the moment the drip is connected.
A second study, published in 2026 in Frontiers in Aging, compared NAD infusions with nicotinamide riboside infusions under ordinary practice conditions. Participants receiving NAD reported moderate and severe gastrointestinal complaints, a faster heart rate and chest tightness. The nicotinamide riboside group had milder symptoms: tingling and minor cramps. NAD infusions took 97 minutes on average, nicotinamide riboside infusions 37 minutes.
The same study also brought good news. No meaningful changes were found in liver enzymes, inflammatory markers, kidney parameters or thyroid function. The symptoms were unpleasant, then, but they did not show up in laboratory results.
Injected glutathione: what is known
With glutathione the argument runs along a different line than with NAD. The questions concern not the molecule itself but giving it by injection for cosmetic purposes, where data are scarce.
A case reported in 2019, with adverse effects after a compounded L-glutathione preparation, was linked to a probable high endotoxin level, that is, to the purity of the preparation. That is why the batch certificate matters with glutathione.
A 2025 systematic review found only one placebo-controlled study of intravenous glutathione for skin lightening. Improvement was seen in 6 of 16 people against 3 in the placebo group, and the difference was not statistically significant. There are no guidelines on dose or duration of use either. Reviews of the literature list the risk of toxic effects on the liver, kidneys and nervous system, anaphylaxis, and Stevens-Johnson syndrome.
How does an intravenous infusion differ from a subcutaneous injection?
This is the question that decides how much all the data above is worth to a buyer. An intravenous infusion is given over many minutes or hours, in a clinic, watched by staff who can stop it. A subcutaneous injection of a lyophilisate dissolved at home is a different route, a different absorption rate and no supervision.
Results from one route are not carried across to the other. That is why neither of these products in this shop comes with a dosing protocol: there is no research from which one could be derived for subcutaneous injection, and choosing a dose is a doctor's job.
| Feature | NAD | Glutathione |
|---|---|---|
| Type of molecule | Coenzyme | Tripeptide |
| Research in humans | Intravenous infusions, including a comparative study from 2026 | One placebo-controlled study of infusions for skin lightening, with no significant difference |
| Reported adverse effects | Stomach complaints, faster heart rate, chest tightness | Nausea, vomiting, chills, risk of severe reactions |
What is available in the shop?
Two items from this group are stocked: NAD and glutathione. Both come as a lyophilisate that has to be dissolved before use, and both are sold as research material.
Preparing the solution is described step by step in the article on reconstitution with bacteriostatic water, and storage conditions in the guide to keeping lyophilised powder and made-up solution. If you want to know what may be bought at all and in what capacity, that is set out in the article on the legal status of peptides. The wider picture of molecules acting on metabolism and muscle is in the article on the IGF-1 axis, MGF and myostatin.
Frequently asked questions
Is NAD a peptide?
No. NAD is a coenzyme involved in energy metabolism and DNA repair. It is sold alongside peptides but belongs to a different group of compounds.
Why is NAD given intravenously rather than orally?
Oral forms have poor bioavailability because they are broken down in the digestive tract. That is why research in humans concerns intravenous infusions.
How quickly does an NAD infusion act?
In a pilot study using a six-hour infusion, no change in plasma NAD or its metabolites was observed during the first two hours.
Does injected glutathione lighten skin?
The only placebo-controlled study of intravenous glutathione showed no significant difference.
What adverse effects were reported after NAD infusions?
Moderate and severe stomach complaints, a faster heart rate and chest tightness. No changes were found in liver enzymes or kidney parameters.
Where this information comes from
The description of NAD as a coenzyme of energy metabolism and DNA repair, and of glutathione as a tripeptide of cysteine, glycine and glutamic acid, comes from biochemistry reference material. The pilot study with a six-hour infusion and the absence of change during the first two hours, and the 2026 comparison of NAD with nicotinamide riboside infusions published in Frontiers in Aging, come from those publications. The case of seven patients given 1400 mg of L-glutathione comes from a United States FDA communication of February 2019. These sources were checked on 6 September 2026.
This is information about products and about the state of the research, not medical advice. NAD and glutathione are sold as research materials; judging whether any use is warranted, and choosing a dose, is a doctor's job.
Sources
- Grant R, Berg J, Mestayer R et al. A Pilot Study Investigating Changes in the Human Plasma and Urine NAD+ Metabolome During a 6 Hour Intravenous Infusion of NAD. Frontiers in Aging Neuroscience, 2019, 11: 257. https://doi.org/10.3389/fnagi.2019.00257
- Reyna K, Heinzen G, Patel N et al. Intravenous infusion of nicotinamide adenine dinucleotide (NAD+) versus nicotinamide riboside (NR): a retrospective tolerability pilot study in a real-world setting. Frontiers in Aging, 2026, 7: 1652582. https://doi.org/10.3389/fragi.2026.1652582
- FDA highlights concerns with using dietary ingredient glutathione to compound sterile injectables. US Food and Drug Administration (FDA), 2019. https://www.fda.gov/drugs/human-drug-compounding/fda-highlights-concerns-using-dietary-ingredient-glutathione-compound-sterile-injectables
- Sarkar R, Yadav V, Yadav T et al. Glutathione as a skin-lightening agent and in melasma: a systematic review. International Journal of Dermatology, 2025, 64(6): 992-1004. https://doi.org/10.1111/ijd.17535