One is a finished molecule; the other is a building block the body uses to make it. Glutathione is a three-amino-acid peptide that cells make for themselves. NAC — N-acetylcysteine, or acetylcysteine on a drug label — supplies cysteine, the scarcest of those three ingredients. Readers weigh the two against each other because both are sold as ways to raise glutathione. On the record, they are not equals: one is an approved drug with a defined use, the other has no approved product at all.
What glutathione injections are claimed to do, and what the trials found, is on our glutathione injection benefits page; the comparison of injected and oral glutathione on our glutathione injection vs oral page; harms on our glutathione injection side effects page. Skin lightening is outside this page and covered by PeptideGlowJournal's glutathione for skin page. Nothing here is a recommendation.
Side by side
| Glutathione | NAC (acetylcysteine) | |
|---|---|---|
| What it is | Tripeptide: glutamate, cysteine, glycine | One modified amino acid |
| Approved drug | None (oxidised glutathione is one ingredient of an eye-surgery irrigation fluid) | Yes: IV antidote (Acetadote, generics); 10%/20% solution, inhaled or oral |
| Approved use | — | Acetaminophen overdose; thick mucus in lung disease |
| How it reaches people | Compounded injections and IV drips; oral supplements | Prescription drug; also sold as a supplement under FDA enforcement discretion |
| Relationship to glutathione | Is glutathione | Supplies cysteine, the usual limit on making it |
| Best human evidence | Small trials of oral supplements; small injected-use trials | Decades of overdose use; labelled efficacy |
NAC's approved record
The Acetadote label (Cumberland Pharmaceuticals, DailyMed, effective 30 April 2025, read 22 October 2026) approves intravenous acetylcysteine "to prevent or lessen hepatic injury after ingestion of a potentially hepatotoxic quantity of acetaminophen" in adults and children weighing 5 kg or more. After a single intravenous dose its mean terminal half-life is 5.6 hours. Its most common adverse reactions (over 2%) are rash, urticaria or facial flushing and itching, and its first warning is hypersensitivity.
The acetylcysteine solution label (Hospira, DailyMed, effective 22 May 2026, read 22 October 2026) covers two older uses of the same 10% and 20% solution: inhaled, as adjuvant therapy for "abnormal, viscid, or inspissated mucous secretions" in chronic and acute lung disease and cystic fibrosis; and by mouth, diluted, as the same overdose antidote, started "as soon as possible after the overdose and, in any case, within 24 hours". Inhaled, its listed adverse effects include stomatitis, nausea and bronchoconstriction.
Both labels give the same mechanism for the liver: at overdose the normal routes for clearing acetaminophen saturate, a toxic metabolite builds up and uses up the liver's glutathione, and acetylcysteine "probably protects the liver by maintaining or restoring the glutathione levels, or by acting as an alternate substrate" for that metabolite. Benefit is seen "principally in patients treated within 16 hours." That is the strongest human evidence that raising the body's capacity to make glutathione does something measurable — in a poisoning, with a dose by body weight, in hospital.
Glutathione's record
Glutathione has no approved drug. Drugs@FDA (openFDA, data of 20 October 2026) lists two applications containing it, both the same eye-surgery irrigation formula in which oxidised glutathione is one of eight ingredients (Alcon's BSS Plus, still marketed); DailyMed's 57 glutathione listings are supplements and unapproved homeopathic products. The injections sold by clinics are compounded, and their record is set out on our benefits page. As an oral supplement, the two placebo-controlled trials usually cited disagree:
| Trial | People | Dose | Length | Glutathione result |
|---|---|---|---|---|
| Allen & Bradley 2011 | 40 healthy adults | 500 mg twice daily | 4 weeks | No change in red-cell glutathione or oxidative-stress markers |
| Richie 2015 | 54 non-smoking adults | 250 or 1,000 mg daily | 6 months | Up 30–35% in red cells, plasma and lymphocytes at 1,000 mg; back to baseline after a 1-month washout |
The difference may be duration — the Richie trial saw rises after one month but measured over six — or dose and measurement method; neither trial was designed to settle which. Neither measured a health outcome.
The one head-to-head trial
A PubMed search for randomised trials in people comparing NAC with glutathione returned one record on 22 October 2026: Schmitt 2015, Redox Biology. Twenty volunteers with metabolic syndrome took NAC, oral glutathione and a new sublingual glutathione, three weeks each, in random order. The authors report that the sublingual form raised plasma glutathione and the reduced-to-oxidised ratio more than oral glutathione, and conclude it was superior to both oral glutathione and NAC "in terms of GSH supplementation."
Three limits apply. It is small and short. The outcome is a blood marker, not a health effect. And two of its four authors list Laboratoires Le Stum, the company developing the sublingual form, as their affiliation. It does not show that either NAC or oral glutathione fails; it shows one manufacturer's product did better on its chosen markers.
The building-block argument, tested
The case for NAC over glutathione is biochemical: swallowed glutathione is largely broken down in the gut, while cysteine is what limits how fast cells assemble it. The best-known human test of that idea used NAC with glycine, another of glutathione's three parts. In the GlyNAC trial (Kumar 2023), 24 older adults were randomised to GlyNAC or an alanine placebo for 16 weeks (12 per group), with 12 young adults as a reference group. The authors report that GlyNAC, and not placebo, improved glutathione deficiency, oxidative stress, mitochondrial function, insulin resistance, gait speed and strength. It is one small trial from one group, and it tested a combination — it is not evidence for NAC alone, and it does not compare NAC with glutathione.
The regulatory oddity
NAC sits in an unusual place. Because it was approved as a drug before it was marketed as a supplement, the law excludes it from the definition of a dietary supplement. FDA's final guidance of August 2022 says the agency intends to exercise enforcement discretion over NAC products labelled as supplements that would otherwise be lawful (Federal Register, 2 August 2022). So the same molecule is a prescription antidote in hospital and a capsule on a pharmacy shelf. Glutathione supplements carry no such history; injectable glutathione's position under compounding rules is on our can doctors prescribe peptides page.
What is not established
- Which raises glutathione more in healthy people. One 20-person, three-week, manufacturer-linked crossover trial is the whole head-to-head record.
- Whether raising blood glutathione improves any health outcome outside acetaminophen poisoning, where NAC's benefit rests on liver protection.
- NAC alone on the outcomes GlyNAC reported; those results are for the combination.
- Injected glutathione against NAC: no trial located compared them.
Anyone weighing NAC for a medical reason is weighing a drug with labelled warnings; that conversation belongs with a physician or pharmacist.
Sources and dates
- Acetadote (acetylcysteine) injection label, Cumberland Pharmaceuticals, DailyMed set 472f158a-5ab9-4308-8e49-1116e6ea3d39, effective 30 April 2025 — read 22 October 2026.
- Acetylcysteine solution label, Hospira, DailyMed set 5558a5f5-e821-473b-7d8a-5d33d09f0586, effective 22 May 2026 — read 22 October 2026.
- Allen J, Bradley RD. J Altern Complement Med 2011;17(9):827–33 (PMID 21875351); Richie JP Jr et al. Eur J Nutr 2015;54(2):251–63 (PMID 24791752); Schmitt B et al. Redox Biol 2015;6:198–205 (PMID 26262996); Kumar P et al. J Gerontol A Biol Sci Med Sci 2023;78(1):75–89 (PMID 35975308) — abstracts read 22 October 2026.
- Drugs@FDA via openFDA,
products.active_ingredients.name:glutathione(2 applications: NDA018469 BSS Plus, NDA020079) and DailyMed search "glutathione" (57 listings) — 22 October 2026. - PubMed search for randomised human trials comparing acetylcysteine and glutathione (1 result) — run 22 October 2026.
- FDA, "Policy Regarding N-acetyl-L-cysteine; Guidance for Industry; Availability", Federal Register 2022-16499, 2 August 2022 — abstract read 22 October 2026.