Comparison
NAC (N-acetylcysteine) vs. Glutathione
NAC or glutathione – what actually reaches the body?
The short answer
The difference is a digestion problem. Oral glutathione meets the degrading enzyme gamma-glutamyl transferase in the gut; after a single dose, it did not rise in the plasma of healthy people, and two randomized trials over six months and four weeks reached opposite results – the basic assumption of the marketing, that swallowing it raises the glutathione level in the cell, has not been convincingly shown in humans. NAC instead supplies cysteine, the rate-limiting building block from which the body makes glutathione itself. In addition, NAC is approved as a medicine, is used as an antidote in paracetamol poisoning and has meta-analytic evidence in COPD. That NAC broadly raises the glutathione level in healthy people has not been shown either, however; it is supported mainly in its approved indications.
The numbers side by side
| Axis | NAC (N-acetylcysteine) | Glutathione | Difference |
|---|---|---|---|
| Human evidenceHow much and how good the data in humans are | 8 | 5 | NAC better studied |
| MechanismHow well the chain of action is understood | 8 | 5 | NAC better studied |
| Safety dataHow well safety has been studied – not how safe it is | 9 | 6 | NAC better studied |
| Hype gap10 means: the advertising stays level with the data | 4 | 3 | NAC closer to the data |
| Track record of useHow much documented use in humans exists – does not measure whether it works | 10 | 7 | NAC in use longer |
| Rating | Well supported, heavily overhyped · Thin human evidence | ||
“Track record of use” measures how long and how widely something has been used in humans – not whether it works. The BK-Score is a subjective assessment by Biohacking Kompakt based on published scoring rules (German). It is not a scientific rating, not the consensus of a professional society and not a medical recommendation.
Why these numbers
NAC (N-acetylcysteine)
Two worlds in one entry, and the dividing line runs along the legal status. In Germany, NAC is not a food supplement but an approved medicine: orally as a mucolytic, pharmacy-only and available without prescription; as an antidote, prescription-only. The approved indication is the yardstick, and it is unusually well measured: in the analysis of the US national multicenter program (Smilkstein et al., N Engl J Med 1988, PMID 3059186), of 2,540 orally treated patients, 6.1% of the at-risk patients developed liver damage when treatment started within 10 hours, 26.4% when it started after 10 to 24 hours and 41% of high-risk patients after 16 to 24 hours; 11 patients died. This is a chain of action quantified in humans, hence mechanism 8 instead of 7 - but only for this indication. In COPD, there is a meta-analysis of 14 RCTs with 2,856 patients (Cai et al., PeerJ 2026, PMID 42473447): RR 0.87 (95% CI 0.79 to 0.96) for acute exacerbations, without improvement in FEV1, FVC, quality of life and glutathione levels. PANTHEON (Zheng et al., Lancet Respir Med 2014, PMID 24621680) reached the primary endpoint with 1,006 patients (1.16 versus 1.49 exacerbations per patient-year, RR 0.78), BRONCUS (Decramer et al., Lancet 2005, PMID 15866309) missed both primary endpoints with 523 patients over three years, and a trial in 968 patients with mild to moderate COPD (Zhou et al., Nat Commun 2024, PMID 39349461) missed both co-primary endpoints. The German National Disease Management Guideline (Nationale VersorgungsLeitlinie) COPD therefore gives only an open recommendation (recommendation 5-8) and states that there is no evidence for use in the acute situation. The psychiatry figure in the existing entry is correct (Peng et al., Gen Hosp Psychiatry 2024, PMID 39504621: 12 RCTs, 904 patients, SMD −0.24), but remains small; in obsessive-compulsive disorder, the meta-analysis rests on 6 RCTs with 195 patients and reaches p = 0.05 only in the window of five to eight weeks (PMID 39376972), and for craving in addiction, the largest trial, with 302 adults, was negative (PMID 28623823). Evidence at 8: approval for a clearly defined indication plus consistent meta-analytic data in COPD, but only small and inconsistent data for the advertised biohacking applications. Use at 10, because the substance has been used for decades under approval in emergency medicine and without prescription in self-medication. Hype stays at 4: the advertised core, the broad raising of glutathione levels in healthy people, has not been shown in humans - 6,000 mg daily over 28 days did not significantly raise brain glutathione in an open-label study in 8 people, 5 of them with Parkinson’s disease (Coles et al., J Clin Pharmacol 2018, PMID 28940353), and the COPD meta-analysis found no change in glutathione levels. Oral bioavailability is 4.0 to 9.1% (Olsson et al., Eur J Clin Pharmacol 1988, PMID 3360052). Liver protection against alcohol is not supported: in severe alcoholic hepatitis, prednisolone plus NAC missed six-month mortality in 174 patients (27% versus 38%, p = 0.07; PMID 22070475); in acute liver failure unrelated to paracetamol, intravenous NAC missed overall survival in 173 patients (70% versus 66%), but improved transplant-free survival (40% versus 27%), especially in early stages - a hospital treatment and not evidence of liver protection in everyday life (PMID 19524577). In fertility, Cochrane rates the live birth rate as very low certainty, and after excluding the studies at high risk of bias, nothing significant remains (PMID 35506389). In pulmonary fibrosis, the data are clearly negative (PMID 24836309). Hence mixed rather than positive.
Glutathione
The weak point lies before the effect: oral glutathione meets gamma-glutamyl transferase in the gut, and after a single dose, neither glutathione nor cysteine nor glutamate rose in the plasma of seven healthy people over 270 minutes. Against this stands the longest study: six months, 54 adults, randomized and double-blind, with 30 to 35 percent higher stores in erythrocytes, plasma and lymphocytes and 260 percent in buccal mucosal cells – reported relative to baseline. A four-week randomized trial in 40 adults, by contrast, found no change in oxidation markers or in glutathione itself. The contradiction has not been resolved, and all endpoints are surrogate values. The most consistent finding is the smallest: a slight decrease in the melanin index on sun-exposed skin. For detoxification, immune strengthening and anti-aging, robust human data are lacking; long-term data beyond six months do not exist. Intravenous use for skin lightening has drawn objections from the authorities.
Frequently asked questions
Does oral glutathione not work at all?
For skin lightening, there are small studies with positive results whose methodological quality is consistently rated as low. For detoxification, immune strengthening and anti-aging, no robust human evidence was found. Whether the oral form raises the level at all is open: a six-month study with 54 adults found higher stores, a four-week study with 40 adults found no change. Infusions are a different product with their own risks; intravenous use for skin lightening has drawn objections from the authorities.
Does that make NAC an anti-aging agent?
No. The solid evidence comes from medical indications – antidote and COPD. For depression, there is a meta-analysis of twelve RCTs with 904 patients, whose effect is small. For healthy adults seeking rejuvenation, this data base does not exist.
What is GlyNAC?
The combination of glycine and NAC, i.e. both glutathione precursors together. The claim that it reverses features of aging goes back to a study with 24 older adults from a single research group, without independent replication.
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Information only, not medical advice and not a usage or dosage recommendation. Prescription-only and unapproved substances belong in a doctor's hands.