Short answer: NAC is an FDA-approved drug for acetaminophen overdose and a building block the body uses to make glutathione.1 Only about 4% to 9% of oral NAC reaches the blood.2 A single 3 g dose of oral glutathione did not raise blood levels,3 but 1,000 mg a day for 6 months raised body stores 30% to 35%.4 We found no trial comparing them.
| NAC (N-acetylcysteine) | Glutathione | |
|---|---|---|
| What it is | A form of cysteine; approved as Acetadote for acetaminophen overdose1 | A three-amino-acid molecule the body makes3 |
| Supplement status | Excluded from the supplement definition; FDA uses enforcement discretion since 20225 | Sold as a dietary supplement6 |
| Oral absorption | 4.0% (reduced) to 9.1% (total) of a 400 mg dose2 | About 3 g once: no significant rise in blood3 |
| Longer use | Not covered in the sources checked | 1,000 mg a day for 6 months: stores up 30% to 35%, back to baseline a month after stopping4 |
| Half-life | Total NAC about 6.25 hours after an oral dose2 | Not established for oral use in the sources checked |
NAC was approved as a drug before it was sold as a supplement, so FDA considers it excluded from the legal definition of a dietary supplement. In an August 2022 final guidance, FDA said it intends to use enforcement discretion for NAC products labeled as supplements that otherwise follow the law.5
In 6 volunteers, 4.0% of an oral NAC dose reached the blood as reduced NAC and 9.1% as total NAC.2 For glutathione, a single dose of about 3 g in 7 volunteers did not significantly raise blood glutathione, cysteine or glutamate, because the gut and liver break it down.3 In a 6-month trial of 54 adults, though, 1,000 mg a day raised glutathione 30% to 35% in red cells, plasma and white cells; levels returned to baseline after a month off.4
No study we found gave people NAC and glutathione side by side. These are study protocols, not personalized advice; confirm any dosing with your prescriber. More detail: the NAC (N-Acetylcysteine) and Glutathione guides.