NAC

N-Acetyl Cysteine

Evidence & Status

  • FDA Approved
  • Strong Human Evidence
  • Established

At a Glance

N-Acetyl Cysteine — a well-established acetylated form of the amino acid cysteine, used for over 50 years as a mucolytic and as the definitive treatment for acetaminophen overdose. Extensively studied as a glutathione precursor, antioxidant, and anti-inflammatory agent across a wide range of conditions.

Plain English

Researchers study NAC because it is the most efficient way to raise glutathione levels in the body — the cell's primary antioxidant defense system. Scientists are interested in its wide-ranging effects across different medical contexts: it is the standard treatment for acetaminophen overdose (where it prevents liver damage by restoring depleted glutathione), and has been studied in respiratory conditions, psychiatric disorders, liver disease, fertility, and more. With decades of human safety data and a well-understood mechanism, NAC is one of the most thoroughly characterized compounds in this database.

Overview

A cysteine prodrug and direct precursor to intracellular glutathione (GSH), the body's primary endogenous antioxidant. FDA-approved as an antidote for acetaminophen overdose (via IV route) and as a mucolytic for COPD and cystic fibrosis. Widely used off-label for liver protection, OCD, PTSD, addiction, and as a general antioxidant adjunct. Extensive clinical evidence base.

Research Summary

NAC has one of the broadest and deepest human evidence bases in this database. Efficacy for acetaminophen overdose is definitively established — FDA-approved IV formulation (Acetadote, NDA 018829) is the standard of care for acetaminophen toxicity. Mucolytic efficacy for COPD and cystic fibrosis is supported by multiple RCTs and international guidelines. Psychiatric applications including OCD have positive RCT evidence (Afshar et al., 2012, add-on RCT in refractory OCD), though the broader controlled evidence base in psychiatry is mixed and effect sizes are modest; NAC efficacy for OCD should not be characterized as settled. The COVID-19 adjunct role has mixed and uncertain evidence across published trials; the previously cited systematic review PMID (34375847) was confirmed as an entity mismatch and has been removed; no replacement COVID-19 systematic review citation is added to this record per implementation rules. The previously cited acetaminophen landmark PMID (2680050), OCD citation PMID (16640009), and COVID review PMID (34375847) were all confirmed as entity mismatches and have been removed. Long-term oral supplementation safety is well-characterized across decades of use. FDA-labeled IV dosing is distinct from oral supplementation dosing contexts.

Research Areas

  • Antioxidant & glutathione precursor
  • Liver protection & acetaminophen overdose
  • COPD & mucolytic
  • OCD & psychiatric
  • Addiction treatment
  • COVID-19 (adjunct, emerging)

Safety & Risks

Serious Risks

  • IV administration: anaphylactoid reactions (rare, ~0.2%); high-dose IV: hypotension; very high oral doses: GI toxicity

Reported Side Effects

  • Nausea/vomiting (especially at higher doses)
  • Rotten egg odor (sulfur smell)
  • Diarrhea
  • Skin rash
United States
FDA-approved for IV acetaminophen overdose treatment (Acetadote, NDA 018829) and as a mucolytic for COPD and cystic fibrosis. Oral NAC is widely marketed as a supplement; the FDA maintains that NAC is excluded from the statutory dietary supplement definition under FDCA 201(ff)(3)(B) because it was approved as a drug before evidence of prior food or supplement marketing was established. FDA's 2022 enforcement discretion guidance establishes that FDA will exercise discretion for certain NAC-containing products marketed as dietary supplements that would otherwise be lawful under the FDCA. FDA has not reversed the statutory exclusion.
United Kingdom
Prescription (Parvolex IV); OTC as supplement
Australia
OTC supplement / Schedule 4 for IV formulation
Canada
OTC supplement / Prescription (IV)

Citations & Sources