N-Acetylcysteine (NAC)
Also known as: NAC, N-Acetyl-L-cysteine, Acetylcysteine, Mucomyst, Acetadote, Fluimucil
Mucolytic | Glutathione Precursor | FDA-Approved Drug
Overview
N-acetylcysteine (NAC) is the acetylated form of the amino acid L-cysteine and the rate-limiting precursor to glutathione, the body's principal endogenous antioxidant. NAC has been a prescription drug for several decades — most notably as a mucolytic (Mucomyst) for cystic fibrosis and COPD, and as an IV antidote (Acetadote) for acetaminophen overdose, where it remains the standard of care. It is also widely used as an over-the-counter supplement for liver support, antioxidant defence, and a growing list of investigational psychiatric applications including OCD, trichotillomania, and substance-use disorders. The supplement market for NAC has been turbulent — the FDA briefly contested its OTC status in 2020-2022 — but it is currently sold legally as a dietary supplement in the US and as a regulated drug in much of Europe and the UK. Mechanistically, NAC works as both a direct free-radical scavenger and as a substrate for glutathione synthesis; it also has independent effects on glutamatergic neurotransmission via the cystine-glutamate antiporter, which is the basis for its psychiatric applications.
Key benefits
- Replenishes hepatic glutathione, supporting liver detoxification capacity
- FDA-approved standard of care for acetaminophen overdose (IV form)
- Mucolytic effects useful in COPD, cystic fibrosis, and acute respiratory illness
- Reduces oxidative stress markers in clinical trials (MDA, F2-isoprostanes)
- Emerging evidence for OCD, trichotillomania, and skin-picking disorders
- May reduce craving and relapse in alcohol- and cocaine-use disorders
- Modest cardioprotective effects via reduction of homocysteine and oxidative LDL
- Generally well-tolerated with a wide therapeutic window
Mechanism of action
NAC's primary mechanism is supplying cysteine — the rate-limiting amino acid for glutathione (GSH) synthesis. Once absorbed, NAC is rapidly deacetylated to cysteine in the gut wall and liver, raising intracellular cysteine pools and driving GSH synthesis via γ-glutamylcysteine synthetase. Glutathione is the principal endogenous antioxidant in nearly every tissue, particularly important in hepatocytes (acetaminophen detoxification), red blood cells, and neurons. Beyond the GSH pathway, NAC has a free thiol group that directly reduces reactive oxygen species. In acetaminophen overdose, NAC replenishes GSH stores depleted by the toxic metabolite NAPQI, preventing hepatocyte necrosis. As a mucolytic, NAC's free thiol cleaves disulfide bonds in mucin glycoproteins, reducing mucus viscosity. In the CNS, NAC modulates the cystine-glutamate antiporter (system Xc-), which exchanges extracellular cystine for intracellular glutamate. The resulting elevation of extracellular glutamate appears to dampen pathological glutamatergic signalling in conditions like OCD and addiction — the basis for NAC's growing psychiatric evidence base.
Molecular data
- Type
- Acetylated cysteine derivative (C5H9NO3S)
- Half-life
- ~6 hours (oral); plasma cysteine elevation persists ~12 hours
Indications
What the research community uses this compound for, with self-reported effectiveness.
Liver & Detoxification
Respiratory
Mental Health
Antioxidant / Cellular
Dosing protocols
Common protocols by delivery method. Adjust the curve below to model accumulation in your own cycle.
Oral
Bioavailability: ~10% systemic (low — most is taken up by gut and liver, where its main effect is required)Sulfur smell is normal. Effervescent forms are best tolerated; capsules with food work for sensitive stomachs.
| Protocol | Dose | Frequency | Duration |
|---|---|---|---|
| General antioxidant / liver support | 600 mg | 1-2x daily | Ongoing |
| OCD or trichotillomania adjunct | 2400-3000 mg | Split into 2-3 doses daily | Minimum 12 weeks for evaluation |
| COPD adjunct | 1200-1800 mg | 2-3x daily | Ongoing |
Intravenous
Bioavailability: 100% (hospital use only)IV protocol for acetaminophen overdose — administered in emergency departments, not relevant to outpatient supplementation.
Safety
Reported adverse effects, contraindications, and what to monitor on cycle.
Common side effects
- Sulfur taste/smell (the compound itself)
- Mild GI upset (nausea, loose stools), especially at >1200 mg single dose
- Headache (uncommon at OTC doses)
Uncommon side effects
- Diarrhoea or vomiting at high doses
- Anaphylactoid reaction with IV administration (not oral)
Rare side effects
- Bronchospasm with inhaled NAC in asthmatic patients
- Skin rash
Contraindications
- Active asthma exacerbation (relative contraindication for inhaled NAC; oral is fine)
Monitoring
- None required for typical supplemental doses. High-dose psychiatric protocols — check liver enzymes annually as a baseline practice.
Featured in these stacks
- Liver & Detox SupportAn antioxidant liver-support stack pairing injectable glutathione with its precursor NAC.2 compounds
- Neuro Focus (Semax)A neuroprotective focus stack built on the Semax family, with NAC as an antioxidant support.2 compounds
- Wakefulness & FocusA daytime-alertness stack pairing modafinil with NAC — for focus and wakefulness on demanding days.2 compounds