Calculate N-acetylcysteine (NAC) dose by goal — liver support, cognitive, PCOS, mucolytic. RCT doses range from 600 mg to 2.4 g/day. The FDA-approved hospital protocol for paracetamol overdose is much higher (and requires immediate medical care). Math, not medical advice.
Your goal
600 mg, 2× daily
Target daily dose (typically split into 2 doses, with or without food)
Trial-derived doses
| Goal | Daily dose | Source trial |
|---|---|---|
| General antioxidant / glutathione | 600-1,200 mg | Standard maintenance; widely used |
| Liver support (chronic alcohol) | 1,200 mg (600 × 2) | Mardini 2010 systematic review |
| Cognitive / Alzheimer’s adjunct | 600-1,500 mg | Adair 2001 (mild AD), McCaddon 2003 |
| OCD adjunct | 2,400 mg (600 × 4) | Afshar 2012, Sarris 2015 |
| Trichotillomania | 1,200-2,400 mg | Grant 2009 double-blind RCT |
| PCOS / insulin sensitivity | 1,800 mg (600 × 3) | Fulghesu 2002, Oner 2011 |
| Male fertility / sperm motility | 600 mg/day | Safarinejad 2009 (testicular) |
| COPD / chronic bronchitis | 600-1,200 mg | BRONCUS 2005, PANTHEON 2014 |
| Pulmonary fibrosis adjunct | 1,800 mg | PANTHER-IPF 2014 (effect debated) |
| Hospital paracetamol overdose (IV) | 140 mg/kg load + 70 mg/kg q4h | Mucomyst FDA-approved protocol |
How NAC actually works
- NAC is a precursor to glutathione, the body’s master antioxidant. The body cannot directly supplement glutathione orally (it’s degraded in gut). NAC provides the rate-limiting amino acid (cysteine) for endogenous glutathione synthesis.
- For paracetamol overdose, NAC replenishes glutathione to detoxify the toxic NAPQI metabolite. Time-critical — most effective within 8-10 hours of overdose. This is why ER care matters, not supplements.
- For pulmonary use, NAC has direct mucolytic effect (breaks disulfide bonds in mucus). Original FDA-approved indication.
- For cognitive/psychiatric use, mechanism involves glutamate modulation in addition to glutathione effects.
- Bioavailability is modest (~10-20%) but adequate for most therapeutic goals at standard doses.
FDA status — what changed
In 2020, FDA sent warning letters to brands marketing NAC as a “dietary supplement,” arguing that NAC was first approved as a drug (Mucomyst) in 1963 and therefore excluded from DSHEA supplement classification. After significant industry pushback, FDA issued enforcement discretion in 2022 — NAC remains available as a supplement but the legal status is precarious. Most major brands continue selling it.
Side effects and drug interactions
- GI upset (nausea, sulfur-egg taste) is common — split doses with meals helps.
- Sulfur smell: NAC contains a sulfur group. Some people report sulfurous body odor or breath. Less noticeable with enteric-coated or effervescent forms.
- Nitroglycerin INTERACTION: NAC + nitrates can cause severe hypotension and headache. Avoid combination.
- Warfarin: modest INR increase reported in some patients. Monitor closely.
- Antibiotics: NAC may reduce efficacy of some antibiotics (tetracyclines, penicillin) — separate by 2 hours.
- Pregnancy: NAC IS used IV during pregnancy for paracetamol overdose. Limited safety data for routine oral supplementation; defer to obstetrician.
- Asthma: rare bronchospasm reported with high-dose NAC, especially in asthmatics. Start at lower dose if asthmatic.
- Bleeding risk: mild antiplatelet activity at high doses. Discontinue 1-2 weeks before surgery.