Mucolytic; paracetamol overdose antidote; glutathione precursor
ATC code: R05CB01 (Acetylcysteine)
Brand names
Cetylev, Mucomyst, Acetadote
In the body the acetyl group is cleaved and the molecule becomes L-cysteine – the rate-limiting substrate for glutathione synthesis. Glutathione binds the toxic paracetamol metabolite NAPQI and protects hepatocytes. Free SH groups break disulfide bonds between mucoprotein chains in sputum, which thins the secretion. The IV route delivers the maximum hepatic concentration; oral bioavailability is lower because of first-pass metabolism.
First line
First-line antidote for paracetamol overdose. AEMPS and approve oral and intravenous routes; maximum benefit when started within 8 hours of ingestion. IV Prescott protocol: 150 mg/kg over 1 hour, then 50 mg/kg over 4 hours, then 100 mg/kg over 16 hours. Efficacy declines after 10 hours but Cochrane 2018 shows benefit even with late initiation. The only NAC indication with tier A.
Adjunct
Add-on to SSRIs in treatment-resistant OCD and conditions with shared neurobiology (trichotillomania, excoriation disorder). Evidence base is limited: small randomised trials at 2400–3000 mg/day show weak signal. and AEMPS do not approve NAC for OCD; this use is off-label. The decision belongs to the psychiatrist after standard therapy fails. Before self-prescribing, consider seeking a second medical opinion.
Sources
Individual decision
Mucolytic for productive cough with thick sputum. AEMPS keeps acetylcysteine indicated, but the clinical effect is modest: systematic reviews show cough duration reduced by about 0.5 days vs placebo. In cystic fibrosis, Cochrane 2013 did not confirm benefit from oral NAC. In common colds a 5–10 day course is appropriate. If cough persists beyond 7–10 days or dyspnoea appears, in-person evaluation is required.
The drug is promoted for these uses outside international guidelines. Each entry below is analyzed against AEMPS, FDA, EMA, Cochrane and major RCTs.
Not recommended
Acetylcysteine is a mucolytic that thins mucus, and in high intravenous doses it works as an antidote for paracetamol poisoning. It is often marketed as a supplement for "liver support" and liver protection in healthy people. There is no convincing benefit for this use: the evidence that regular intake protects the liver or improves its function outside paracetamol overdose is lacking. What actually helps liver health is avoiding alcohol, keeping a healthy weight, hepatitis vaccination, and treating any underlying condition with your doctor. Do not take acetylcysteine instead of treatment with proven benefit – that can mean missing the care you need.
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FDA Category B. Crosses the placenta but no teratogenicity has been documented. AEMPS permits indicated use, particularly in pregnant paracetamol overdose where maternal benefit outweighs risk.
Compatible. Hale L2. Milk transfer data are limited, but with short courses and standard doses no infant adverse events have been reported. eLactancia rates the risk as low.
Acetylcysteine is evaluated for the following indications with varying evidence strength: Paracetamol overdose (evidence tier A), Obsessive-compulsive disorder (evidence tier C), Productive cough with thick sputum (evidence tier C). See the full indication matrix with dosing and citations above on this page.
Common side effects of Acetylcysteine (≥ 1 in 100): Nausea, vomiting, heartburn, Diarrhoea, Unpleasant sulphurous breath, Rash and pruritus. See the Safety section for uncommon and serious reactions.
FDA category B. FDA Category B. Crosses the placenta but no teratogenicity has been documented. AEMPS permits indicated use, particularly in pregnant paracetamol overdose where maternal benefit outweighs risk.
Compatible. Hale L2. Milk transfer data are limited, but with short courses and standard doses no infant adverse events have been reported. eLactancia rates the risk as low.
Acetylcysteine is contraindicated in: Hypersensitivity to acetylcysteine; Active peptic ulcer disease; Haemoptysis and pulmonary haemorrhage. Full list in the Safety section.
Not recommended
Biohacker community frames NAC as an «anti-aging drug», «universal antioxidant» and «mitochondrial protector». There are no long-term randomised trials in healthy people with mortality or age-related disease endpoints. NIH ODS 2024 notes that benefit in healthy adults is unproven; in animal models antioxidant excess even accelerated tumour growth. AEMPS and have not registered the drug as a geroprotector. For evidence-based prevention of ageing, lifestyle, sleep, physical activity and diet – confirmed in large cohorts – are appropriate topics to discuss with a clinician.
Reference information, not a clinical decision. Discuss feeding pauses or changes with your physician or an IBCLC.