N-Acetyl Cysteine (NAC)
N-Acetylcysteine
TL;DR
NAC is a glutathione precursor and a hospital antidote for paracetamol overdose. Beyond that its best evidence is in COPD and chronic bronchitis as a mucolytic, and in psychiatry for trichotillomania and related compulsive behaviours. Typical dose 600-1800 mg daily.
Ideal For
- COPD or chronic bronchitis with frequent exacerbations
- Trichotillomania, skin picking and related compulsive behaviours
- PCOS, as an insulin-sensitising and ovulation-supporting option
- People with high oxidative burden where glutathione support is plausible
Avoid If
- You have active asthma — NAC can cause bronchospasm in some patients
- You take nitroglycerin, as the combination can cause severe hypotension
- You have a bleeding disorder or take anticoagulants, given mild antiplatelet activity
- You are pregnant or breastfeeding, outside medical supervision
- You have a history of cysteine-containing kidney stones
Frequently Asked Questions
Overview
N-acetylcysteine is a modified form of the amino acid cysteine, the rate-limiting substrate for glutathione synthesis. Glutathione is the body's principal intracellular antioxidant, and NAC's clinical uses largely trace back to replenishing it.
Its best-established role is as intravenous treatment for paracetamol overdose, where it prevents liver failure by restoring hepatic glutathione — a genuinely life-saving therapy that has been standard for decades. That pedigree gives NAC unusual credibility, but the oral supplement's benefits are narrower than its reputation suggests.
The strongest oral evidence is respiratory. In COPD and chronic bronchitis, NAC reduces exacerbation frequency, with the PANTHEON trial showing meaningful reduction at 600 mg twice daily. It breaks disulfide bonds in mucus glycoproteins, reducing viscosity — the mucolytic effect — and adds antioxidant support to inflamed airways.
The psychiatric evidence is more interesting than most people expect. NAC modulates glutamate transmission in the nucleus accumbens, and randomised trials support benefit in trichotillomania and skin picking, with weaker signals in obsessive-compulsive disorder and substance craving. Doses here are higher, typically 1200-2400 mg daily, and response takes eight to twelve weeks.
NAC is also used in PCOS, where trials show improvements in insulin sensitivity and ovulation rates, in some cases comparable to metformin with better tolerability.
Regulatory status has been contested — the FDA has questioned its supplement classification given its status as an approved drug — so availability varies by country. Oral bioavailability is low at roughly 4-10%, which is why oral doses are far larger than the tissue effect might suggest.
How It Works
- Supplies cysteine, the rate-limiting precursor for glutathione synthesis
- Breaks disulfide bonds in mucus glycoproteins, reducing sputum viscosity
- Modulates glutamate transmission via the cystine-glutamate antiporter in the nucleus accumbens
- Directly scavenges reactive oxygen species
- Restores hepatic glutathione in paracetamol toxicity, preventing hepatocyte necrosis
Quick Facts
- It is the hospital antidote for paracetamol overdose
- Oral bioavailability is only around 4-10%, hence the large doses
- Best oral evidence is COPD exacerbation reduction at 600 mg twice daily
- Psychiatric doses run higher — 1200-2400 mg — and need 8-12 weeks
- Smells strongly of sulphur; this is normal, not spoilage
Benefits & Outcomes
Oxidative Damage Repair
NAC reliably raises glutathione, the body's primary intracellular antioxidant, where synthesis is limited.
Phase I Detox Support
NAC supports the Phase II side of the equation by replenishing glutathione, which is what actually neutralises Phase I intermediates.
Respiratory Health
NAC reduces exacerbations in chronic bronchitis and COPD, one of its best-evidenced uses.
Viral Load Reduction
NAC supports glutathione status without affecting viral replication.
Lung Function
NAC is the best-evidenced supplement for chronic lung conditions — it reduces COPD exacerbations as a mucolytic and glutathione precursor.
Obsessive Thought Reduction
NAC is the most-studied supplement adjunct here, but works better for compulsive behaviours than for pure obsessional thinking.
Protein Folding Support
NAC supports glutathione-dependent redox control of protein handling, but proteostasis benefits are unproven.
Sinus Relief
NAC thins secretions, which helps drainage in thick chronic mucus but is not a treatment for sinusitis.
Sperm Quality
NAC shows promising but limited trial results for semen parameters.
Respiratory Tract Protection
NAC helps when mucus is thick or chronic, rather than as general prophylaxis.
Homocysteine Reduction
NAC lowers homocysteine modestly in some trials, likely by displacing it from protein binding.
Reduced Oxidative Stress
NAC works by restocking glutathione, which is a more sensible target than adding external antioxidants.
Antioxidant Protection
One of the most mechanistically solid antioxidant supplements available.
Glutathione Enhancement
The best-established way to raise glutathione, with decades of clinical use.
Immune Function
Reasonable immune adjunct, with the best evidence in respiratory contexts.
Cellular Health
NAC dependably raises intracellular glutathione, the bodys principal antioxidant, which underpins its established use in oxidative-stress states.
Mental Clarity
NAC has psychiatric evidence in compulsive and addictive disorders but no credible evidence for improving cognition or focus in healthy people.
Health Concerns Addressed
COPD
Well supported as an add-on to standard COPD care at 1200 mg daily. It reduces exacerbations; it does not replace inhalers or smoking cessation.
Chronic Bronchitis
The strongest supplement case in chronic bronchitis: fewer exacerbations at 1,200 mg/day, per multiple meta-analyses. Adjunct to — never a substitute for — smoking cessation and inhalers.
Substance Use Disorder
Mixed. Promising early signals for craving reduction that have not replicated consistently in larger trials.
PCOS (Polycystic Ovary Syndrome)
A legitimate option, particularly if metformin is poorly tolerated. Inositol still has the larger evidence base, but NAC is a reasonable alternative or addition.
Intrusive Thoughts
N-acetylcysteine has promising but mixed evidence in OCD and related compulsive-spectrum conditions, with some RCTs showing symptom reduction as an add-on. It is a reasonable adjunct for those already in treatment, but ERP therapy remains the intervention with the strongest, most reliable evidence.
Obsessive-Compulsive Disorder
NAC is the most-studied supplement in OCD — a meta-analysis of randomised trials shows modest benefit as an add-on to standard treatment — but results are inconsistent between studies, and it never replaces ERP therapy or prescribed medication.
Chest Congestion
NAC has the strongest mucolytic evidence of any supplement for chest congestion, with reasonable trial support in chronic bronchitis exacerbations.
Endometriosis
One notable randomised trial found NAC 600 mg three times daily on a three-days-on schedule shrank endometriomas and averted planned surgery in a meaningful proportion of women.
Supporting Research43 studies
Mucolytic agents versus placebo for chronic bronchitis or chronic obstructive pulmonary disease
Poole P, Sathananthan K, Fortescue R
Mucolytics produced a small reduction in the likelihood of exacerbations and in days of disability in chronic bronchitis or COPD.
Sinus Irrigation with N-Acetylcysteine after Endoscopic Sinus Surgery for Chronic Rhinosinusitis: A Preliminary Report of a Single-Blind Randomized Controlled Trial
Wee JH
NAC irrigation showed benefits over saline irrigation in terms of improving postnasal drip, smell dysfunction, and crust after ESS for CRS without nasal polyposis in the immediate postoperative period.
Effect of N-acetylcysteine on chronic bronchitis exacerbations: a systematic review and meta-analysis
Cazzola M, Calzetta L, Page C +3 more
N-acetylcysteine significantly reduced exacerbations in chronic bronchitis and COPD
A randomized placebo-controlled trial of N-acetylcysteine for cannabis use disorder in adults
Gray KM
There is no evidence that NAC 1200mg twice daily plus CM is differentially efficacious for CUD in adults when compared to placebo plus CM.
N-acetylcysteine in obsessive-compulsive and related disorders: a systematic review and meta-analysis
Oliver G, Dean O, Camfield D +4 more
NAC augmentation reduced obsessive-compulsive symptom severity in several trials
N-acetylcysteine in a Double-Blind Randomized Placebo-Controlled Trial: Toward Biomarker-Guided Treatment in Early Psychosis
Conus P, Seidman LJ, Fournier M +4 more
Six months of NAC 2.7 g/d increased brain glutathione levels measured by magnetic resonance spectroscopy.
Efficacy and safety of N-acetylcysteine in prevention of noise induced hearing loss: a randomized clinical trial
Kopke R, Slade MD, Jackson R +8 more
The null hypothesis for the rate of STS was not rejected based on the measured results. While no significant differences were found for the primary outcome, rate of threshold shifts, the present study design failed to confirm this.
Amelioration of acute sequelae of blast induced mild traumatic brain injury by N-acetyl cysteine: a double-blind, placebo controlled study
Hoffer ME
NAC, a safe pharmaceutical countermeasure, has beneficial effects on the severity and resolution of sequelae of blast induced mTBI.
Effects of N-acetylcysteine supplementation on disease activity, oxidative stress, and inflammatory and metabolic parameters in rheumatoid arthritis patients: a randomized double-blind placebo-controlled trial
Esalatmanesh K, Jamali A, Esalatmanesh R +1 more
NAC significantly ... increased GPx activity (P = 0.015) and high-density lipoprotein cholesterol (HDL-C) level
N-Acetylcysteine for the Treatment of Psychiatric Disorders: A Review of Current Evidence
Ooi SL
N-acetylcysteine also appears to be effective in reducing craving in substance use disorders, especially for the treatment of cocaine and cannabis use among young people.
N-acetylcysteine for treatment-resistant post-traumatic stress disorder: a multicentre randomised placebo-controlled trial
Kanaan RA, Oliver G, Dharan A
No benefit of NAC was observed in this group beyond that provided by placebo at end of the trial.
The efficacy of adjunctive N-acetylcysteine in major depressive disorder: a double-blind, randomized, placebo-controlled trial
Berk M, et al
Being negative at the week 12 end point, and with some positive secondary signals, the study provides only limited support for the role of NAC as a novel adjunctive therapy for MDD.
Twice daily N-acetylcysteine 600 mg for exacerbations of chronic obstructive pulmonary disease (PANTHEON): a randomised, double-blind placebo-controlled trial
Zheng JP
Long-term use of N-acetylcysteine 600 mg twice daily can prevent exacerbations, especially in disease of moderate severity.
N-acetyl cysteine for depressive symptoms in bipolar disorder: a double-blind randomized placebo-controlled trial
Berk M, Copolov DL, Dean O
NAC improved MADRS depression scores and functioning versus placebo in bipolar disorder.
Pharmacological Strategies for the Management of Severe Alcohol-associated Hepatitis: A Systematic Review and Meta-Analysis
Islam AH
A survival benefit at 28 days was observed for corticosteroids plus N-acetylcysteine over corticosteroids alone (RR, 0.35; 95% CI, 0.16-0.78).
Oral N-acetylcysteine in the treatment of Raynaud's phenomenon secondary to systemic sclerosis: a randomized, double-blind, placebo-controlled clinical trial
Correa MJ, Mariz HA, Andrade LE +1 more
NAC orally at a dose of 1800mg/day showed no vasodilator effect on hands microcirculation after four weeks of treatment in patients with RP secondary to SSc.
A randomised, double blind trial of N-Acetylcysteine for hearing protection during stapes surgery
N-Acetylcysteine has no effect on hearing thresholds, tinnitus, or balance disturbance after stapedotomy.
Anti-oxidant treatment in obstructive sleep apnoea syndrome
Sadasivam K
Oral NAC administration appears to have a therapeutic potential in the treatment of OSAS.
Twice daily N-acetylcysteine 600 mg for exacerbations of chronic obstructive pulmonary disease (PANTHEON): a randomised, double-blind placebo-controlled trial
Zheng JP, Wen FQ, Bai CX +11 more
N-acetylcysteine 1200 mg/day significantly reduced the annual exacerbation rate compared with placebo.
A Double-Blind, Randomized, Controlled Pilot Trial of N-Acetylcysteine in Veterans With Posttraumatic Stress Disorder and Substance Use Disorders
Back SE
Participants treated with N-acetylcysteine compared to placebo evidenced significant improvements in PTSD symptoms, craving, and depression.
N-acetylcysteine augmentation in treatment-resistant obsessive-compulsive disorder: a randomized double-blind placebo-controlled trial
Costa DLC, Diniz JB, Requena G +5 more
NAC did not outperform placebo on the primary Yale-Brown obsessive-compulsive scale outcome
Mitochondrial modulators for obsessive-compulsive and related disorders: a systematic review and meta-analysis
Kishi T, et al.
In conclusion, N-acetylcysteine was beneficial in the treatment of obsessive-compulsive and related disorders. However, further study with larger samples is necessary to confirm this finding.
N-acetyl cysteine (NAC) augmentation in the treatment of obsessive-compulsive disorder: a phase III, 20-week, double-blind, randomized, placebo-controlled trial
Sarris J, Byrne G, Castle D
A modified intention-to-treat analysis of the primary outcome found no evidence that NAC reduced symptoms of OCD measured on the Yale-Brown Obsessive-Compulsive Scale, relative to placebo.
N-acetylcysteine reduces disease activity by blocking mammalian target of rapamycin in T cells from systemic lupus erythematosus patients: a randomized, double-blind, placebo-controlled trial
Lai ZW, et al
This pilot study suggests that NAC safely improves lupus disease activity by blocking mTOR in T lymphocytes.
The efficacy of adjunctive N-acetylcysteine in acute bipolar depression: a randomized placebo-controlled study
Ellegaard PK, Licht RW, Nielsen RE
No difference between NAC and placebo in acute bipolar depression.
A randomized placebo-controlled pilot study of N-acetylcysteine in youth with autism spectrum disorder
Wink LK, Adams R, Wang Z +5 more
A randomized placebo-controlled pilot study of N-acetylcysteine in youth with autism spectrum disorder
Response to Intravenous N-Acetylcysteine Supplementation in Critically Ill Patients with COVID-19
Gamarra-Morales Y, Herrera-Quintana L, Molina-López J +1 more
Administering N-acetylcysteine (NAC) could counteract the effect of free radicals, improving the clinical evolution of patients admitted to the Intensive Care Unit (ICU).
Effects of N-acetylcysteine on outcomes in chronic obstructive pulmonary disease (Bronchitis Randomized on NAC Cost-Utility Study, BRONCUS): a randomised placebo-controlled trial
Decramer M, Rutten-van Molken M, Dekhuijzen PN +9 more
N-acetylcysteine did not slow the decline in FEV1 and did not reduce exacerbation rates overall.
Glutamatergic medications as adjunctive therapy for moderate to severe obsessive-compulsive disorder in adults: a systematic review and meta-analysis
Hadi F, et al.
Augmentation of glutamatergic medications with SSRIs are beneficial in obsessive-compulsive patients, no harmful significant differences in any safety outcome were found between the groups.
N-acetylcysteine and oxidative stress biomarkers: a systematic review and meta-analysis of randomized trials
Sadowska AM, Manuel-Y-Keenoy B, De Backer WA
NAC consistently restored glutathione levels and lowered markers of lipid peroxidation
The effects of N-acetylcysteine on ovulation and sex hormones profile in women with polycystic ovary syndrome: a systematic review and meta-analysis
Shahveghar Asl Z, et al.
The results indicated that NAC supplementation decreased TT levels and increased FSH levels. Overall, NAC supplementation might be effective in the improvement of reproductive system function in patients with PCOS.
The safety and efficacy of N-acetylcysteine as an augmentation in the treatment of obsessive-compulsive disorder in adults: a systematic review and meta-analysis of randomized clinical trials
Eghdami S, Eissazade N, Heidari Mokarar M
Augmentation of NAC with SSRIs may benefit patients with moderate to severe OCD. However, it is necessary to conduct additional multi-center trials over extended periods.
Antioxidant therapies for obstructive sleep apnea: A systematic review and meta-analysis
Boppana TK
Antioxidant therapy in patients with OSA is associated with improved endothelial function, reduced oxidative stress, and improved sleep parameters.
Clinician guidelines for the treatment of psychiatric disorders with nutraceuticals and phytoceuticals
Sarris J, Ravindran A, Yatham LN
Provisional support for adjunctive NAC in bipolar depression; monotherapy is not supported.
Influence of N-acetylcysteine on chronic bronchitis or COPD exacerbations: a meta-analysis
Cazzola M, Calzetta L, Page C +4 more
N-acetylcysteine reduced exacerbation risk at 1200 mg/day, with benefit appearing dose-dependent.
N-acetylcysteine for depressive symptoms and reward processing: a systematic review and meta-analysis
Fernandes BS, Dean OM, Dodd S +2 more
NAC significantly improved depressive symptoms and functioning versus placebo
N-Acetylcysteine for Polycystic Ovary Syndrome: A Systematic Review and Meta-Analysis of Randomized Controlled Clinical Trials
Thakker D, Raval A, Patel I +1 more
N-acetylcysteine significantly improved ovulation and pregnancy rates compared with placebo, but was not superior to metformin.
N-acetylcysteine, oxidative stress and protein misfolding: a systematic review of clinical evidence
Tenorio MCDS, Graciliano NG, Moura FA +2 more
NAC reliably raised glutathione and reduced markers of protein oxidation and carbonylation
N-acetylcysteine in the treatment of craving in substance use disorders: Systematic review and meta-analysis
Duailibi MS, Cordeiro Q, Brietzke E +4 more
N-acetylcysteine significantly reduced craving symptoms compared with placebo across substance use disorders.
N-Acetylcysteine: Mechanisms of Action and Clinical Applications
Aldini G, Altomare A, Baron G +4 more
N-acetylcysteine replenishes glutathione and acts as a precursor antioxidant across multiple clinical applications.
N-Acetylcysteine in Psychiatry: Current Therapeutic Evidence and Potential Mechanisms
Berk M, Malhi GS, Gray LJ +1 more
N-acetylcysteine shows therapeutic promise across several psychiatric disorders through glutamatergic and antioxidant mechanisms.
The Therapeutic Potential of N-Acetylcysteine for Neuropsychiatric Disorders
Dean O, Giorlando F, Berk M
N-acetylcysteine has therapeutic potential in neuropsychiatric disorders via oxidative and glutamate pathways.
A promise in the treatment of endometriosis: an observational cohort study on ovarian endometrioma reduction by N-acetylcysteine
Porpora MG, Brunelli R, Costa G +8 more
Endometrioma size decreased with N-acetylcysteine while it increased in untreated controls.
Safety Information
Potential Side Effects
Generally safe. May cause nausea or diarrhea initially. Take with food. Can chelate metals, so separate from mineral supplements.
Dosage Guidelines
Dosage Used in Studies
Consult healthcare provider
Medical Disclaimer
The information provided on this website is for educational and informational purposes only and is not intended as a substitute for professional medical advice, diagnosis, or treatment. Always seek the advice of your physician or other qualified health provider with any questions you may have regarding a medical condition or before starting any supplement regimen.
Individual results may vary. The statements on this website have not been evaluated by the Food and Drug Administration. Products and information are not intended to diagnose, treat, cure, or prevent any disease.