N-Acetylcysteine (NAC)
N-acetylcysteine (NAC) is both a medicine and a supplement ingredient. See how it differs from true amino acids, its US legal status, what trials show, and safety points.
Content last updated . This page has not been medically reviewed.
What is N-acetylcysteine good for?
What the body uses it for, and how strong the evidence is. A normal job in the body is not proof that extra supplements add benefit; each card says which.
Antidote for paracetamol (acetaminophen) overdose
Clinically supportedHospitals give acetylcysteine as a medicine to people at risk of liver damage from a paracetamol overdose. This is emergency medical care, not a supplement use.
Supplements: This is a hospital medicine given by clinicians. Supplements are not a substitute; an overdose is an emergency even if the person feels well.
Thinning mucus in chronic lung disease (mucolytic)
Preliminary or mixedAcetylcysteine is used as a medicine to loosen thick mucus in lung conditions. A Cochrane review of oral mucolytics (NAC among them) found a small benefit for flare-ups in chronic bronchitis and COPD.
Supplements: Results are mixed: smaller effects in newer studies, and the evidence is not specific to NAC supplements.
Adding to usual care for depression
Preliminary or mixedA 2024 meta-analysis of 12 trials found a small improvement in depression scores when NAC was added to usual care, with a wide margin of uncertainty.
Supplements: Promising but limited; the authors call for larger trials. It is an add-on, not a replacement for treatment.
Source of cysteine for making glutathione
Lab or animal research onlyThe body needs cysteine and glycine to make glutathione, one of its own antioxidants. NAC is a derivative of cysteine, and the body can make cysteine itself.
Supplements: In a trial in 114 healthy older adults, glycine plus NAC for 2 weeks did not raise the main glutathione measure overall; only a post-hoc subgroup with high oxidative stress and low glutathione did. Normal-biology or lab antioxidant activity is not proof that taking NAC as a supplement helps.
Antioxidant activity (laboratory chemistry)
Lab or animal research onlyNAC contains a sulphur group that can react with reactive molecules in the lab, so it is called an antioxidant.
Supplements: No source read shows that this lab activity prevents disease or slows ageing in healthy people. Normal-biology or lab antioxidant activity is not proof that taking NAC as a supplement helps.
Supplement versus drug status
Not enough evidenceIn the US the FDA treats NAC as excluded from the dietary supplement definition, because it was approved as a drug first, but it has a policy of enforcement discretion for certain NAC products. Other countries differ.
Supplements: Not a health benefit. The FDA said its initial review found no safety concerns, and its safety review was going to peer review as of November 2023.
Connected topics
Open a group to see how each topic connects and how strong the evidence is.
Health goals (1)
- Mood BalancePreliminary or mixed
Added to usual care, NAC gave a small improvement in depression scores in a 2024 meta-analysis; larger trials are needed. Not a replacement for treatment.
Body systems (3)
- Hepatic / Liver SystemClinically supported
Acetylcysteine is a hospital antidote for paracetamol overdose, given by clinicians. Supplements are not a substitute, and evidence for liver benefit in healthy people was not found.
- Respiratory HealthPreliminary or mixed
Acetylcysteine is used as a medicine to thin mucus, and a Cochrane review of oral mucolytics (NAC among them) found a small benefit for flare-ups in chronic bronchitis and COPD, with smaller effects in newer studies. Not specific to supplements.
- Respiratory SystemPreliminary or mixed
Acetylcysteine is used as a medicine to thin mucus, and a Cochrane review of oral mucolytics (NAC among them) found a small benefit for flare-ups in chronic bronchitis and COPD, with smaller effects in newer studies. Not specific to supplements.
Body parts (2)
- LiverClinically supported
Acetylcysteine is a hospital antidote for paracetamol overdose, given by clinicians. Supplements are not a substitute, and evidence for liver benefit in healthy people was not found.
- LungsPreliminary or mixed
Acetylcysteine is used as a medicine to thin mucus, and a Cochrane review of oral mucolytics (NAC among them) found a small benefit for flare-ups in chronic bronchitis and COPD, with smaller effects in newer studies. Not specific to supplements.
Functional actions (4)
- AntioxidantLab or animal research only
NAC supplies cysteine, which the body uses to make the antioxidant glutathione. In healthy older adults, glycine plus NAC did not raise the main glutathione measure overall. Normal-biology or lab antioxidant activity is not proof that taking NAC as a supplement helps.
- Liver SupportClinically supported
Acetylcysteine is a hospital antidote for paracetamol overdose, given by clinicians. Supplements are not a substitute, and evidence for liver benefit in healthy people was not found.
- Respiratory SupportPreliminary or mixed
Acetylcysteine is used as a medicine to thin mucus, and a Cochrane review of oral mucolytics (NAC among them) found a small benefit for flare-ups in chronic bronchitis and COPD, with smaller effects in newer studies. Not specific to supplements.
- Mood SupportPreliminary or mixed
Added to usual care, NAC gave a small improvement in depression scores in a 2024 meta-analysis; larger trials are needed. Not a replacement for treatment.
Root causes (1)
- Oxidative StressPreliminary or mixed
In one trial of glycine plus NAC, glutathione rose only in a post-hoc subgroup with high oxidative stress and low glutathione. This is preliminary and from a single study.
Conditions & symptoms (5)
- Bronchitis, ChronicPreliminary or mixed
Same Cochrane review: mucolytics probably make people somewhat more likely to be free of flare-ups.
- Chronic Obstructive Airway DiseasePreliminary or mixed
A Cochrane review of oral mucolytics (NAC among them) found a small benefit for flare-ups; effects were smaller in recent trials.
- Cystic FibrosisClinically supported
MedlinePlus lists cystic fibrosis among conditions where inhaled acetylcysteine is used with other treatments to loosen thick mucus. This is a medicine use, not a supplement use.
- Depression, BipolarPreliminary or mixed
The meta-analysis authors noted the benefit may be clearer in bipolar disorder; evidence is limited.
- Mental DepressionPreliminary or mixed
Small improvement as an add-on in a 2024 meta-analysis; larger trials needed.
Documented risks and interactions (2)
- Side effects of oral NAC at high amounts. In a review of studies of chronic lung disease (600 to 3,000 mg a day), stomach and bowel symptoms were reported but were no more common than with comparison treatment.
- Side effects of inhaled acetylcysteine and asthma caution. MedlinePlus lists nausea, vomiting, throat irritation and drowsiness among possible effects of the inhaled medicine, and wheezing or chest tightness as serious ones. People with asthma should tell their doctor.
Urgent point first
An acetaminophen (paracetamol) overdose is an emergency, even if the person feels fine. In the US call 911 or Poison Help at 1-800-222-1222; for other countries see poison help by country. Hospitals give acetylcysteine as a medicine for this; supplements are not a substitute. Cochrane reviewers concluded acetylcysteine should be given to people at risk of toxicity. [1]Quick answer
N-acetylcysteine, usually called NAC, is a derivative of the amino acid cysteine. It is not one of the building-block amino acids that make up protein, and it is not essential. MedlinePlus lists cysteine itself among the nonessential and conditionally essential amino acids, meaning it is usually made by the body but may be needed in illness and stress. [2]NAC is both a long-established medicine and a supplement ingredient. This page covers the supplement side and keeps it apart from medicine use. It is also featured under antioxidants and specialty compounds; related pages are glutathione and cysteine, cystine and glutathione precursor claims.
Evidence by use
Labels: established medical use (an approved treatment given by clinicians), mixed, promising but limited, and insufficient evidence.| Use | What the sources found | Label |
|---|---|---|
| Acetaminophen overdose (hospital care) | A Cochrane review found acetylcysteine appeared superior to placebo and had fewer adverse effects than dimercaprol or cysteamine, but trials were small and all were at high risk of bias. [1] | Established medical use, given by clinicians |
| COPD and chronic bronchitis (mucus-thinning medicines) | A Cochrane review of 38 trials (10,377 people) of several mucolytics, NAC among them, found people on mucolytics were more likely to be free of flare-ups, although more recent studies showed less benefit than earlier ones. [5] | Mixed; not specific to supplements |
| Depression added to usual care | A 2024 meta-analysis of 12 trials (904 people; 1,000 to 3,000 mg a day for 8 to 24 weeks) found a small improvement in depression scores and called for large trials. [6] | Promising but limited |
| Raising glutathione in healthy older adults | In a trial of 114 healthy volunteers, glycine plus NAC for 2 weeks did not raise the main glutathione measure; a post-hoc subgroup with high oxidative stress and low glutathione did show an increase. [7] | Insufficient evidence in healthy people |
| Fertility, polycystic ovary syndrome, "detox", liver or lung wellness in healthy people | Proper evidence not found: none of the reviews and trials we read address these, so no claim is made. | Insufficient evidence |
The glycine plus NAC trial included employees of a company that markets products using that combination. [7]
Amounts and official limits
Amounts in studies are study amounts, not advice. Depression trials used 1,000 to 3,000 mg a day. [6] A 2021 review said the maximum licensed dose in chronic respiratory use was 600 mg a day, while trials had tested up to 3,000 mg a day. [8] No official recommended intake or upper limit for NAC as a supplement was found in the sources we read.Labels and quality
Look for a clear NAC amount per serving and independent testing; see reading supplement labels and quality testing and certifications. A product that promises to "boost glutathione" or treat a disease is making a claim the sources above do not support.Frequently asked questions
Is NAC an amino acid?
It is a derivative of the amino acid cysteine, not one of the amino acids that build proteins. Cysteine is classed as conditionally essential. [2]
Is NAC a drug or a supplement?
Both. Acetylcysteine is a hospital medicine for acetaminophen overdose. [1] In the US the FDA says NAC is excluded from the dietary supplement definition but has a policy of enforcement discretion for certain products. [3]
Does NAC raise glutathione?
In one trial in healthy older adults, glycine plus NAC did not raise the main glutathione measure, though a subgroup with high oxidative stress did show an increase. [7]
Does NAC help depression?
A 2024 meta-analysis found a small improvement as an add-on in people with depression, and called for larger trials. [6]
Is NAC safe?
In studies of chronic lung disease, stomach and bowel symptoms were no more common than with comparison treatment. [8] Ask a clinician or pharmacist first if you take medicines, are pregnant or have liver or kidney conditions.
More details: evidence, limits and cautions
The details behind this page: cautions, limits of the evidence and where sources disagree. Open any note to read it.
Legal status in the United States
Side effects, medicines and who should ask first
- Stomach and bowel symptoms. In studies of chronic lung disease, these were reported with oral NAC but were no more common than in the control groups, at standard and higher doses. [8] That analysis was sponsored by a pharmaceutical company. [8]
- Long-term use in healthy people. Not well documented in the sources we read, and the FDA described its review as going to peer review. [3]
- Inhaled acetylcysteine. MedlinePlus lists nausea among its possible side effects and asks people to tell their doctor if they are pregnant, planning pregnancy or breastfeeding. [9] That page covers the inhaled medicine, not supplements.
- Interactions with other medicines, pregnancy, children, kidney or liver disease, and surgery. For supplements these are not described in the sources we read. Talk to a clinician or pharmacist. See how interactions work, pregnancy and breastfeeding, liver safety and supplements before surgery.
References
- Chiew AL et al. Interventions for paracetamol (acetaminophen) overdose. Cochrane Database Syst Rev 2018. Read 2026-10-22.
- MedlinePlus. Amino acids. National Library of Medicine, US (reviewed 1/21/2025). Read 2026-10-22.
- FDA. FDA Releases Final Guidance on Enforcement Discretion for Certain NAC Products. US Food and Drug Administration (updates dated 2022 and November 29, 2023). Read 2026-10-23.
- FDA. Guidance for Industry: Policy Regarding N-acetyl-L-cysteine. US Food and Drug Administration, August 2022. Read 2026-10-23.
- Poole P et al. Mucolytic agents versus placebo for chronic bronchitis or chronic obstructive pulmonary disease. Cochrane Database Syst Rev 2019. Read 2026-10-22.
- Peng TR et al. Efficacy of N-acetylcysteine for patients with depression: an updated systematic review and meta-analysis. Gen Hosp Psychiatry 2024. Read 2026-10-22.
- Lizzo G et al. A randomized controlled clinical trial in healthy older adults to determine efficacy of glycine and N-acetylcysteine supplementation on glutathione redox status and oxidative damage. Front Aging 2022. Read 2026-10-22.
- Calverley P et al. Safety of N-acetylcysteine at high doses in chronic respiratory diseases: a review. Drug Saf 2021. Read 2026-10-22.
- MedlinePlus. Acetylcysteine Oral Inhalation. MedlinePlus Drug Information, National Library of Medicine, US. Read 2026-10-23.