N-acetylcysteine

N-acetyl-L-cysteine (NAC) · also called NAC, acetylcysteine, N-acetilcisteina

N-acetylcysteine (NAC) is a modified form of the amino acid cysteine. It is a hospital medicine for paracetamol overdose and for thinning mucus, and it is also sold as a supplement. Evidence is firmest for those medicine uses; for depression, COPD flare-ups and fertility it is mixed or low-certainty, and it did not help in pulmonary fibrosis or kidney protection. A paracetamol overdose is an emergency: pills are not a substitute for hospital care.

General information, not medical advice. Last substantive update October 26, 2026 · Not medically reviewed. A named clinician has not signed off on this page. How this page is made

Get your N-acetylcysteine today. Order now from Amazon and have it delivered to your door.Shop N-acetylcysteine on AmazonSupport our free guides: as an Amazon Associate we earn from qualifying purchases.

About N-acetylcysteine

N-acetylcysteine (NAC) is a modified form of the amino acid cysteine. It is a long-standing hospital medicine and is also sold as a supplement. The firm facts are about its medicine uses; evidence for supplement uses is small, mixed or low-certainty.

What NAC is

NAC is a modified amino acid. A 2021 review says it was adopted as a mucus-thinning medicine about 60 years ago, is the standard of care for paracetamol (acetaminophen) poisoning, and is on the World Health Organization list of essential medicines. It is also widely described as an antioxidant.

The body uses cysteine and glycine to make glutathione, one of its own antioxidants, and NAC supplies cysteine. A 2021 review says this and other common explanations cannot be generalised to explain most of NAC's effects, and that how it works is still being studied.

^{11 14 10}

Medicine and supplement forms

NAC comes as an intravenous hospital antidote, an inhaled prescription mucus-thinner, and oral capsules, tablets, powders and effervescent forms. MedlinePlus describes the inhaled medicine for thick mucus in lung conditions and notes acetylcysteine is also sometimes used for acetaminophen overdose.

Most trial results on this page are for oral NAC given as a medicine to people with a specific condition. They do not show that NAC pills help healthy people.

^{22 13 2}

NAC and food

No source read gives NAC amounts in foods, so none are stated here. NAC is a supplement and medicine rather than a food nutrient. The body makes cysteine itself, and no trial read compared food sources with NAC pills.

¹⁴

What the research shows

Acetylcysteine is the standard hospital antidote for paracetamol overdose, although the Cochrane review rates the trial evidence low-quality and says practice rests mainly on observational studies. For COPD and chronic bronchitis, pooled mucolytic trials show a small benefit that shrank in newer trials, and a large 2024 NAC trial in milder COPD was null.

For depression, a 2024 meta-analysis found a small add-on effect with wide uncertainty. Evidence is low for PCOS hormones, male semen quality, schizophrenia add-on and flu-like illness. Trials found no benefit in pulmonary fibrosis, kidney protection with contrast dye, or youth cannabis use disorder.

^{2 13 20 12 6 17 5 15 19 16 4}

NAC versus glutathione and other forms

No trial read compared NAC with glutathione, cysteine or glycine pills. The one glutathione trial used a glycine plus NAC mix and missed its main goal. This page gives no amounts to take; if you wonder about your own needs, ask a doctor, pharmacist or dietitian.

¹⁰

At a glance

Traditional uses history, not proof

A hospital antidote for paracetamol (acetaminophen) overdose
A mucus-thinning medicine for lung conditions
Sold as an over-the-counter supplement, often as an 'antioxidant'

Studied for research

Paracetamol overdose antidote, low-quality trial evidence but standard hospital care
Flare-ups in COPD and chronic bronchitis, mixed certainty
Depression added to usual treatment, low certainty
Glutathione levels, very-low certainty
PCOS hormones, male semen quality, schizophrenia add-on and flu-like illness, low certainty
Pulmonary fibrosis, kidney protection from contrast dye and youth cannabis use disorder, evidence against

Main compounds

N-acetylcysteine
Glycine plus NAC (GlyNAC)

Common forms

Oral capsules, tablets, powders and effervescent forms
Inhaled acetylcysteine (prescription mucolytic)
Intravenous acetylcysteine (hospital antidote)

Research links: 2018 Cochrane review: treatments for paracetamol overdose · 2019 Cochrane review: mucolytics for chronic bronchitis and COPD · 2024 meta-analysis: NAC for depression (12 trials) · 2014 trial: acetylcysteine in pulmonary fibrosis · FDA: enforcement discretion for certain NAC products · Research Library · Genes & Biomarkers Library

What it is and its history

Accepted scientific name: N-acetylcysteine (N-acetyl-L-cysteine, NAC)
Synonyms: acetylcysteine; N-acetyl-L-cysteine
Common names: NAC (English); N-acetylcysteine (English); Acetylcysteine (English); N-acetilcisteina (Spanish); Acetilcisteina (Spanish)
Family or group: A modified amino acid and a cysteine prodrug (LiverTox; a 2021 review). Not an essential nutrient.
Look-alikes and adulterants: Name: Cysteine / L-cysteine; Note: The amino acid NAC is made from. NAC is a cysteine derivative; it is a different compound with its own page.; Name: Glutathione; Note: The body's own antioxidant built from cysteine, glycine and glutamate. NAC is studied as a way to supply cysteine for it; it is not glutathione.; Name: GlyNAC; Note: A mix of glycine and NAC studied for glutathione status; results for the mix are not results for NAC alone.
Sustainability and conservation: Not assessed.

Traditional use and history history, not clinical proof

Tradition or era	Documented use	Source
About 1960s, medicine	A 2021 review says NAC was adopted as a mucus-thinning medicine about 60 years ago, and a 2023 review says it was discovered in the early 1960s.	p34171332
Modern hospital medicine	NAC became the standard antidote for paracetamol poisoning and is on the World Health Organization list of essential medicines (2021 review).	p34171332
United States supplement market	The FDA says NAC-containing products labelled as supplements have been sold in the US for over 30 years (statement from April 2022), although it also says NAC was approved as a drug before it was sold as a supplement.	s-fda-nac

Traditional use shows how it was used. It does not show that it works or is safe today.

What is inside, and how it may work

What it contains and how those compounds act in cells and animals. Laboratory and animal mechanisms are not proven effects in people.

Main compounds

Compound	Family	Where it is concentrated	Activity studied	Level of evidence
N-acetylcysteine (NAC)	Cysteine derivative (modified amino acid)	Not read from a source.	Supplies cysteine, a building block of glutathione; used as a mucolytic and as an antidote for paracetamol poisoning. Often described as an antioxidant. ^{11 14 2}	Human data
Glycine plus NAC (GlyNAC)	Amino acid mix	1:1 ratio in the trial read.	Tested for glutathione status in healthy older adults; the main outcome was not met. ¹⁰	Human data

Mechanisms, receptors and pathways

Target or pathway	Gene or receptor	What was found	Level
Cysteine and glutathione supply	Not applicable	NAC is a precursor of cysteine and therefore of glutathione (2023 review). Glutathione is built from glycine and cysteine (2022 trial). A 2021 review says this explanation, and the ideas that NAC scavenges reactive oxygen or breaks disulfide bonds, cannot be generalised to most settings. ^{14 10 11}	Human and lab
Conversion to hydrogen sulfide and sulfane sulfur species	Not applicable	A 2021 review proposes that NAC is converted into hydrogen sulfide and sulfane sulfur species, whose antioxidant and cell-protective activity may explain many effects once credited to NAC or NAC-derived glutathione. This is an emerging idea, mostly from lab work. ¹¹	Lab
Mucus thinning (mucolytic action)	Not applicable	Mucolytics are believed to reduce the stickiness (viscosity) of sputum so it is easier to cough up (Cochrane review). ¹³	Human data

Absorption, metabolism and elimination

Absorption: In a small old study of 12 healthy adults, oral acetylcysteine was absorbed quickly, and a single large dose and repeated smaller doses gave similar peak and total blood levels. The abstract is truncated, so absorption percentages were not read.
Distribution: Not read from a source.
Metabolism: Not read from a source (a 2021 review says NAC may be converted to hydrogen sulfide and sulfane sulfur species).
Elimination: Not read from a source.
Bioavailability: Not given in the abstracts read.

^{3 14 11}

Isolated compounds versus whole extracts

NAC is a single compound sold as a supplement or medicine. No source read gives NAC amounts in foods. Protein foods supply cysteine, which the body also makes itself, but no trial read compared food with NAC pills. Results on this page are for oral NAC, a hospital drug, or a glycine and NAC mix.

Nutritional composition

NAC is not an essential nutrient, and no source read gave NAC amounts in foods. The existing NAC summary says the body can make cysteine itself.

11benefits and uses looked at

22studies and sources checked

Low certaintybest evidence rating found

5lab markers tracked in trials

1 mixed findings6 low certainty1 very low certainty3 evidence against

What was looked at

The 11 benefits and uses checked for N-acetylcysteine, each with how strong the evidence is. Tap one to open it.

Paracetamol (acetaminophen) overdose antidoteLow certainty
Thick mucus and flare-ups in COPD and chronic bronchitisMixed findings
Depression (added to usual treatment)Low certainty
Raising the body's glutathione (with glycine)Very low certainty
Idiopathic pulmonary fibrosisEvidence against
Protecting the kidneys from X-ray contrast dyeEvidence against
Hormones in polycystic ovary syndrome (PCOS)Low certainty
Schizophrenia symptoms (added to usual treatment)Low certainty
Cannabis use disorder in young peopleEvidence against
Sperm quality in men with infertilityLow certainty
Flu-like illness over winterLow certainty

Lab markers tracked in the studies

Reduced-to-oxidised glutathione ratioTotal glutathione in bloodTestosterone and FSH in PCOSSemen quality measuresForced vital capacity (FVC)

What is N-acetylcysteine good for?

The main studied uses and how strong the human evidence is for each. Most results are for NAC as a medicine or in people with a specific condition, not for healthy people taking supplements.

Paracetamol (acetaminophen) overdose antidoteLow certaintyIn hospitals, acetylcysteine is the standard antidote. A 2018 Cochrane review of 11 trials found it appeared better than placebo, but the trials were small and at high risk of bias. This is emergency care given by clinicians, not a supplement use. Thick mucus and flare-ups in COPD and chronic bronchitisMixed findingsA Cochrane review of 38 trials of oral mucolytics (NAC among them) found people were somewhat more likely to be free of flare-ups, but benefit shrank in newer trials. A large 2024 trial of NAC in mild-to-moderate COPD found no significant fall in flare-ups and no change in lung function. Depression (added to usual treatment)Low certaintyA 2024 meta-analysis of 12 trials found a small extra fall in depression scores when NAC was added to usual treatment (SMD -0.24, wide range). Larger trials are needed. It is an add-on, not a replacement for treatment. Raising the body's glutathione (with glycine)Very low certaintyIn 114 healthy older adults, a glycine plus NAC mix for 2 weeks did not raise the main glutathione measures. Only an after-the-fact subgroup showed a rise. The trial was linked to a company that markets such products. Idiopathic pulmonary fibrosisEvidence againstIn a 2014 trial of 264 people, acetylcysteine alone did not slow the loss of lung capacity compared with placebo over 60 weeks. Protecting the kidneys from X-ray contrast dyeEvidence againstIn the 2018 PRESERVE trial of 4,993 high-risk people, 5 days of oral acetylcysteine did not lower death, dialysis or lasting kidney decline at 90 days (4.6% versus 4.5%). Hormones in polycystic ovary syndrome (PCOS)Low certaintyA 2023 meta-analysis of 18 studies found NAC lowered total testosterone and raised FSH, with no clear change in other measures. These are hormone markers; no births were reported in the abstract. Schizophrenia symptoms (added to usual treatment)Low certaintyA 2020 meta-analysis of 7 small trials found better negative and total symptom scores and working memory after 24 weeks or more when NAC was added to usual treatment. The abstract gives no numbers. Cannabis use disorder in young peopleEvidence againstIn a 2025 trial of 192 young people, NAC for 12 weeks did not increase cannabis-free urine tests compared with placebo, and stomach and bowel side effects were more common. Sperm quality in men with infertilityLow certaintyA 2025 meta-analysis of 5 trials found better semen volume, concentration, motility and shape with NAC. These are lab measures; the abstract gives no pregnancy or birth results. Flu-like illness over winterLow certaintyIn a 1997 Italian trial of 262 mostly older people, 6 months of NAC lowered the number and severity of flu-like episodes. It did not prevent infection. One older trial.

Benefits, one by one

Each card is a research question, not a promise. Tap a goal to filter. Open a card to see the studies, doses and limits.

Paracetamol (acetaminophen) overdose antidote

Low certainty

In hospitals, acetylcysteine is the standard antidote for a paracetamol overdose. A 2018 Cochrane review of 11 trials found it appeared better than placebo, but the trials were small and at high risk of bias, so the quality of evidence was low. The authors still conclude it should be given to people at risk of liver damage. This is emergency care given by clinicians. Supplement pills are not a substitute.

2 studiesIntravenous or oral acetylcysteine regimens used in hospital; not a s…

Studies, doses and limits

What the trials found

The 2018 Cochrane review included 11 randomised trials (700 people). Acetylcysteine appeared better than placebo and had fewer adverse effects than dimercaprol or cysteamine. Its edge over methionine was unproven. One small trial in people with fulminant liver failure found fewer deaths with acetylcysteine (Peto OR 0.29, 95% CI 0.09 to 0.94, low-quality evidence). One trial found a 12-hour regimen caused fewer adverse reactions than the older 20.25-hour regimen. The authors say current practice rests mainly on observational studies, which suggest less illness and fewer deaths.

Results

Standard hospital antidote with limited trial evidence. The treatment is given by clinicians, by vein or by mouth. It is not a self-treatment.

Effect sizes as reported

Fulminant liver failure deaths: Peto OR 0.29 (0.09 to 0.94); all trials high risk of bias; quality low or very low.

Why this rating

Low-quality trial evidence per the Cochrane review (small trials, high risk of bias). Its place in hospital care rests mainly on observational studies and expert practice. The evidence is for adults.

Form and dose studied

Intravenous or oral acetylcysteine regimens used in hospital; not a supplement use.

Who was studied

Adults who had taken a paracetamol overdose. Children were not included in most trials.

Limits

All 11 trials were high risk of bias and underpowered. Several different regimens were compared, and it is unclear which is best.

Why researchers looked

Paracetamol is the most widely used non-prescription pain reliever, and overdose is a common cause of sudden liver injury.

Traditional use

NAC is a medicine first. Its roles as a hospital drug are well established; that is different from showing that NAC supplements help healthy people.

Proposed mechanism Established medicine use

Acetylcysteine is thought to help the body neutralise the toxic by-product of paracetamol. The abstracts read describe it as an antidote that detoxifies the toxic metabolite; the exact chemistry was not examined here.

A proposed mechanism does not show that the effect happens in people.

The intravenous form can cause allergy-like reactions (see the Safety tab). Any paracetamol overdose is an emergency even if the person feels well.

^{2 22}

Thick mucus and flare-ups in COPD and chronic bronchitis

Mixed findings

NAC is a mucolytic, a medicine that thins mucus. A 2019 Cochrane review of 38 trials of oral mucolytics (NAC was one of several) found people were somewhat more likely to be free of flare-ups, with benefit shrinking in newer trials. A large 2024 trial of NAC alone in 968 people with mild-to-moderate COPD found no significant fall in flare-ups and no change in lung function.

2 studiesOral NAC (and other oral mucolytics) in trials lasting 2 months to 3 …

Studies, doses and limits

What the trials found

Cochrane 2019: 38 trials, 10,377 people, mucolytics pooled (NAC, carbocysteine, erdosteine, ambroxol). Exacerbation-free during the study: Peto OR 1.73 (1.56 to 1.91, moderate certainty), number needed to treat about 8 over 9 months, but with high variation (I2 62%). Fewer days of disability (0.43 fewer per month). Probably fewer hospital stays (OR 0.68). Little effect on lung function or quality of life. Newer and longer trials showed smaller benefit than early ones. The 2024 trial (Zhou, China): NAC or placebo for 2 years in mild-to-moderate COPD; flare-ups 0.65 versus 0.72 per patient-year, RR 0.90 (0.80 to 1.02, not significant); lung function did not differ.

Results

Mixed. The pooled result favours mucolytics a little, but it is not specific to NAC and has weakened in newer trials. The latest large NAC-only trial in milder COPD was null.

Effect sizes as reported

Cochrane: exacerbation-free OR 1.73 (1.56 to 1.91). 2024 trial: RR 0.90 (0.80 to 1.02).

Why this rating

Cochrane rates its main finding moderate certainty, but benefits shrink in recent trials, and a large 2024 NAC trial did not show a significant effect. Several drugs were pooled in the review.

Form and dose studied

Oral NAC (and other oral mucolytics) in trials lasting 2 months to 3 years.

Who was studied

Adults with chronic bronchitis or COPD (not asthma or cystic fibrosis).

Limits

Pooled drugs are not NAC alone. Early trials may have overstated the benefit. The 2024 trial covered only mild-to-moderate COPD in China.

Why researchers looked

Thick mucus and repeated flare-ups are a major burden in COPD, and NAC has been used to thin mucus for about 60 years.

Traditional use

NAC is a medicine first. Its roles as a hospital drug are well established; that is different from showing that NAC supplements help healthy people.

Proposed mechanism Established medicine use

Mucolytics are believed to thin sputum so it is easier to cough up (Cochrane review). A newer review suggests the usual explanations for NAC's effects are not settled.

A proposed mechanism does not show that the effect happens in people.

The Cochrane review found no clear rise in adverse events with mucolytics. People with lung disease should be guided by their own doctor.

^{13 20}

Depression (added to usual treatment)

Low certainty

A 2024 meta-analysis of 12 trials (904 people) found a small extra fall in depression scores when NAC was added to usual treatment (SMD -0.24). The range of uncertainty is wide, and the authors say larger trials are needed. The benefit looked clearer in bipolar disorder. It was an add-on, not a replacement for treatment.

1 studiesOral NAC as an add-on to medicines or other treatment.

Studies, doses and limits

What the trials found

12 randomised trials, 904 people with depression (bipolar disorder or major depression), NAC added to usual care for 8 to 24 weeks. The change in depression score favoured NAC: standardised mean difference -0.24 (95% CI -0.44 to -0.05; I2 45%). The authors say NAC can ease symptoms, particularly in bipolar disorder, but need larger trials.

Results

Preliminary and small. A statistically significant but small average effect with a wide range.

Effect sizes as reported

SMD -0.24 (95% CI -0.44 to -0.05).

Why this rating

Small effect, wide confidence range, small trials and mixed conditions. Rated low by this page's reading of the meta-analysis; the authors themselves call for larger trials.

Form and dose studied

Oral NAC as an add-on to medicines or other treatment.

Who was studied

People with depression (bipolar or major depressive disorder) already on treatment.

Limits

Small trials; mixed conditions; add-on use only. It does not show NAC works alone.

Why researchers looked

Depression often responds only partly to usual treatments, and NAC has been tried as an add-on.

Traditional use

NAC is a medicine first. Its roles as a hospital drug are well established; that is different from showing that NAC supplements help healthy people.

Proposed mechanism Not established

Not established. The review does not give a mechanism.

A proposed mechanism does not show that the effect happens in people.

Anyone with depression should not stop or change treatment without their doctor. Stomach upset is the most commonly reported effect in NAC trials (see the Safety tab).

¹²

Raising the body's glutathione (with glycine)

Very low certainty

The body uses cysteine and glycine to make glutathione, one of its own antioxidants, and NAC supplies cysteine. In a 2022 trial of 114 healthy older adults, a glycine plus NAC mix for 2 weeks did not raise the main glutathione measures. Only an after-the-fact look at people with high oxidative stress and low glutathione showed a rise. The trial was linked to a company that markets such products.

1 studiesGlycine plus NAC (GlyNAC) as a mix; not NAC alone.

Studies, doses and limits

What the trials found

114 healthy adults (average age 65) took a 1:1 mix of glycine and NAC (three different amounts) or placebo for 2 weeks. The mix was safe and well tolerated. The main outcome was not met: reduced-to-oxidised glutathione ratio 12.49 (placebo) versus 12.65 (top amount), p=0.739; total glutathione 903.5 versus 959.6 mg/L, p=0.278. In a post-hoc subgroup with high oxidative stress and low baseline glutathione, total glutathione was higher at the middle and top amounts (819.7 versus 905.4 mg/L, p=0.016). Older adults also had higher oxidative-stress markers at the start than young adults.

Results

Not shown in healthy older adults overall. A possible effect in a high-stress, low-glutathione subgroup is unconfirmed.

Effect sizes as reported

Ratio 12.49 vs 12.65 (p=0.739); total glutathione 903.5 vs 959.6 mg/L (p=0.278); subgroup 819.7 vs 905.4 mg/L (p=0.016, post hoc).

Why this rating

The main outcome was missed and the only positive finding came from an after-the-fact subgroup analysis in a 2-week trial. It tested glycine plus NAC, not NAC alone, and was linked to a company with a commercial interest.

Form and dose studied

Glycine plus NAC (GlyNAC) as a mix; not NAC alone.

Who was studied

Healthy adults, average age 65.

Limits

Short trial; mix rather than NAC alone; industry-linked; blood levels are not health outcomes.

Why researchers looked

NAC is often sold as a way to support glutathione, so researchers have tested whether pills change glutathione in the blood.

Traditional use

NAC is a medicine first. Its roles as a hospital drug are well established; that is different from showing that NAC supplements help healthy people.

Proposed mechanism Established nutrition

NAC supplies cysteine, which is a building block of glutathione. That is established biology, but a newer review says it does not explain most of NAC's effects.

A proposed mechanism does not show that the effect happens in people.

Described by the authors as safe and well tolerated over 2 weeks.

¹⁰

Idiopathic pulmonary fibrosis

Evidence against

In a 2014 trial of 264 people with idiopathic pulmonary fibrosis, acetylcysteine alone did not slow the loss of lung capacity compared with placebo over 60 weeks (a change of -0.18 L versus -0.19 L). Deaths and sudden worsening did not differ significantly.

1 studiesOral acetylcysteine alone in the two-group stage.

Studies, doses and limits

What the trials found

The IPF Clinical Research Network trial first tested a three-drug mix (prednisone, azathioprine and acetylcysteine), acetylcysteine alone or placebo. The three-drug arm was stopped for safety concerns, and the trial went on with 133 people on acetylcysteine and 131 on placebo. After 60 weeks, forced vital capacity fell by 0.18 L with acetylcysteine and 0.19 L with placebo (P=0.77). Deaths were 4.9% versus 2.5% (P=0.30). Acute worsening was 2.3% in each group.

Results

No benefit shown for lung capacity.

Effect sizes as reported

FVC change -0.18 L vs -0.19 L, P=0.77.

Why this rating

A well-run, government-funded randomised trial found no benefit on its main outcome.

Form and dose studied

Oral acetylcysteine alone in the two-group stage.

Who was studied

Adults with mild-to-moderate idiopathic pulmonary fibrosis.

Limits

One trial; mild-to-moderate disease only.

Why researchers looked

NAC was suggested as a treatment for this scarring lung disease, so a placebo-controlled trial tested it.

Traditional use

NAC is a medicine first. Its roles as a hospital drug are well established; that is different from showing that NAC supplements help healthy people.

Proposed mechanism Not established

Not established.

A proposed mechanism does not show that the effect happens in people.

The earlier three-drug arm (prednisone, azathioprine, acetylcysteine) was stopped for safety concerns; the abstract does not say which drug was responsible.

⁶

Protecting the kidneys from X-ray contrast dye

Evidence against

In the 2018 PRESERVE trial of 4,993 high-risk people having angiography, 5 days of oral acetylcysteine did not lower the chance of death, dialysis or lasting kidney decline at 90 days (4.6% versus 4.5% with placebo). Contrast-related kidney injury did not differ either.

1 studiesOral acetylcysteine for 5 days around angiography.

Studies, doses and limits

What the trials found

5,177 patients at high risk of kidney problems were randomly assigned to oral acetylcysteine or placebo and to bicarbonate or saline. The main outcome (death, dialysis or a lasting rise in creatinine) occurred in 114 of 2,495 on acetylcysteine and 112 of 2,498 on placebo (OR 1.02, 95% CI 0.78 to 1.33, P=0.88). There were no significant differences in contrast-associated kidney injury. The sponsor stopped the trial after a planned interim analysis.

Results

No benefit shown.

Effect sizes as reported

OR 1.02 (0.78 to 1.33).

Why this rating

A large, government-funded randomised trial found no benefit on its main outcome.

Form and dose studied

Oral acetylcysteine for 5 days around angiography.

Who was studied

High-risk adults having angiography.

Limits

Results are for people at high risk having angiography, not the general public.

Why researchers looked

Dye used in angiography can harm the kidneys, and NAC was widely used in the hope of protecting them.

Traditional use

NAC is a medicine first. Its roles as a hospital drug are well established; that is different from showing that NAC supplements help healthy people.

Proposed mechanism Not established

Not established.

A proposed mechanism does not show that the effect happens in people.

No safety signal was singled out in the abstract.

¹⁷

Hormones in polycystic ovary syndrome (PCOS)

Low certainty

A 2023 meta-analysis of 18 studies (2,185 women with PCOS) found NAC lowered total testosterone and raised FSH, but did not clearly change follicle number, womb-lining thickness, progesterone or luteinising hormone. These are hormone measures. The abstract gives no pregnancy or birth results.

1 studiesOral NAC; amounts varied and were not given in the abstract.

Studies, doses and limits

What the trials found

18 studies, 2,185 participants. Total testosterone: SMD -0.25 (95% CI -0.39 to -0.10; I2 53.9%). FSH: SMD 0.39 (0.07 to 0.71; I2 70.9%). Oestrogen rose only after a correction for publication bias. No significant effect on follicle number, endometrial thickness, progesterone, LH or SHBG.

Results

Small changes in some hormones; no clear effect on the others.

Effect sizes as reported

Testosterone SMD -0.25; FSH SMD 0.39.

Why this rating

Hormone markers only, large differences between studies, and no births reported in the abstract.

Form and dose studied

Oral NAC; amounts varied and were not given in the abstract.

Who was studied

Women with PCOS.

Limits

Lab hormone changes are not proof of better ovulation or fertility. The abstract does not report study quality or dose.

Why researchers looked

PCOS is a common hormone condition, and NAC has been tried for its hormone and ovulation effects.

Traditional use

NAC is a medicine first. Its roles as a hospital drug are well established; that is different from showing that NAC supplements help healthy people.

Proposed mechanism Not established

Not established.

A proposed mechanism does not show that the effect happens in people.

The abstract does not report side effects.

¹⁵

Schizophrenia symptoms (added to usual treatment)

Low certainty

A 2020 meta-analysis of 7 trials (440 people) found NAC added to usual treatment improved negative and total symptom scores and working memory after 24 weeks or more. The abstract gives no numbers, and the trials were small. It is an add-on, never a replacement for medicine.

1 studiesOral NAC added to usual treatment.

Studies, doses and limits

What the trials found

7 randomised trials, 220 people on NAC and 220 on placebo. PANSS negative and total scores were significantly better with NAC after 24 weeks, and the thinking skill of working memory improved. Effects appeared only at the later time point.

Results

Possible add-on benefit that needs bigger trials.

Effect sizes as reported

Numbers are not in the abstract.

Why this rating

Few small trials, effects seen only at 24 weeks or later, and no effect sizes in the abstract.

Form and dose studied

Oral NAC added to usual treatment.

Who was studied

People with schizophrenia already on treatment.

Limits

Small trials; add-on use; the abstract does not give effect sizes or amounts.

Why researchers looked

NAC has been tried alongside antipsychotic medicines for symptoms that medicines do not fully relieve.

Traditional use

NAC is a medicine first. Its roles as a hospital drug are well established; that is different from showing that NAC supplements help healthy people.

Proposed mechanism Not established

Not established.

A proposed mechanism does not show that the effect happens in people.

People with schizophrenia should not change their treatment without their doctor.

¹⁹

Cannabis use disorder in young people

Evidence against

In a 2025 trial of 192 young people aged 14 to 21, NAC for 12 weeks did not increase cannabis-free urine tests compared with placebo (RR 0.93), and stomach and bowel side effects were more common with NAC. Earlier positive youth results had come when NAC was paired with a strong behavioural programme.

1 studiesOral NAC, without contingency management.

Studies, doses and limits

What the trials found

192 treatment-seeking young people got NAC or placebo for 12 weeks plus weekly medical management and brief counselling. Negative urine cannabinoid tests: RR 0.93 (95% CI 0.53 to 1.64, P=0.80). Self-reported abstinence: RR 1.02 (0.63 to 1.65). Use days and grams used fell over time in both groups. The authors say an adult trial was not positive.

Results

No benefit shown in this trial.

Effect sizes as reported

RR 0.93 (0.53 to 1.64).

Why this rating

A single double-blind randomised trial found no difference. Earlier positive results were in a different setting.

Form and dose studied

Oral NAC, without contingency management.

Who was studied

Young people aged 14 to 21.

Limits

One trial; some authors report consulting for drug companies.

Why researchers looked

There are few treatments for cannabis use disorder in young people, so NAC has been tested.

Traditional use

NAC is a medicine first. Its roles as a hospital drug are well established; that is different from showing that NAC supplements help healthy people.

Proposed mechanism Not established

Not established.

A proposed mechanism does not show that the effect happens in people.

Stomach and bowel adverse events: 63 of 98 on NAC versus 37 of 94 on placebo.

⁵

Sperm quality in men with infertility

Low certainty

A 2025 meta-analysis of 5 trials found better semen volume, sperm concentration, motility and shape with NAC in men with infertility or poor semen. These are lab measures. The abstract gives no pregnancy or birth results.

1 studiesOral NAC; amounts were not given in the abstract.

Studies, doses and limits

What the trials found

5 randomised trials. Mean differences with NAC versus control: volume 0.69 (0.26 to 1.12), concentration 4.43 (1.50 to 7.36), total motility 9.69 (6.61 to 12.77), normal shape 1.36 (0.70 to 2.03). The authors report no side effects in the included studies.

Results

Better semen measures in a few small trials.

Effect sizes as reported

See the studies table.

Why this rating

Few small trials, lab measures only, and no live births reported in the abstract.

Form and dose studied

Oral NAC; amounts were not given in the abstract.

Who was studied

Men with infertility or impaired semen quality.

Limits

A five-trial analysis; study quality was not summarised in the abstract.

Why researchers looked

Oxidative stress is thought to harm sperm, so antioxidants such as NAC have been tested.

Traditional use

NAC is a medicine first. Its roles as a hospital drug are well established; that is different from showing that NAC supplements help healthy people.

Proposed mechanism Not established

Not established.

A proposed mechanism does not show that the effect happens in people.

No side effects were reported in the included trials.

¹⁶

Flu-like illness over winter

Low certainty

In a 1997 Italian trial of 262 mostly older people, NAC for 6 months over winter lowered the number and severity of flu-like episodes. Among those infected with the H1N1 virus, 25% on NAC had symptoms versus 79% on placebo. It did not prevent infection.

1 studiesOral NAC tablets for 6 months.

Studies, doses and limits

What the trials found

262 people (78% aged 65 or older; people with chronic lung disease excluded) took NAC tablets or placebo for 6 months. NAC reduced the frequency, severity and bed days of flu-like episodes. Infection with the H1N1 virus was equally common in both groups, but 25% of infected people on NAC developed symptoms versus 79% on placebo.

Results

Fewer and milder flu-like episodes in one older trial.

Effect sizes as reported

Symptomatic among infected: 25% vs 79%.

Why this rating

One older trial; not repeated in the sources read.

Form and dose studied

Oral NAC tablets for 6 months.

Who was studied

Mostly adults aged 65 or older, without chronic lung disease.

Limits

Single 1997 trial; funding not stated in the abstract.

Why researchers looked

NAC was tested to see whether it could soften flu-like illness in older people.

Traditional use

NAC is a medicine first. Its roles as a hospital drug are well established; that is different from showing that NAC supplements help healthy people.

Proposed mechanism Not established

Not established.

A proposed mechanism does not show that the effect happens in people.

The abstract says NAC was well tolerated.

⁴

Connections to the rest of health

How N-acetylcysteine connects to the rest of our health knowledge graph. Every link says what kind of connection it is. A safety link (for example to the liver) is a warning, not a benefit. A study that merely mentions a topic never creates a benefit link.

Explore every connection: goals, body systems, organs, symptoms, genes

Kind of connection Connected to Search

A. Wellness goals

Connected to	Evidence status	Context	Studies
Lung Support	Mixed findings	Thick mucus and flare-ups in COPD and chronic bronchitis: NAC is a mucolytic, a medicine that thins mucus. A 2019 Cochrane review of 38 trials of oral mucolytics (NAC was one of several) found people were somewhat more likely to be free of flare-ups, with benefit shrinking in newer trials. A large 2024 trial of NAC alone in 968 people with mild-to-moderate COPD found no significant fall in flare-ups and no change in lung function.	^{13 20}
Mood Balance	Low certainty	Depression (added to usual treatment): A 2024 meta-analysis of 12 trials (904 people) found a small extra fall in depression scores when NAC was added to usual treatment (SMD -0.24). The range of uncertainty is wide, and the authors say larger trials are needed. The benefit looked clearer in bipolar disorder. It was an add-on, not a replacement for treatment.	¹²
Cellular Protection	Very low certainty	Raising the body's glutathione (with glycine): The body uses cysteine and glycine to make glutathione, one of its own antioxidants, and NAC supplies cysteine. In a 2022 trial of 114 healthy older adults, a glycine plus NAC mix for 2 weeks did not raise the main glutathione measures. Only an after-the-fact look at people with high oxidative stress and low glutathione showed a rise. The trial was linked to a company that markets such products.	¹⁰
Lung Support	Evidence against	Idiopathic pulmonary fibrosis: In a 2014 trial of 264 people with idiopathic pulmonary fibrosis, acetylcysteine alone did not slow the loss of lung capacity compared with placebo over 60 weeks (a change of -0.18 L versus -0.19 L). Deaths and sudden worsening did not differ significantly.	⁶
Womens Wellness	Low certainty	Hormones in polycystic ovary syndrome (PCOS): A 2023 meta-analysis of 18 studies (2,185 women with PCOS) found NAC lowered total testosterone and raised FSH, but did not clearly change follicle number, womb-lining thickness, progesterone or luteinising hormone. These are hormone measures. The abstract gives no pregnancy or birth results.	¹⁵
Fertility Support	Low certainty	Hormones in polycystic ovary syndrome (PCOS): A 2023 meta-analysis of 18 studies (2,185 women with PCOS) found NAC lowered total testosterone and raised FSH, but did not clearly change follicle number, womb-lining thickness, progesterone or luteinising hormone. These are hormone measures. The abstract gives no pregnancy or birth results. Sperm quality in men with infertility: A 2025 meta-analysis of 5 trials found better semen volume, sperm concentration, motility and shape with NAC in men with infertility or poor semen. These are lab measures. The abstract gives no pregnancy or birth results.	^{15 16}
Mens Vitality	Low certainty	Sperm quality in men with infertility: A 2025 meta-analysis of 5 trials found better semen volume, sperm concentration, motility and shape with NAC in men with infertility or poor semen. These are lab measures. The abstract gives no pregnancy or birth results.	¹⁶
Immune Support	Low certainty	Flu-like illness over winter: In a 1997 Italian trial of 262 mostly older people, NAC for 6 months over winter lowered the number and severity of flu-like episodes. Among those infected with the H1N1 virus, 25% on NAC had symptoms versus 79% on placebo. It did not prevent infection.	⁴
Seasonal Wellness	Low certainty	Flu-like illness over winter: In a 1997 Italian trial of 262 mostly older people, NAC for 6 months over winter lowered the number and severity of flu-like episodes. Among those infected with the H1N1 virus, 25% on NAC had symptoms versus 79% on placebo. It did not prevent infection.	⁴

B. Body systems

Connected to	Kind of connection	Evidence status	Context	Studies
Liver	Biological association	Low certainty	Studied for: Paracetamol (acetaminophen) overdose antidote	^{2 22}
Hepatic System	Biological association	Low certainty	Studied for: Paracetamol (acetaminophen) overdose antidote	^{2 22}
Respiratory System	Biological association	Mixed findings	Studied for: Thick mucus and flare-ups in COPD and chronic bronchitis Studied for: Idiopathic pulmonary fibrosis	^{13 20 6 4}
Lungs	Biological association	Mixed findings	Studied for: Thick mucus and flare-ups in COPD and chronic bronchitis Studied for: Idiopathic pulmonary fibrosis	^{13 20 6}
Brain	Biological association	Low certainty	Studied for: Depression (added to usual treatment) Studied for: Schizophrenia symptoms (added to usual treatment)	^{12 19 5}
Nervous System	Biological association	Low certainty	Studied for: Depression (added to usual treatment) Studied for: Schizophrenia symptoms (added to usual treatment)	^{12 19 5}
Whole Body	Biological association	Very low certainty	Studied for: Raising the body's glutathione (with glycine)	¹⁰
Kidneys	Biological association	Evidence against	Studied for: Protecting the kidneys from X-ray contrast dye	¹⁷
Urinary System	Biological association	Evidence against	Studied for: Protecting the kidneys from X-ray contrast dye	¹⁷
Endocrine System	Biological association	Low certainty	Studied for: Hormones in polycystic ovary syndrome (PCOS)	¹⁵
Reproductive System	Biological association	Low certainty	Studied for: Hormones in polycystic ovary syndrome (PCOS) Studied for: Sperm quality in men with infertility	^{15 16}
Immune System	Biological association	Low certainty	Studied for: Flu-like illness over winter	⁴

E. Health conditions

Connected to	Evidence status	Context	Studies
Paracetamol (acetaminophen) overdose	Clinical medicine use	Standard hospital antidote; emergency care, not a supplement use. Preparation or compound: Acetylcysteine (hospital antidote)	²
COPD	Mixed findings	Oral mucolytics including NAC gave a small benefit for flare-ups that shrank in newer trials; a 2024 NAC trial was null. Preparation or compound: Oral NAC	^{13 20}
Depression	Preliminary	A small average add-on benefit in a 2024 meta-analysis with a wide range. Preparation or compound: Oral NAC as add-on	¹²

I. Biomarkers

Connected to	Kind of connection	Evidence status	Context	Studies
Reduced-to-oxidised glutathione ratio	Biological association	Very low certainty	Measured in trials: no clear change overall. A lab change is not the same as a health benefit.	¹⁰
Total glutathione in blood	Biological association	Very low certainty	Measured in trials: no clear change overall; higher in a post-hoc subgroup. A lab change is not the same as a health benefit.	¹⁰
Testosterone and FSH in PCOS	Biological association	Low certainty	Measured in trials: testosterone lower, FSH higher. A lab change is not the same as a health benefit.	¹⁵
Semen quality measures	Biological association	Low certainty	Measured in trials: higher. A lab change is not the same as a health benefit.	¹⁶
Forced vital capacity (FVC)	Biological association	Evidence against	Measured in trials: no difference. A lab change is not the same as a health benefit.	⁶

K. Biological pathways

Connected to	Kind of connection	Evidence status	Context	Studies
Glutathione	Preliminary mechanism	Human	Built from cysteine and glycine; NAC is studied as a cysteine source.	^{10 14}
Glycine	Preliminary mechanism	Human	Tested together with NAC in the GlyNAC trial.	¹⁰
Cysteine	Preliminary mechanism	Human	NAC is a derivative and precursor of cysteine.	¹⁴

L. Active compounds

Connected to	Kind of connection	Evidence status	Context	Studies
N-acetylcysteine (NAC)	Biological association	Human	Supplies cysteine, a building block of glutathione; used as a mucolytic and as an antidote for paracetamol poisoning. Often described as an antioxidant.	^{11 14 2}
Glycine plus NAC (GlyNAC)	Biological association	Human	Tested for glutathione status in healthy older adults; the main outcome was not met.	¹⁰

Each connection is stored with the ingredient, the connected record, the kind of connection, the evidence status, the supporting studies, the preparation or compound involved, and a review date (last reviewed October 26, 2026).

Evidence at a glance: what the research found for 11 outcomes

6Low certainty

1Very low certainty

1Mixed findings

3Evidence against

Each outcome below is one thing researchers measured. Certainty is how far the evidence can be trusted, not how well it works. The full studies are on the next tab.

Paracetamol (acetaminophen) overdose antidote 2 studies Low certainty Thick mucus and flare-ups in COPD and chronic bronchitis 2 studies Mixed findings Depression (added to usual treatment) 1 study Low certainty Raising the body's glutathione (with glycine) 1 study Very low certainty Idiopathic pulmonary fibrosis 1 study Evidence against Protecting the kidneys from X-ray contrast dye 1 study Evidence against Hormones in polycystic ovary syndrome (PCOS) 1 study Low certainty Schizophrenia symptoms (added to usual treatment) 1 study Low certainty Cannabis use disorder in young people 1 study Evidence against Sperm quality in men with infertility 1 study Low certainty Flu-like illness over winter 1 study Low certainty

The evidence

The research centre for N-acetylcysteine. Every record here was checked against PubMed or the publisher's page; we never list a study we have not verified.

Evidence by outcome

Bars show how many studies we found for each outcome, not how well it works. People are added up across trials only (reviews are not added, to avoid double counting).

How we rate evidence

High certainty

Several well-run trials or reviews agree; further research is unlikely to change the picture much.

Moderate certainty

Good trials point the same way, but some doubt remains.

Low certainty

Small, short or inconsistent trials. The finding could change with better research.

Very low certainty

Very little or very weak human data. Treat as a possibility only.

Mixed findings

Trials or reviews disagree with each other.

Not enough evidence

Not enough human research to say either way.

Evidence against

Good research found no benefit, or found harm.

We take the reviewers' own risk-of-bias and GRADE statements where they exist, and otherwise judge from study size, design, consistency, directness and whether a product matches what is sold. Many publications do not make evidence high. Method note: We started from our existing NAC summary, read the FDA page and the MedlinePlus drug page in full, and re-read PubMed abstracts for reviews, trials and database entries. Only abstracts were read for studies.

Study library: every study we checked 22

Design Research type Year from Search

Study	Design	People	Product, dose, length	Result
Calverley 2021 Safety of N-Acetylcysteine at High Doses in Chronic Respiratory Diseases: A Review. Drug Saf · PMID 33326056 · DOI	Narrative review	41 articles of NAC used at 600 to 3,000 mg a day in chronic lung diseases (COPD, pulmonary fibrosis, bronchiectasis, chronic bronchitis, cystic fibrosis)	Mostly oral N-acetylcysteine 600 to 3,000 mg a day across the studies reviewed Varied · vs Control groups in trials	The side-effect picture was similar at high and standard amounts with the oral form. Stomach and bowel symptoms were reported but were no more common than in the comparison groups. No numbers in the abstract (Not applicable) Methods, limits and funding Outcomes: Side effects at higher than the standard licensed amount Limitations: Review of studies in people with lung disease, not healthy supplement users. Funding and conflicts: Industry-linked: the analysis was sponsored by pharmaceutical companies, and the authors report consulting and other payments from several drug makers. Read: abstract
Chiew 2018 Interventions for paracetamol (acetaminophen) overdose. Cochrane Database Syst Rev · PMID 29473717 · DOI	Systematic review	700 People who had taken a paracetamol (acetaminophen) overdose; 11 randomised trials of many treatments (mostly adults)	Acetylcysteine given as a hospital antidote (and other overdose treatments) Hospital regimens (intravenous or oral) given by clinicians; not a supplement use Varied by trial · vs Placebo, other antidotes or other regimens	Acetylcysteine appeared better than placebo and caused fewer adverse effects than dimercaprol or cysteamine. One small trial of people with fulminant liver failure found fewer deaths with acetylcysteine. A 12-hour regimen caused fewer adverse reactions than the older 20.25-hour three-bag regimen in one trial. The authors conclude acetylcysteine should be given to people at risk of toxicity, including people with liver failure. They note that current practice rests mainly on observational studies. Fulminant hepatic failure, mortality: Peto OR 0.29 (one small trial, low-quality evidence) (95% CI 0.09 to 0.94) Methods, limits and funding Outcomes: Liver injury, deaths and adverse reactions after paracetamol overdose Limitations: All 11 trials were at high risk of bias and too small to judge efficacy; the quality of evidence was low or very low for all comparisons. Children were not included in most trials. Funding and conflicts: Cochrane authors declare no conflicts (read from record). Read: abstract
De Caro 1989 Pharmacokinetics and bioavailability of oral acetylcysteine in healthy volunteers. Arzneimittelforschung · PMID 2757663	Crossover trial	12 12 healthy adults	Oral acetylcysteine (effervescent tablet and granules) Single 600 mg or repeated 200 mg doses (studied) Single day · vs Two regimens compared with each other	NAC was absorbed quickly, with no significant difference in time to peak between the regimens. A single large dose and repeated small doses gave similar peak and total blood levels. The abstract is truncated, so other details were not read. Not given in the part read (Not given in the part read) Methods, limits and funding Outcomes: Blood levels of NAC over time Limitations: Very small old study; the abstract is cut off. Funding and conflicts: Not stated. Read: abstract
De Flora 1997 Attenuation of influenza-like symptomatology and improvement of cell-mediated immunity with long-term N-acetylcysteine treatment. Eur Respir J · PMID 9230243 · DOI	Randomised controlled trial	262 262 people in 20 Italian centres, 78% aged 65 or older; people with chronic lung disease were excluded	Oral N-acetylcysteine tablets 600 mg twice daily (studied in the trial) 6 months over winter · vs Placebo	Fewer people had influenza-like episodes, and episodes were milder with fewer days in bed. Infection with the H1N1 virus was equally common in both groups, but only 25% of infected people on NAC had symptoms versus 79% on placebo. Symptomatic among virus-infected: 25% vs 79% (Not given in the abstract) Methods, limits and funding Outcomes: Number and severity of influenza-like episodes; days in bed; immune skin-test response Limitations: A single older trial. Funding is not stated in the abstract. It does not show that NAC prevents infection. Funding and conflicts: Funding not stated in the abstract. Read: abstract
Gray 2025 N-acetylcysteine for youth cannabis use disorder: randomized controlled trial main findings. Neuropsychopharmacology · PMID 39910268 · DOI	Randomised controlled trial	192 Young people aged 14 to 21 seeking help for cannabis use disorder	Oral N-acetylcysteine 1,200 mg twice daily (studied in the trial) 12 weeks · vs Placebo; everyone also had weekly medical management and brief counselling	No benefit: negative urine tests and self-reported abstinence did not differ from placebo. Stomach and bowel side effects were more common with NAC (63 of 98 versus 37 of 94). The authors note that earlier positive youth results came when NAC was paired with a strong behavioural programme, and that an adult trial was not positive. Negative urine tests RR 0.93 (95% CI 0.53 to 1.64; P=0.80) Methods, limits and funding Outcomes: Share of urine tests negative for cannabis; self-reported abstinence; side effects Limitations: Young people only. Result applies to NAC without a contingency-management programme. Funding and conflicts: Some authors report consulting for, or research support from, drug companies (read from record). Registration: NCT03055377 Read: abstract
Idiopathic Pulmonary Fibrosis Clinical Research Network; Martinez 2014 Randomized trial of acetylcysteine in idiopathic pulmonary fibrosis. N Engl J Med · PMID 24836309 · DOI	Randomised controlled trial	264 Adults with idiopathic pulmonary fibrosis and mild-to-moderate lung impairment	Oral acetylcysteine alone (two-group stage) 60 weeks · vs Placebo	No benefit: FVC fell by 0.18 L with acetylcysteine and 0.19 L with placebo (P=0.77). Deaths 4.9% versus 2.5% (not significant); acute worsening 2.3% in each group. An earlier three-drug arm (prednisone, azathioprine and acetylcysteine) was stopped for safety concerns. FVC change -0.18 L vs -0.19 L (P=0.77) (Not given in the abstract) Methods, limits and funding Outcomes: Change in forced vital capacity (FVC) over 60 weeks Limitations: Mild-to-moderate disease only. Trial continued as two groups after the three-drug arm was stopped. Funding and conflicts: Funded by the US National Heart, Lung, and Blood Institute and others. Registration: NCT00650091 Read: abstract
Iversen 1992 N-acetylcysteine enhances nitroglycerin-induced headache and cranial arterial responses. Clin Pharmacol Ther · PMID 1505148 · DOI	Randomised controlled trial	11 11 healthy volunteers	N-acetylcysteine (100 mg per kg of body weight, route not stated in the abstract) before an infusion of nitroglycerin 100 mg/kg (studied in the trial; far above supplement amounts) Single session · vs Placebo	NAC made the nitroglycerin headache worse (median score 3 versus 1) and widened a scalp artery more (139% versus 127% of baseline). Headache score 3 vs 1; temporal artery 139% vs 127% (Not given in the abstract) Methods, limits and funding Outcomes: Headache score and width of head and arm arteries Limitations: Very small trial, very high amount, healthy people, a single dose. Not tested with ordinary supplement amounts. Funding and conflicts: No conflicts stated in the record read. Read: abstract
LactMed (NLM) 2006 Acetylcysteine (LactMed, NCBI Bookshelf record) Drugs and Lactation Database (LactMed) · PMID 29999990	Reference database n/a	Drug-and-breastfeeding entry for acetylcysteine	Acetylcysteine as a medicine	LactMed says no information is available on acetylcysteine use during breastfeeding (the record does not say which form this refers to). To avoid infant exposure, nursing mothers may consider pumping and discarding milk for 30 hours after administration. It says inhaled acetylcysteine is very minimally absorbed, so breastfeeding can continue with no special precautions. Not applicable (Not applicable) Methods, limits and funding Outcomes: Use during breastfeeding Limitations: Only the PubMed record of the entry was read, not the full Bookshelf page. The record's date is the original 2006 entry, not the latest revision. Funding and conflicts: Government resource (NLM). Read: abstract
LiverTox (NIDDK) 2012 Acetylcysteine (LiverTox, NCBI Bookshelf record) LiverTox: Clinical and Research Information on Drug-Induced Liver Injury · PMID 31643720	Reference database n/a	Drug-safety entry for acetylcysteine	Acetylcysteine as a medicine	LiverTox calls acetylcysteine a modified amino acid used as an antidote for paracetamol overdose, and a liver-protecting agent. It says acetylcysteine has not been linked to significant liver-enzyme rises during treatment or to clinically apparent acute liver injury. Not applicable (Not applicable) Methods, limits and funding Outcomes: Liver safety Limitations: Only the PubMed record of the entry was read, not the full Bookshelf page. Funding and conflicts: Government resource (NIDDK / NLM). Read: abstract
Lizzo 2022 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 · PMID 35821844 · DOI	Randomised controlled trial	114 Healthy adults, average age 65, compared with a young reference group (n=20)	Glycine plus N-acetylcysteine (GlyNAC) in a 1:1 mix; not NAC alone 2.4, 4.8 or 7.2 g a day of the mix (studied in the trial) 2 weeks · vs Placebo	The supplement was safe and well tolerated but did not raise the main glutathione measures: ratio 12.49 with placebo versus 12.65 at the top amount (p=0.739); total glutathione 903.5 versus 959.6 mg/L (p=0.278). A later (post-hoc) look at people with high oxidative stress and low glutathione found a rise at the middle and top amounts (819.7 versus 905.4 mg/L, p=0.016). Main outcome not met; post-hoc subgroup difference only (Not given in the abstract) Methods, limits and funding Outcomes: Total glutathione and the ratio of reduced to oxidised glutathione (main outcome) Limitations: Short (2 weeks). The only positive result came from an after-the-fact subgroup analysis. A glycine plus NAC mix, so the effect of NAC alone is unknown. Funding and conflicts: Industry-linked: authors are employees of Nestle Health Science and Nestle Research, whose parent company holds patents and markets glycine and NAC products; a research institute received funding from Nestle Health Science. Registration: NCT05041179 Read: abstract
Pedre 2021 The mechanism of action of N-acetylcysteine (NAC): The emerging role of H(2)S and sulfane sulfur species. Pharmacol Ther · PMID 34171332 · DOI	Narrative review mixed	Review of how NAC works (lab, animal and human work)	N-acetylcysteine	NAC began as a mucolytic about 60 years ago and is the standard of care for paracetamol poisoning and on the WHO essential medicines list. It is often used as an 'antioxidant', usually on the assumption that it scavenges reactive oxygen, breaks disulfide bonds or supplies cysteine for glutathione. The review says these ideas cannot be generalised to most settings and that a newer idea, conversion of NAC into hydrogen sulfide and sulfane sulfur species, may explain many effects. Not applicable (Not applicable) Methods, limits and funding Outcomes: Proposed mechanisms of action Limitations: A review of mechanisms; mostly lab and animal work. The newer idea is not yet settled. Funding and conflicts: Authors declare no conflicts (read from record). Read: abstract
Peng 2024 Efficacy of N-acetylcysteine for patients with depression: An updated systematic review and meta-analysis. Gen Hosp Psychiatry · PMID 39504621 · DOI	Meta-analysis	904 People with depression (bipolar disorder or major depression); 12 randomised trials	Oral N-acetylcysteine added to usual treatment 1,000 to 3,000 mg a day across trials (studied) 8 to 24 weeks · vs Placebo	Depression scores fell a little more with NAC than with placebo. The authors say the benefit was clearer in bipolar disorder and that larger trials are needed because the confidence range is wide. Standardised mean difference -0.24 (small effect); I2 45% (95% CI -0.44 to -0.05; P=.02) Methods, limits and funding Outcomes: Change in depression score from the start to the end of treatment Limitations: Wide confidence range, small trials, mixed conditions. NAC was an add-on, not a stand-alone treatment. Funding and conflicts: Authors declare no conflicts (read from record). Read: abstract
Poole 2019 Mucolytic agents versus placebo for chronic bronchitis or chronic obstructive pulmonary disease. Cochrane Database Syst Rev · PMID 31107966 · DOI	Systematic review	10377 Adults with chronic bronchitis or COPD (not asthma or cystic fibrosis); 38 trials lasting 2 months to 3 years	Oral mucolytics: N-acetylcysteine, carbocysteine, erdosteine, ambroxol (pooled, not NAC alone) Given at least once a day (see trials) 2 months to 3 years · vs Placebo	People on mucolytics were more likely to be free of flare-ups, and had fewer days of disability and probably fewer hospital stays. More recent and longer trials showed smaller benefits than earlier, shorter ones. Little effect on lung function or quality of life. Deaths: too imprecise to tell. Adverse events were not increased. Exacerbation-free: Peto OR 1.73 (28 trials, 6,723 people; moderate certainty; I2 62%). Number needed to treat about 8 over 9 months. Days of disability: 0.43 fewer per month. Hospital stays: OR 0.68 (4 trials). Quality of life: MD -1.37, below the clinically important difference. Deaths: OR 0.98. (Exacerbation-free OR 1.73 (95% CI 1.56 to 1.91); NNT 8 (7 to 10); disability -0.43 days/month (-0.56 to -0.30); hospital stays OR 0.68 (0.52 to 0.89); quality of life MD -1.37 (-2.85 to 0.11); deaths OR 0.98 (0.51 to 1.87)) Methods, limits and funding Outcomes: Flare-ups (exacerbations), days of disability, hospital stays, lung function, quality of life, adverse events Limitations: Several mucolytics pooled, so the result is not specific to NAC. Many trials had unclear blinding and high drop-out. The authors say early trials may have overstated benefit. Funding and conflicts: Cochrane authors declare no conflicts relevant to this work (read from record). Read: abstract
Sahasrabudhe 2023 N-acetylcysteine Pharmacology and Applications in Rare Diseases-Repurposing an Old Antioxidant. Antioxidants (Basel) · PMID 37507857 · DOI	Narrative review mixed	Review of NAC pharmacology and use in rare mitochondrial diseases	N-acetylcysteine	NAC is a precursor of cysteine and so of glutathione. The authors say it was discovered in the early 1960s, has a long history as a prescription product and is also used off-label as an over-the-counter product. They also say systematic studies of how NAC moves through the body, its drug interactions and dose-ranging are sorely limited. Not applicable (Not applicable) Methods, limits and funding Outcomes: History, mechanisms, safety and pharmacokinetics of NAC Limitations: A narrative review; the abstract gives no data. Funding and conflicts: One author reports investigator-initiated funds from Pfizer, Sanofi and the NIH. Read: abstract
Shahveghar Asl 2023 The effects of N-acetylcysteine on ovulation and sex hormones profile in women with polycystic ovary syndrome: a systematic review and meta-analysis. Br J Nutr · PMID 36597797 · DOI	Meta-analysis	2185 Women with polycystic ovary syndrome (PCOS); 18 studies	Oral N-acetylcysteine Varied (not given in the abstract) Varied · vs Placebo or comparison treatment	NAC lowered total testosterone and raised FSH. It did not clearly change follicle number, womb-lining thickness, progesterone, luteinising hormone or sex hormone-binding globulin. Oestrogen rose only after a correction for publication bias. The abstract does not report pregnancy or birth outcomes. Total testosterone SMD -0.25; FSH SMD 0.39 (Testosterone 95% CI -0.39 to -0.10 (I2 53.9%); FSH 0.07 to 0.71 (I2 70.9%)) Methods, limits and funding Outcomes: Hormone levels, number of follicles, endometrial thickness Limitations: Hormone measures, not births. Large differences between studies for FSH. Study quality not summarised in the abstract. Funding and conflicts: No conflicts stated in the record read. Read: abstract
Syarif 2025 Unlocking the potential of antioxidant supplementation with n-acetylcysteine to improve seminal parameters and analysis of its safety: a systematic review and meta-analysis of randomized controlled trials. Arch Ital Urol Androl · PMID 40126496 · DOI	Meta-analysis	Men with infertility or poor semen quality; 5 randomised trials	Oral N-acetylcysteine Not given in the abstract Varied · vs Control	Semen measures were better with NAC. The authors report no side effects in the included studies. The abstract gives no pregnancy or live-birth results. Volume MD 0.69; concentration MD 4.43; total motility MD 9.69; normal shape MD 1.36 (Volume 0.26 to 1.12; concentration 1.50 to 7.36; motility 6.61 to 12.77; shape 0.70 to 2.03) Methods, limits and funding Outcomes: Semen volume, sperm concentration, motility and shape Limitations: Only five trials; lab semen measures rather than fatherhood or births. Funding and conflicts: No conflicts stated in the record read. Read: abstract
Weisbord 2018 Outcomes after Angiography with Sodium Bicarbonate and Acetylcysteine. N Engl J Med · PMID 29130810 · DOI	Randomised controlled trial	4993 5,177 adults at high risk of kidney problems scheduled for angiography (4,993 in the main analysis)	Oral acetylcysteine (and, in a second comparison, intravenous sodium bicarbonate) 5 days of oral acetylcysteine (studied in the trial) 5 days of treatment; 90-day follow-up · vs Oral placebo	No benefit: the main outcome occurred in 4.6% with acetylcysteine and 4.5% with placebo. Kidney injury from contrast dye did not differ either. The sponsor stopped the trial after a planned interim look. Main outcome OR 1.02 (95% CI 0.78 to 1.33; P=0.88) Methods, limits and funding Outcomes: Death, need for dialysis or a lasting rise in blood creatinine at 90 days; contrast-associated kidney injury Limitations: High-risk patients having angiography; not about healthy people. Funding and conflicts: Funded by the US Department of Veterans Affairs and Australia's NHMRC. Registration: NCT01467466 Read: abstract
Yarema 2018 Anaphylactoid Reactions to Intravenous N-Acetylcysteine during Treatment for Acetaminophen Poisoning. J Med Toxicol · PMID 29423816 · DOI	Cohort study	6455 People treated for paracetamol (acetaminophen) overdose in 34 Canadian hospitals, 1980 to 2005 (retrospective record review)	Intravenous N-acetylcysteine, 21-hour hospital protocol Hospital protocol (not a supplement use) 21 hours	Reactions were recorded in 528 of 6,455 treatment courses (8.2%). Three in four were skin reactions (hives, itching, swelling). More than 95% began in the first 5 hours. The authors call these reactions uncommon, mostly skin-only, and say none of the risk factors found were strong enough to change when treatment is started. 8.2% of treatment courses (Female sex adjusted OR 1.24 (1.08 to 1.42) for more severe reactions) Methods, limits and funding Outcomes: Allergy-like (anaphylactoid) reactions during treatment Limitations: Retrospective record review. This is the drug given into a vein in hospital, not oral supplements. Funding and conflicts: Authors declare no conflicts (read from record). Read: abstract
Yolland 2020 Meta-analysis of randomised controlled trials with N-acetylcysteine in the treatment of schizophrenia. Aust N Z J Psychiatry · PMID 31826654 · DOI	Meta-analysis	440 People with schizophrenia taking standard treatment; 7 trials (220 on NAC, 220 on placebo)	Oral N-acetylcysteine added to usual treatment Not given in the abstract Benefits seen at 24 weeks or longer · vs Placebo	Negative-symptom and total PANSS scores were better with NAC after 24 weeks, and working memory improved. Effects were seen only at the later time point. Numbers not given in the abstract (Not given in the abstract) Methods, limits and funding Outcomes: Psychosis symptom scores (PANSS) and thinking skills Limitations: Small trials. The abstract gives no effect sizes. NAC was an add-on to usual care. Funding and conflicts: No conflicts stated in the record read. Read: abstract
Zhou 2024 Effect of high-dose N-acetylcysteine on exacerbations and lung function in patients with mild-to-moderate COPD: a double-blind, parallel group, multicentre randomised clinical trial. Nat Commun · PMID 39349461 · DOI	Randomised controlled trial	968 Adults aged 40 to 80 with mild-to-moderate COPD in China	Oral N-acetylcysteine 600 mg twice daily (studied in the trial) 2 years · vs Matched placebo	Flare-ups were 0.65 per patient-year with NAC and 0.72 with placebo; the difference was not statistically significant. Lung function did not differ at 24 months. Annual exacerbation rate RR 0.90 (95% CI 0.80 to 1.02; P=0.10) Methods, limits and funding Outcomes: Yearly rate of flare-ups; change in lung function (FEV1) Limitations: People with mild-to-moderate COPD only. Done in China; may not apply elsewhere. Funding and conflicts: Authors declare no outside support or conflicts (read from record). Registration: ChiCTR-IIR-17012604 Read: abstract
s-fda-nac FDA: Releases Final Guidance on Enforcement Discretion for Certain NAC Products (constituent update; latest entry 2023-11-29) · Source	Regulator statement n/a			Methods, limits and funding Read: full-text
s-medlineplus-acetylcysteine MedlinePlus Drug Information: Acetylcysteine Oral Inhalation (last revised 2017-03-15) · Source	Reference database n/a			Methods, limits and funding Read: full-text

What we do not know yet

No trial was read showing that NAC pills help healthy, well-fed adults.
The trial evidence for the hospital antidote is low-quality; practice rests mainly on observational studies.
No source on the purity or label accuracy of NAC supplements was read.
Pregnancy safety for oral NAC supplements was not found in the sources read.
NIH Office of Dietary Supplements, NCCIH and European or UK regulator pages on NAC were not read.
NAC for OCD, Parkinson's disease, sleep, heart disease and other uses was not researched here.

How new research is added

New studies are found by a saved PubMed search and placed in a review queue before the page changes.

Lab markers

What changed in blood or saliva tests during trials. A changed number is not the same as feeling or being healthier, and we give no "normal ranges".

Other 5

●

Reduced-to-oxidised glutathione ratio

No clear change overall in trials

Glutathione is a small protein-building molecule the body uses as an antioxidant. The ratio of its reduced form to its oxidised form is used as a sign of oxidative stress.

Very low certainty

Results and what it means

Why it was measured

To see whether glycine plus NAC improves the body's antioxidant balance.

Statistical vs. clinical meaning

No overall change. Marker only; not proof of any health benefit.

Safety implication

None specific beyond those on the Safety tab.

Study	Result	People	Product
¹⁰	12.49 with placebo versus 12.65 at the top amount (p=0.739)	114 healthy adults, average age 65	Glycine plus NAC mix for 2 weeks

¹⁰

●

Total glutathione in blood

No clear change overall; higher in a post-hoc subgroup in trials

The total amount of glutathione (reduced plus oxidised) measured in blood.

Very low certainty

Results and what it means

Why it was measured

To see whether the supplement raises glutathione supply.

Statistical vs. clinical meaning

The pre-planned comparison was negative; the subgroup finding was unplanned.

Safety implication

None specific.

Study	Result	People	Product
¹⁰	903.5 mg/L with placebo versus 959.6 mg/L at the top amount (p=0.278); post-hoc subgroup 819.7 versus 905.4 mg/L (p=0.016)	114 healthy adults; subgroup with high oxidative stress and low glutathione	Glycine plus NAC mix for 2 weeks

¹⁰

●

Testosterone and FSH in PCOS

Testosterone lower, FSH higher in trials

Total testosterone is a male-type hormone that is often raised in PCOS. FSH is a pituitary hormone that helps eggs mature.

Low certainty

Results and what it means

Why it was measured

To see whether NAC shifts hormone levels in PCOS.

Statistical vs. clinical meaning

Hormone markers only; no births reported.

Safety implication

None specific.

Study	Result	People	Product
¹⁵	Total testosterone SMD -0.25 (95% CI -0.39 to -0.10); FSH SMD 0.39 (0.07 to 0.71)	18 studies, 2,185 women with PCOS	Oral NAC; amounts varied

¹⁵

●

Semen quality measures

Higher in trials

Semen volume, sperm concentration, motility (movement) and shape (morphology) measured in a lab.

Low certainty

Results and what it means

Why it was measured

To see whether NAC improves sperm measures in infertile men.

Statistical vs. clinical meaning

Lab measures; no live births in the abstract.

Safety implication

None specific.

Study	Result	People	Product
¹⁶	Total motility MD 9.69 (6.61 to 12.77); concentration MD 4.43 (1.50 to 7.36); volume MD 0.69; normal shape MD 1.36	5 randomised trials in men with infertility or poor semen	Oral NAC; amounts not given in the abstract

¹⁶

●

Forced vital capacity (FVC)

No difference in trials

The most air a person can blow out after taking the deepest breath; used to track lung scarring.

Evidence against

Results and what it means

Why it was measured

To see whether acetylcysteine slows lung decline in pulmonary fibrosis.

Statistical vs. clinical meaning

No difference from placebo.

Safety implication

None specific.

Study	Result	People	Product
⁶	Change -0.18 L with acetylcysteine versus -0.19 L with placebo (P=0.77)	264 people with idiopathic pulmonary fibrosis	Oral acetylcysteine alone for 60 weeks

⁶

Safety

What studies and official sources say about side effects, medicines and who should check first. Each point shows what kind of evidence it comes from.

Main points to know 4

A paracetamol overdose is an emergency; NAC pills are not a substitute. Hospitals give acetylcysteine as an antidote after a paracetamol (acetaminophen) overdose, and the Cochrane review concludes it should be given to people at risk of liver damage. That is emergency care by clinicians, by vein or by mouth. A person can feel well for hours after an overdose and still be at risk. Do not try to treat an overdose at home with supplements. Systematic review and authoritative guidance ^{2 22}
Given into a vein, NAC can cause allergy-like reactions. In a review of 6,455 hospital treatment courses for paracetamol overdose in Canada, 8.2% had an allergy-like (anaphylactoid) reaction to intravenous NAC. Three in four were skin reactions such as hives, itching or swelling, and more than 95% began in the first 5 hours. The authors call them uncommon and mostly skin-only. This is the hospital form given into a vein, not oral supplements. Retrospective cohort ¹⁸
NAC can make nitroglycerin headaches worse. In a very small trial of 11 healthy volunteers, NAC given before nitroglycerin made the headache worse (median score 3 versus 1) and widened a scalp artery more. The NAC amount used was very high and the route was not stated in the abstract. If you take nitroglycerin for heart pain, ask your doctor or pharmacist before adding NAC. Small randomised trial ⁷
Stomach and bowel upset is the most reported effect. Stomach and bowel symptoms are the most commonly reported effects in NAC trials. In a review of 41 articles on lung disease at amounts above the standard licensed one, such symptoms were reported but were no more common than in comparison groups. In a 2025 trial in young people, they were more common with NAC than placebo (63 of 98 versus 37 of 94). Review and randomised trial ^{1 5}

Side effects 4

Effect	How often	Severity and recovery	Evidence
Nausea, vomiting, stomach and bowel upset MedlinePlus separately lists nausea and vomiting for the inhaled medicine.	Youth cannabis trial: stomach and bowel adverse events in 63 of 98 on NAC versus 37 of 94 on placebo. High-amount review in lung disease: no more common than with comparison treatment.	Not rated in the abstracts; the trial reported other adverse events as similar between groups. Not reported in the sources read.	Randomised trial and review ^{5 1}
Allergy-like reactions to intravenous NAC (hives, itching, swelling, low blood pressure, breathing symptoms) Hospital use only. Being female and having taken a single acute overdose were each linked to more severe reactions.	8.2% of 6,455 hospital treatment courses; 75.4% of reactions were skin-only; 95.4% began in the first 5 hours.	Mostly skin-only; some more severe. Most people in the study received an antihistamine (92% of those treated).	Retrospective cohort ¹⁸
Throat irritation, runny nose, drowsiness, fever, mouth swelling (inhaled medicine) This is the prescription inhaled form, not a supplement.	Not given.	MedlinePlus: tell the doctor if severe or persistent. Not stated.	Authoritative guidance ²²
Chest tightness, wheezing, trouble breathing or swallowing, coughing blood, hives, rash (serious, inhaled medicine) MedlinePlus asks people with asthma to tell their doctor before using the inhaled medicine.	Not given.	MedlinePlus: call a doctor immediately or get emergency treatment. Not stated.	Authoritative guidance ²²

Liver

LiverTox says acetylcysteine is a liver-protecting agent used as an antidote for paracetamol overdose and has not been linked to significant liver-enzyme rises during treatment or to clinically apparent acute liver injury. ⁹

How often. No frequency was given in the record read.

Monitoring. No agency monitoring advice was found.

This is a safety connection. It is not evidence that N-acetylcysteine supports liver health.

Medicines and supplements 2

With	Why it matters	Importance	Evidence	What to do
Nitroglycerin (and similar nitrate heart medicines) prescription	The trial abstract describes NAC as a sulfhydryl group donor; in the trial it added to nitroglycerin's blood-vessel widening.	In 11 healthy volunteers, NAC made the nitroglycerin headache worse and widened a scalp artery more. Other nitrate medicines were not tested in the abstract read.	Small randomised trial Low certainty ⁷	Ask a doctor or pharmacist before combining NAC with nitroglycerin.
Other medicines, vitamins and herbal products prescription	Not described in the sources read.	MedlinePlus asks people to tell their doctor and pharmacist about all prescription and non-prescription medicines, vitamins, supplements and herbal products they take. A 2023 review says systematic studies of NAC's drug interactions are sorely limited.	Authoritative guidance and review Low certainty ^{22 14}	Ask a pharmacist to check your own list.

Who should check first 5

Situation	Advice	Evidence
Allergy to acetylcysteine or any ingredient in a product	MedlinePlus (inhaled medicine) asks people allergic to acetylcysteine or any ingredient to tell their doctor and pharmacist. Ask a pharmacist to read the ingredient list of any NAC product.	Authoritative guidance ²²
Asthma	MedlinePlus asks people with asthma to tell their doctor before using the inhaled medicine, and lists wheezing and chest tightness as serious effects. No source read addressed asthma and oral supplements.	Authoritative guidance ²²
Pregnancy	MedlinePlus asks people who are pregnant or planning pregnancy to tell their doctor about the inhaled medicine. No source read gave pregnancy safety data for oral supplements. Ask a doctor or pharmacist.	Authoritative guidance ²²
Breastfeeding	LactMed says no information is available on acetylcysteine during breastfeeding, and that nursing mothers may consider pumping and discarding milk for 30 hours after administration to avoid infant exposure. It says inhaled acetylcysteine is very minimally absorbed, so breastfeeding can continue. The record does not say which form the first statement refers to.	Authoritative guidance ⁸
Children and teenagers	The Cochrane paracetamol review says children were not included in most trials. In a 2025 trial in ages 14 to 21, stomach and bowel side effects were more common with NAC. No source read gave advice on NAC supplements for children. Ask a doctor or pharmacist.	Systematic review and randomised trial ^{2 5}

Overdose, product quality and regulators

Summary. NAC is used as a medicine and is generally reported as well tolerated in trials, but long-term safety in healthy people taking supplements is not well documented in the sources read.

Animal. Not reviewed.

Human doses studied. Amounts used in trials appear only in the studies tables. They are not advice.

High dose or long term signals. A review of higher-than-standard amounts in chronic lung disease found a safety profile similar to the standard amount, with stomach and bowel symptoms no more common than in control groups. That analysis was sponsored by pharmaceutical companies.

Overdose response. No source read described a poisoning from oral NAC supplements. MedlinePlus gives the US poison control number for overdose of the inhaled medicine; call poison control or emergency services if someone has taken a large amount.

Genotoxicity. Not researched.

Contamination and label accuracy of NAC supplements were not researched for this page.

Legal status of NAC supplements in the United States. The FDA says it considers NAC excluded from the definition of a dietary supplement, because NAC was approved as a drug before it was sold as a supplement. In 2022 it issued guidance saying it intends to use enforcement discretion for certain NAC products labelled as supplements. In 2023 it added its safety literature review to its peer review agenda; its earlier review had not revealed safety concerns. This is a regulatory fact, not a quality check of any product. ²¹

Body	Action	Date
US Food and Drug Administration (FDA) (United States)	Says NAC is excluded from the dietary supplement definition because it was approved as a drug first. Final guidance (2022-08-01) says it intends to exercise enforcement discretion for certain NAC products labelled as supplements that would otherwise be lawful. On 2023-11-29 it added its systematic review of NAC literature to its peer review agenda after completing its review of safety information. The April 2022 update stated its initial review had not revealed safety concerns. source	2023-11-29
MedlinePlus Drug Information (ASHP, US National Library of Medicine) (United States)	Describes inhaled acetylcysteine as a prescription mucolytic for thick mucus in lung conditions, lists possible and serious side effects, asks people with asthma, pregnant or breastfeeding people and those on other medicines to tell their doctor, and mentions use for acetaminophen overdose. It does not cover oral supplements. source	2017-03-15
NIH LactMed (drugs and lactation database) (United States)	No information on acetylcysteine use during breastfeeding; pumping and discarding milk for 30 hours after administration may be considered to avoid infant exposure; inhaled acetylcysteine is very minimally absorbed so breastfeeding can continue. source	2006
NIH LiverTox (United States)	Not linked to significant liver-enzyme rises during therapy or to clinically apparent acute liver injury; used as an antidote for paracetamol overdose. source	2012

When to get medical help

Someone has taken more paracetamol (acetaminophen) than directed, even if they feel fine: call poison control or emergency services now.
Hives, swelling of the face, lips or throat, wheezing, chest tightness or trouble breathing or swallowing after using NAC: stop and get emergency medical help.
Coughing up blood, or breathing that gets worse after using an acetylcysteine product: get medical help straight away.
Low mood that worsens, or thoughts of self-harm, in someone with depression: contact a doctor or crisis line; do not rely on supplements.

Stop using the product and contact a clinician or emergency service. In the US, Poison Control is 1-800-222-1222.

General information only, not medical advice. Ask a clinician or pharmacist before use, especially with medicines, in pregnancy or with a health condition. See the Natural Remedy Safety guide.

Frequently asked questions

What is N-acetylcysteine (NAC)?

NAC is a modified form of the amino acid cysteine. It is a hospital medicine and is also sold as a supplement. A 2021 review calls it the standard of care for paracetamol poisoning and says it has been used to thin mucus for about 60 years.

¹¹

Is NAC a supplement or a medicine?

Both. In the US, the FDA says NAC is excluded from the dietary supplement definition because it was approved as a drug first, but it has said it intends to use enforcement discretion for certain products. Rules differ by country.

²¹

Does NAC treat a paracetamol overdose?

In hospitals acetylcysteine is the standard antidote, and the Cochrane review says it should be given to people at risk of liver damage. The trial evidence is low-quality. An overdose is an emergency: call poison control or emergency services. Pills at home are not a substitute.

^{2 22}

Does NAC help COPD or chronic bronchitis?

A Cochrane review of oral mucolytics, NAC among them, found a small benefit for flare-ups that was smaller in newer trials. A 2024 trial of NAC in mild-to-moderate COPD found no significant benefit.

^{13 20}

Does NAC help depression?

A 2024 meta-analysis of 12 trials found a small extra improvement when NAC was added to usual treatment, with a wide range of uncertainty. It is not a replacement for treatment.

¹²

Does NAC raise glutathione?

In a 2022 trial of 114 healthy older adults, a glycine plus NAC mix did not raise the main glutathione measures. Only an after-the-fact subgroup showed a rise. The trial was linked to a company that sells such products.

¹⁰

Does NAC help pulmonary fibrosis or protect the kidneys from contrast dye?

No. A 2014 trial found no benefit in idiopathic pulmonary fibrosis, and the 2018 PRESERVE trial found no benefit for kidney protection around angiography.

^{6 17}

Does NAC help fertility or PCOS?

A 2023 meta-analysis found lower testosterone and higher FSH in PCOS, and a 2025 analysis found better semen measures. These are lab markers; the abstracts give no pregnancy or birth results.

^{15 16}

What are the side effects of NAC?

Stomach and bowel upset is the most reported. Given into a vein in hospital, allergy-like reactions occurred in 8.2% of treatment courses in one review. The inhaled medicine can cause throat irritation and, rarely, wheezing. Seek help for hives, swelling or trouble breathing.

^{5 18 22}

Does NAC interact with medicines?

In a small trial, NAC made the headache from nitroglycerin worse. Other interactions were not found in the sources read, which does not mean there are none. Ask a pharmacist to check your medicines.

^{7 14}

Is NAC safe in pregnancy, breastfeeding and for children?

No source read gave safety data for oral NAC supplements in pregnancy. LactMed says no information is available on use while breastfeeding. Children were not included in most overdose trials. Ask a doctor or pharmacist.

^{8 22 2}

Can NAC harm the liver?

LiverTox says acetylcysteine has not been linked to significant liver-enzyme rises or clinically apparent liver injury. It is used to protect the liver after paracetamol overdose.

⁹

Explore by health goal

Lung Support Fertility Support Mood Balance Cellular Protection Womens Wellness Mens Vitality Immune Support Seasonal Wellness

Editorial transparency

Written by: AlternativeMed editorial team. Research compiled with AI assistance, then checked against the sources listed.
Medical review: None. This page has not been reviewed by a physician or pharmacist.
First published: 2026-10-26
Last substantive update: 2026-10-26
How we research: We started from our existing NAC summary, read the FDA page and the MedlinePlus drug page in full, and re-read PubMed abstracts for reviews, trials and database entries. Only abstracts were read for studies.
How we rate evidence: See "How we rate evidence" in the Evidence tab.
Independence: No product is promoted on this page. No affiliate links are shown. Some trials may have company links not stated in abstracts; those we saw are flagged.

Sources 22

Each source was opened and checked. Where we read only the abstract, it says so. The small numbers in the text point here.

Calverley P, Rogliani P, Papi A. Safety of N-Acetylcysteine at High Doses in Chronic Respiratory Diseases: A Review.. Drug Saf. 2021. PMID 33326056. DOI 10.1007/s40264-020-01026-y. (abstract)
Chiew AL, Gluud C, Brok J, et al.. Interventions for paracetamol (acetaminophen) overdose.. Cochrane Database Syst Rev. 2018. PMID 29473717. DOI 10.1002/14651858.CD003328.pub3. (abstract)
De Caro L, Ghizzi A, Costa R, et al.. Pharmacokinetics and bioavailability of oral acetylcysteine in healthy volunteers.. Arzneimittelforschung. 1989. PMID 2757663. (abstract)
De Flora S, Grassi C, Carati L. Attenuation of influenza-like symptomatology and improvement of cell-mediated immunity with long-term N-acetylcysteine treatment.. Eur Respir J. 1997. PMID 9230243. DOI 10.1183/09031936.97.10071535. (abstract)
Gray KM, Tomko RL, Baker NL, et al.. N-acetylcysteine for youth cannabis use disorder: randomized controlled trial main findings.. Neuropsychopharmacology. 2025. PMID 39910268. DOI 10.1038/s41386-025-02061-y. (abstract)
Idiopathic Pulmonary Fibrosis Clinical Research Network; Martinez FJ, de Andrade JA, et al.. Randomized trial of acetylcysteine in idiopathic pulmonary fibrosis.. N Engl J Med. 2014. PMID 24836309. DOI 10.1056/NEJMoa1401739. (abstract)
Iversen HK. N-acetylcysteine enhances nitroglycerin-induced headache and cranial arterial responses.. Clin Pharmacol Ther. 1992. PMID 1505148. DOI 10.1038/clpt.1992.121. (abstract)
LactMed (NLM). Acetylcysteine (LactMed, NCBI Bookshelf record). Drugs and Lactation Database (LactMed). 2006. PMID 29999990. (abstract)
LiverTox (NIDDK). Acetylcysteine (LiverTox, NCBI Bookshelf record). LiverTox: Clinical and Research Information on Drug-Induced Liver Injury. 2012. PMID 31643720. (abstract)
Lizzo G, Migliavacca E, Lamers D, 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. PMID 35821844. DOI 10.3389/fragi.2022.852569. (abstract)
Pedre B, Barayeu U, Ezerina D, et al.. The mechanism of action of N-acetylcysteine (NAC): The emerging role of H(2)S and sulfane sulfur species.. Pharmacol Ther. 2021. PMID 34171332. DOI 10.1016/j.pharmthera.2021.107916. (abstract)
Peng TR, Lin HH, Tseng TL, et al.. Efficacy of N-acetylcysteine for patients with depression: An updated systematic review and meta-analysis.. Gen Hosp Psychiatry. 2024. PMID 39504621. DOI 10.1016/j.genhosppsych.2024.10.018. (abstract)
Poole P, Sathananthan K, Fortescue R. Mucolytic agents versus placebo for chronic bronchitis or chronic obstructive pulmonary disease.. Cochrane Database Syst Rev. 2019. PMID 31107966. DOI 10.1002/14651858.CD001287.pub6. (abstract)
Sahasrabudhe SA, Terluk MR, Kartha RV. N-acetylcysteine Pharmacology and Applications in Rare Diseases-Repurposing an Old Antioxidant.. Antioxidants (Basel). 2023. PMID 37507857. DOI 10.3390/antiox12071316. (abstract)
Shahveghar Asl Z, Parastouei K, Eskandari E. The effects of N-acetylcysteine on ovulation and sex hormones profile in women with polycystic ovary syndrome: a systematic review and meta-analysis.. Br J Nutr. 2023. PMID 36597797. DOI 10.1017/S0007114522003270. (abstract)
Syarif S, Makkaraka MAG, Zainal ATF, et al.. Unlocking the potential of antioxidant supplementation with n-acetylcysteine to improve seminal parameters and analysis of its safety: a systematic review and meta-analysis of randomized controlled trials.. Arch Ital Urol Androl. 2025. PMID 40126496. DOI 10.4081/aiua.2025.13750. (abstract)
Weisbord SD, Gallagher M, Jneid H, et al.. Outcomes after Angiography with Sodium Bicarbonate and Acetylcysteine.. N Engl J Med. 2018. PMID 29130810. DOI 10.1056/NEJMoa1710933. (abstract)
Yarema M, Chopra P, Sivilotti MLA, et al.. Anaphylactoid Reactions to Intravenous N-Acetylcysteine during Treatment for Acetaminophen Poisoning.. J Med Toxicol. 2018. PMID 29423816. DOI 10.1007/s13181-018-0653-9. (abstract)
Yolland CO, Hanratty D, Neill E, et al.. Meta-analysis of randomised controlled trials with N-acetylcysteine in the treatment of schizophrenia.. Aust N Z J Psychiatry. 2020. PMID 31826654. DOI 10.1177/0004867419893439. (abstract)
Zhou Y, Wu F, Shi Z, et al.. Effect of high-dose N-acetylcysteine on exacerbations and lung function in patients with mild-to-moderate COPD: a double-blind, parallel group, multicentre randomised clinical trial.. Nat Commun. 2024. PMID 39349461. DOI 10.1038/s41467-024-51079-1. (abstract)
. FDA: Releases Final Guidance on Enforcement Discretion for Certain NAC Products (constituent update; latest entry 2023-11-29). . . (full-text)
. MedlinePlus Drug Information: Acetylcysteine Oral Inhalation (last revised 2017-03-15). . . (full-text)

Where to buy

Check the label first. Whatever you buy, look for these:

The amount of the active ingredient per serving, not just the front-label claim
A third-party testing mark (USP, NSF or ConsumerLab)
Other ingredients and allergens
Ask a pharmacist about interactions with your medicines

Talk to a pharmacist or doctor before you start any supplement, especially if you take medicines. See the Safety tab for interactions.

Browse N-acetylcysteine on Amazon

Amazon · Several brands to compare

Shop N-acetylcysteine on Amazon

Support our free guides: as an Amazon Associate we earn from qualifying purchases. Full disclosure.

Education, not medical advice. This page is for general information. It does not diagnose or treat any condition and is not a substitute for care from a qualified health professional. Natural does not automatically mean safe. Ask a clinician or pharmacist before changing your care, especially if you take medication, are pregnant or breastfeeding, or have a health condition.