La N-acétylcystéine a un rôle réglé sans contestation possible : administrée à l'hôpital, elle est l'antidote du surdosage en acétaminophène et prévient l'essentiel des lésions hépatiques qu'une forte dose provoquerait sinon. Dans la bronchite chronique et la BPCO, elle agit comme mucolytique et réduit modestement les poussées, et il existe des données modérées dans quelques troubles psychiatriques comme la trichotillomanie. La glycine, un acide aminé que le corps fabrique mais pas toujours en abondance, dispose de petits essais pour s'endormir plus vite.
Le GlyNAC associe la glycine à la NAC. Chez les personnes âgées, il restaure le glutathion et améliore les marqueurs mitochondriaux et du vieillissement. Mais les essais sont petits et plusieurs sont monogroupes, si bien que l'allégation de longévité nécessite une réplication indépendante de plus grande ampleur.
Findings & Outcomes
What It Is
N-acetylcysteine, written NAC, is a slightly modified form of the amino acid cysteine. Cysteine tops the short list of amino acids the body runs short of when it builds glutathione, its main internal antioxidant. Glycine, a second amino acid, is one the body makes, though not always in the amount the body needs, so it counts as conditionally essential. Glutathione is assembled from 3 amino acids; cysteine and glycine supply two of them. Because those two are the limiting building blocks, supplying both together is called GlyNAC.
What It Does
NAC's only proven use is emergency: it is the hospital antidote for acetaminophen overdose. Strength is separate from endorsement, the firmest result is a hospital treatment, which is no reason to take NAC daily. Ranked from firmest to most preliminary:
- The acetaminophen overdose antidote is a high-dose hospital treatment given intravenously, timed to the poisoning.
- The mucolytic use in COPD is long-standing and dose-dependent. A standard 600 mg once-daily dose did not slow the long decline in lung function; the modest cut in flare-ups needs 600 mg twice daily.
- The psychiatric trials are newer and uneven: one positive result in adult trichotillomania that a later trial in children did not repeat, plus a small pooled improvement in depression.
- Glycine for sleep rests on a few small studies, using about 3 g before bed.
- GlyNAC for aging is the frontier. The markers move in the right direction, but the strongest single study is a 16-week randomized trial in a small group. Most of the work comes from one research team, and several of its trials had no control arm, so the longevity claim needs larger, independent replication.
The Research & Studies
Everything here is based on the research we have collected and checked, sorted into groups and ordered with the strongest evidence first. Click any claim to open the studies behind it.
Liver
NAC prevents most serious liver injury given within 8 to 10 hours of an acetaminophen overdose
If someone takes a dangerous overdose of acetaminophen, the hospital gives N-acetylcysteine, and given in time it stops most of the liver damage the overdose would otherwise cause. This is the best-established thing NAC does, and it happens in a hospital.
Prescott's 1979 report established intravenous N-acetylcysteine as the treatment of choice for paracetamol (acetaminophen) poisoning, showing that when it was given early after overdose, severe liver damage and death were largely prevented compared with the outcomes seen before an effective antidote existed. The mechanism is direct: a toxic dose of acetaminophen depletes hepatic glutathione, leaving the reactive metabolite NAPQI to injure liver cells, and NAC supplies cysteine so the liver can rebuild glutathione and detoxify it. The antidote's effectiveness falls the longer treatment is delayed, which is why it is a time-critical emergency treatment, not anything a supplement can substitute for.
Who this may not transfer to:Overdose treatment applies across sexes and has been standard clinical practice for decades in mixed populations.
This is an emergency hospital treatment at high, supervised doses, not a use for a daily supplement. A suspected overdose is a reason to contact emergency services or a poison center immediately. The supplement uses of NAC described elsewhere on this page are unrelated to this antidote role.
The study · 1
Prescott et al., Intravenous N-acetylcysteine: the treatment of choice for paracetamol poisoning · Br Med J 1979;2(6198):1097-1100
Respiratory
NAC 600 mg twice daily cut COPD exacerbations about 22% over a year
In chronic lung diseases like COPD and chronic bronchitis, taking NAC regularly leads to somewhat fewer flare-ups over a year. The benefit is modest and shows up best at the higher dose of 600 mg twice a day.
The 2019 Cochrane review of mucolytic agents versus placebo in chronic bronchitis and COPD found that regular use reduced exacerbations and led to a small reduction in disability, though the effect size has narrowed as larger, more recent trials have been added. The PANTHEON randomized trial, in 1,006 Chinese patients with moderate-to-severe COPD, gave 600 mg of NAC twice daily or placebo for one year and found the annual exacerbation rate fell from 1.49 to 1.16 (rate ratio 0.78, 95% CI 0.67 to 0.90). The high-dose benefit is more consistent than the standard-dose result.
Who this may not transfer to:COPD trial populations are heavily male-weighted, PANTHEON included, so the effect is best documented in men and less precisely estimated in women.
This is a reason a clinician managing COPD or chronic bronchitis might add NAC, at 600 mg twice a day, as an adjunct to standard inhaled therapy, not a replacement for it. It reduces flare-ups modestly; it is not a treatment that restores lung function.
The studies · 2
Poole et al., Mucolytic agents versus placebo for chronic bronchitis or chronic obstructive pulmonary disease (Cochrane review) · Cochrane Database Syst Rev 2019;5:CD001287
Zheng et al., Twice daily N-acetylcysteine 600 mg for exacerbations of COPD (PANTHEON) · Lancet Respir Med 2014;2(3):187-194
NAC 600 mg daily did not slow lung-function decline over three years
Taking a standard daily dose of NAC did not protect the lungs from getting weaker over the years in people with COPD. It did not preserve lung function, which was the main thing the trial set out to test.
BRONCUS randomized 523 patients with COPD to 600 mg of NAC daily or placebo for three years. The rate of decline in FEV1, the primary endpoint, did not differ between the groups, so a standard daily dose did not preserve lung function over time. A pre-specified subgroup analysis suggested fewer exacerbations in patients not taking inhaled corticosteroids, which pointed toward the exacerbation benefit later seen more clearly at higher doses, but the main lung-function result was a clear null.
Who this may not transfer to:The trial population was predominantly male, as COPD trials of this era generally were, so the null on lung-function decline is best documented in men.
This is the reason NAC is framed as an adjunct that may reduce flare-ups, not as a treatment that changes the long-term course of COPD. Anyone hoping it will protect lung function over the years should know the trial that tested that found no such effect.
The study · 1
Decramer et al., Effects of N-acetylcysteine on outcomes in COPD (BRONCUS) · Lancet 2005;365(9470):1552-1560
Anxiety And Stress
NAC left 56% of adults with trichotillomania much improved versus 16% on placebo
In one good trial, adults who compulsively pull out their hair pulled less when taking NAC than when taking a placebo. The result held up in that trial, though a later trial in children did not find the same benefit.
Grant and colleagues randomized 50 adults with trichotillomania to N-acetylcysteine (dosed up to 2,400 mg a day) or placebo for 12 weeks. The NAC group had significantly greater reductions on hair-pulling severity scales, and 56% were rated much or very much improved compared with 16% on placebo. The proposed mechanism is the effect of NAC on glutamate signaling in brain circuits involved in compulsive behavior. A later double-blind trial of NAC for trichotillomania in children and adolescents did not separate from placebo, so the adult finding has not generalized cleanly across age groups.
Who this may not transfer to:The sample was predominantly women, consistent with the condition's distribution, and included men; the effect is best documented in women.
This is a reasonable option to discuss with a clinician for adult trichotillomania, where the evidence is a single positive controlled trial, alongside, not instead of established behavioral approaches. The lack of a repeat effect in children means it should not be assumed to work at every age.
The study · 1
Grant et al., N-acetylcysteine, a glutamate modulator, in the treatment of trichotillomania: a double-blind, placebo-controlled study · Arch Gen Psychiatry 2009;66(7):756-763
How it works
Cysteine plus glycine for two weeks restored older adults' glutathione toward youthful levels
Older people tend to be low in glutathione, the body's main internal antioxidant. Giving the two amino acids needed to build it, cysteine and glycine, brought their glutathione back up toward the levels seen in younger people.
Sekhar and colleagues compared glutathione status in older versus younger adults and found the older group had substantially lower red-cell glutathione and higher oxidative stress. Supplementing cysteine (delivered as N-acetylcysteine) and glycine for two weeks restored the rate of glutathione synthesis and its concentration to levels comparable with the young, and reduced oxidative-stress markers. This established the mechanistic rationale for the later GlyNAC trials: that the age-related fall in glutathione reflects a shortage of its precursors, not a fixed loss of the capacity to make it.
Who this may not transfer to:The study used small mixed-sex groups and was not powered to compare the sexes, so the biochemical effect is not separately established in men and women.
This is the mechanism the GlyNAC longevity work is built on. It shows the precursors can restore a biochemical marker; whether restoring that marker produces clinical benefit is the separate question the outcome trials address, and those remain small.
The study · 1
Sekhar et al., Deficient synthesis of glutathione underlies oxidative stress in aging and can be corrected by dietary cysteine and glycine supplementation · Am J Clin Nutr 2011;94(3):847-853
Mood & stress
NAC gave a small improvement in depressive symptoms across five trials of 574 people
Across the trials that have tested it, adding NAC produced a small improvement in low mood. The effect is modest and it was mostly studied alongside standard treatment, not on its own.
Fernandes and colleagues pooled five randomized placebo-controlled trials (574 participants) of N-acetylcysteine in people with depressive symptoms, most of them as adjunctive treatment. NAC improved depressive symptoms and functionality significantly more than placebo, though the effect size was small and the trials were clinically varied in dose and population. The proposed basis is NAC's effects on glutathione, oxidative stress and glutamate, all of which have been implicated in mood disorders.
Who this may not transfer to:The pooled trials enrolled mixed-sex adult populations; the small benefit was measured across both sexes.
This is an emerging, adjunctive signal, not a stand-alone treatment for depression. It is something to weigh with a clinician alongside established care, not a reason to defer or replace evidence-based treatment for low mood.
The study · 1
Fernandes et al., N-acetylcysteine in depressive symptoms and functionality: a systematic review and meta-analysis · J Clin Psychiatry 2016;77(4):e457-e466
Longevity And Mortality
Les données de longévité du GlyNAC sont petites, principalement en groupe unique, et proviennent d'une seule équipe de recherche
Les études à l'appui des affirmations de longévité du GlyNAC sont petites et principalement réalisées par une seule équipe, et plusieurs n'avaient pas de groupe de comparaison. C'est un stade précoce normal pour un vrai constat, et cela signifie que des essais plus grands et indépendants sont ce qui tranchera la question.
La base de données probantes du GlyNAC pour le vieillissement est concentrée dans une série d'essais du groupe de Sekhar, résumés dans leur propre revue, comprenant des essais pilotes en ouvert et un petit essai randomisé. La cohérence des résultats entre ces études est un point en leur faveur, et la concentration dans un seul groupe, les petits effectifs et le recours à des protocoles à groupe unique sont les raisons pour lesquelles le domaine traite l'affirmation de longévité comme prometteuse, non établie. Des essais plus grands, conduits de façon indépendante et en aveugle dans des populations plus diverses sont la pièce manquante.
Who this may not transfer to:The underlying trials used small mixed-sex samples not powered for sex comparisons, so sex-specific effects are not established.
Lisez les affirmations de longévité du GlyNAC comme une hypothèse avec des données précoces encourageantes, non comme un résultat prouvé. C'est le contexte à garder à l'esprit avant d'adopter le protocole complet, et la raison de guetter les essais indépendants.
The study · 1
Sekhar, GlyNAC Supplementation Improves Glutathione Deficiency, Oxidative Stress, Mitochondrial Dysfunction, Inflammation, Aging Hallmarks, Metabolic Defects, Muscle Strength, Cognitive Decline, and Body Composition: Implications for Healthy Aging · J Nutr 2021;151(12):3606-3616
Le GlyNAC pendant 16 semaines a augmenté le glutathion et amélioré les marqueurs du vieillissement dans un essai de 24 personnes
Older adults who took glycine and NAC together for four months restored their glutathione and improved measures of their cells' energy production, inflammation and physical function. The results are encouraging and the trial was small.
Kumar et ses collègues ont rapporté un essai randomisé de 24 participants dans lequel des adultes âgés prenaient du GlyNAC ou un placebo pendant 16 semaines ; le groupe GlyNAC a amélioré la carence en glutathion, le stress oxydatif, le dysfonctionnement mitochondrial, l'inflammation, la fonction physique et de multiples marqueurs du vieillissement. Un essai pilote en ouvert antérieur chez des adultes âgés (avec une comparaison à des jeunes adultes, non un bras placebo) avait rapporté le même large schéma d'améliorations du glutathion, de la fonction mitochondriale, de la résistance à l'insuline, de la fonction endothéliale, de la génotoxicité, de la force musculaire et de la cognition. La base mécanistique est l'effet de restauration des précurseurs établi auparavant : fournir de la cystéine et de la glycine reconstruit le glutathion qui diminue avec l'âge.
Who this may not transfer to:The GlyNAC trials enrolled small mixed-sex groups of older adults and were not powered to compare the sexes, so the effect is not separately established in men and women.
Il s'agit d'un résultat précoce prometteur qui n'est pas encore une intervention de longévité établie. Les essais sont petits, monocentriques et proviennent principalement d'un seul groupe, quiconque envisageant le protocole devrait donc le traiter comme une option de pointe à peser avec un clinicien, et guetter les essais indépendants plus grands qui confirmeraient ou restreindraient l'effet.
The studies · 2
Kumar et al., Supplementing Glycine and N-Acetylcysteine (GlyNAC) in Older Adults Improves Glutathione Deficiency, Oxidative Stress, Mitochondrial Dysfunction, Inflammation, Physical Function, and Aging Hallmarks: A Randomized Clinical Trial · J Gerontol A Biol Sci Med Sci 2023;78(1):75-89
Kumar et al., GlyNAC supplementation in older adults improves glutathione deficiency, oxidative stress, mitochondrial dysfunction, inflammation, insulin resistance, endothelial dysfunction, genotoxicity, muscle strength, and cognition: Results of a pilot clinical trial · Clin Transl Med 2021;11(3):e372
Sleep
Glycine 3 g before bed helped people fall asleep faster in small trials
Taking around 3 grams of glycine before bed helped people fall asleep a little faster and feel less tired and groggy the next day. The studies were small, so this is a gentle, early signal, not a settled sleep aid.
A small single-blind crossover study by Bannai and colleagues in partially sleep-restricted healthy volunteers found that 3 g of glycine before bed reduced daytime sleepiness and fatigue and shortened reaction time on a psychomotor vigilance task the next day; the memory-recognition and arithmetic tasks did not differ from placebo. A companion review from the same group summarized earlier small trials in which 3 g of glycine at bedtime shortened sleep-onset latency and improved subjective sleep quality, and proposed a mechanism through a mild lowering of core body temperature via glycine's action at NMDA receptors. All of these studies are small and several come from the same research group.
Who this may not transfer to:The glycine daytime-performance data come from male participants only, so the next-day performance effects are not established in women.
Glycine at about 3 g before bed is cheap and generally well tolerated, so it is reasonable to try, while treating it as preliminary. Sleep-regularity habits and the better-studied options carry more weight for anyone with a persistent sleep problem.
The studies · 2
Bannai et al., The effects of glycine on subjective daytime performance in partially sleep-restricted healthy volunteers · Front Neurol 2012;3:61
Bannai & Kawai, New therapeutic strategy for amino acid medicine: glycine improves the quality of sleep · J Pharmacol Sci 2012;118(2):145-148
How It Works
Anatomy of the Practice
1In the liver, against an overdose
A toxic dose of acetaminophen uses up the liver glutathione faster than it can be replaced, leaving a reactive by-product that damages cells. NAC delivers cysteine quickly, the body rebuilds glutathione, and the by-product is cleared. Given early enough this prevents most of the liver injury, which is why NAC is the antidote kept in every emergency department.
2In the airways
NAC loosens mucus, the reason it is called a mucolytic. It also raises glutathione in lung tissue under constant oxidative load in chronic bronchitis and COPD. Over months this shows up as somewhat fewer flare-ups; day-to-day breathing changes little.
3In aging cells
Glutathione tends to fall with age, and mitochondria, the parts of the cell that turn fuel into energy, work less cleanly as it does. Supplying cysteine and glycine together raises glutathione back toward younger levels in older adults, and the mitochondrial and oxidative-stress markers move with it. Whether that adds up to a longer or healthier life is the open question the trials have not been large enough to answer.
The amino acid that most often limits how much glutathione gets built is cysteine, and NAC delivers it reliably. That shortage sits behind all three uses. NAC rebuilds the glutathione an overdose uses up in the liver, raises it in lung tissue under oxidative strain, and restores the pool that falls with age. Glycine is the third amino acid in the molecule, and older adults can run low on it too, so cysteine alone may not rebuild the full supply. The same glutathione-and-mitochondria thread ties these compounds to senolytics, while glycine links them to collagen.
Giving NAC in hospital for an overdose stands apart from anything on a supplement shelf. Its everyday uses (for mucus, mood, and aging) sit at ordinary supplement scale.
A supplement dose of NAC will not treat an acetaminophen overdose. A suspected overdose is a medical emergency: call emergency services or a poison center immediately.
How to Take Them
Ways to Do It
These are inexpensive, widely available supplements, and the way in depends on what you want from them. Food and the free options come first; the gram-scale combination protocol is the least-tested option here.
The body builds glutathione from ordinary protein. Sulfur-rich foods (eggs, garlic, onions, cruciferous vegetables) supply cysteine. Glycine is plentiful in collagen-rich cuts of meat, in bone broth, and in gelatin. A diet with enough good protein supplies the cysteine and glycine the body uses to build glutathione, the fair starting point.
Small trials used about 3 g of glycine before bed. People fell asleep a little faster and felt less groggy the next day. It is cheap, tastes faintly sweet, and dissolves in water. The evidence is preliminary and the effect is gentle. Better-studied sleep options are covered on the [sleep environment](/go/integrative/practice/sleep-environment) and [melatonin](/go/integrative/practice/melatonin) pages.
A common supplement dose is 600 to 1,200 mg a day, the range used for its mucolytic effect and in most of the psychiatric trials. Take it with food if it unsettles your stomach.
The trials paired glycine and NAC, each dosed to body weight: several grams of each a day, well above the glycine sleep dose. The trials behind it are small and unreplicated.
Both are sold as single-ingredient powders and capsules, and as proprietary blends and premium longevity labels. Third-party testing is what confirms a product contains what the label says. Powders let you match the gram-scale doses used in the trials more easily than capsules.
Go Deeper
- Senolytics: another aging-focused supplement with the same gap between an appealing mechanism and the size of trial that would settle it.
- Collagen: roughly a third glycine by weight, part of why glycine intake and collagen show up together.
- Asthma: where the inhaled form of acetylcysteine needs care.
The Chinese Medicine View
Glutathione, cysteine and glycine are 20th-century biochemistry, with no entry in the classical Chinese pharmacopoeia. The tradition offers only a loose resemblance, described here separately from the biochemistry and the trials.
Two TCM patterns partly overlap, and neither is an exact match. The first is the lung. Chinese medicine reads a productive, phlegm-heavy cough through the Lung, the Spleen, and a buildup of phlegm-damp. A practitioner treating that pattern works on the same problem a mucolytic acts on, by a different logic and different tools. The tradition would not hand everyone one cough remedy; it asks whether the phlegm runs thin and cold or thick and hot, and treats accordingly. A mucolytic, in the same way, does not suit every chest.
The second pattern is aging. The Kidney governs the deep constitutional reserve, Jing, that thins across a lifetime, and the tradition has long language for supporting the older, more depleted body. TCM's picture of age-related depletion of Kidney Jing loosely echoes the modern picture of falling glutathione, a resemblance, not the same thing. This resemblance is a way of thinking, not evidence; the case for NAC and glycine rests on the trials.
Cautions For This Practice
Extra restraintEverything to be aware of is here, in one place. This practice suits most healthy people; a few situations call for real care.
La NAC orale est généralement bien tolérée, les troubles gastriques étant l'effet le plus courant
La revue Cochrane sur les mucolytiques, qui a regroupé des essais à long terme de NAC orale dans la bronchite chronique et la BPCO, a constaté que les événements indésirables étaient globalement comparables entre la NAC et le placebo, avec des effets gastro-intestinaux les plus fréquemment rapportés. Ce profil de tolérabilité s'applique au supplément oral et est distinct de la forme inhalée (nébulisée), qui peut irriter les voies respiratoires et provoquer un bronchospasme chez les personnes sensibles, et de l'antidote intraveineux à haute dose utilisé pour les surdoses, où des réactions anaphylactoïdes peuvent survenir sous surveillance médicale.Poole et al., Mucolytic agents versus placebo for chronic bronchitis or chronic obstructive pulmonary disease (Cochrane review)
The inhaled form and asthma
Everything here concerns NAC taken by mouth. Nebulized, inhaled acetylcysteine can irritate the airways and trigger bronchospasm, a sudden tightening of the airways. The risk is highest in people with asthma or reactive airways. That caution applies to the inhaled medical product, used under supervision, separate from the oral supplement.
Stomach upset is the common effect
By mouth, NAC is generally well tolerated. The most common complaint is gastrointestinal (nausea, a queasy or full stomach, or looser stools) and it is more likely at higher doses. Taking it with food helps. NAC also has a distinct sulfur smell that some people find off-putting. Glycine at the sleep dose is usually easy on the stomach; the larger gram-scale doses in the GlyNAC protocol can cause loose stools.
Medicines and bleeding to raise with a clinician
NAC may add to the effect of blood-thinning medicines and of drugs that lower blood pressure, and it is sometimes paused before surgery for that reason. If you take an anticoagulant, a nitrate, or blood-pressure medication, or you have surgery coming up, tell the clinician managing you that you take it. This matters most at the higher, gram-scale doses of the combination protocol.
The combination protocol belongs with a clinician
The GlyNAC trials used several grams a day of each amino acid, dosed by body weight. The evidence behind those doses is small and unreplicated. Doing this well means a clinician who can check it against your other medicines and watch your response.
Start slow, be smart, read the research, and consult a professional if you have any concerns. This is here to inform your choice, not make it for you.
Common Questions
Is NAC proven for anything?
Yes, one use is proven: the overdose antidote. Its other uses, from the mucolytic to the psychiatric and anti-aging claims, rest on smaller, less certain trials.
What is GlyNAC, and does it slow aging?
A real anti-aging claim needs at least 2 independent teams, with no stake in the outcome, reproducing the result in larger trials. A marker moving in the right direction justifies a larger trial; it does not prove the outcome.
Can glycine help me sleep?
It is among the mildest sleep aids sold: low risk, and a small effect: people fell asleep a little faster in the ~3 g trials. It works best alongside melatonin or better sleep habits.
Is NAC safe to take every day?
Daily oral NAC is low-risk for most healthy adults. The two things that change that are your other medicines and how high the dose goes.
Explore Related
Other pages this one connects to, by the evidence they share, the outcomes they touch, and the ground they cover.
All 13 sources on this page independently checked and cross-referenced.
Thomas Dehli, Founder & Editor, Sacred Lotus
Sacred Lotus has published Chinese medicine reference material since 2001. Integrative pages are held to the same standard as the herb and formula library: cite the source, grade the claim at its real strength, and say where the research has not looked. This page is educational and it is not medical advice. Last reviewed and updated August 9, 2026.
Evidence strength
How confidently the research supports a claim. Strength describes the evidence, not our endorsement.