La N-acetilcisteína tiene un papel resuelto más allá de toda discusión: administrada en el hospital, es el antídoto para la sobredosis de acetaminofén y previene la mayor parte de la lesión hepática que una dosis alta causaría de otro modo. En la bronquitis crónica y la EPOC funciona como mucolítico y reduce de forma modesta las reagudizaciones, y hay evidencia moderada en algunas afecciones psiquiátricas como la tricotilomanía. La glicina, un aminoácido que el cuerpo produce pero no siempre en abundancia, cuenta con pequeños ensayos para conciliar el sueño más rápido.
El GlyNAC combina la glicina con la NAC. En adultos mayores restaura el glutatión y mejora los marcadores mitocondriales y de envejecimiento. Pero los ensayos son pequeños y varios son de un solo grupo, así que la afirmación sobre la longevidad necesita replicación independiente y de mayor tamaño.
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
La NAC previene la mayoría del daño hepático grave cuando se administra dentro de las 8 a 10 horas de una sobredosis de paracetamol
Si alguien toma una sobredosis peligrosa de paracetamol, el hospital administra N-acetilcisteína, y dada a tiempo detiene la mayor parte del daño hepático que la sobredosis causaría de otro modo. Esto es lo mejor establecido que hace la NAC, y ocurre en un hospital.
El informe de Prescott de 1979 estableció la N-acetilcisteína intravenosa como el tratamiento de elección para la intoxicación por paracetamol (acetaminofén), mostrando que cuando se administraba tempranamente tras la sobredosis, el daño hepático grave y la muerte se prevenían en gran medida en comparación con los resultados observados antes de que existiera un antídoto eficaz. El mecanismo es directo: una dosis tóxica de paracetamol agota el glutatión hepático, dejando al metabolito reactivo NAPQI dañar las células hepáticas, y la NAC aporta cisteína para que el hígado pueda reconstruir el glutatión y desintoxicarlo. La eficacia del antídoto disminuye cuanto más se retrasa el tratamiento, razón por la cual es un tratamiento de urgencia crítico en el tiempo, no algo que un suplemento pueda sustituir.
Who this may not transfer to:Overdose treatment applies across sexes and has been standard clinical practice for decades in mixed populations.
Este es un tratamiento hospitalario de urgencia a dosis altas y supervisadas, no un uso para un suplemento diario. Una sospecha de sobredosis es una razón para contactar a los servicios de emergencia o a un centro toxicológico de inmediato. Los usos como suplemento de la NAC descritos en otras partes de esta página no están relacionados con este papel de antídoto.
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
La NAC 600 mg dos veces al día redujo las exacerbaciones de EPOC aproximadamente un 22 % a lo largo de un año
En enfermedades pulmonares crónicas como la EPOC y la bronquitis crónica, tomar NAC regularmente lleva a algo menos de exacerbaciones a lo largo de un año. El beneficio es modesto y se muestra mejor con la dosis más alta de 600 mg dos veces al día.
La revisión Cochrane de 2019 de agentes mucolíticos frente a placebo en la bronquitis crónica y la EPOC encontró que el uso regular redujo las exacerbaciones y llevó a una pequeña reducción de la discapacidad, aunque el tamaño del efecto se ha reducido a medida que se han añadido ensayos más grandes y recientes. El ensayo aleatorizado PANTHEON, en 1006 pacientes chinos con EPOC de moderada a grave, dio 600 mg de NAC dos veces al día o placebo durante un año y encontró que la tasa anual de exacerbaciones bajó de 1.49 a 1.16 (razón de tasas de 0.78; IC del 95 %: 0.67 a 0.90). El beneficio de la dosis alta es más consistente que el resultado de la dosis estándar.
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.
Esta es una razón por la que un clínico que maneja la EPOC o la bronquitis crónica podría añadir NAC, a 600 mg dos veces al día, como complemento a la terapia inhalada estándar, no como reemplazo de ella. Reduce modestamente las exacerbaciones; no es un tratamiento que restaure la función pulmonar.
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
La NAC 600 mg diarios no ralentizó el declive de la función pulmonar a lo largo de tres años
Tomar una dosis diaria estándar de NAC no protegió a los pulmones de debilitarse con los años en personas con EPOC. No preservó la función pulmonar, que era lo principal que el ensayo se propuso probar.
BRONCUS asignó aleatoriamente a 523 pacientes con EPOC a 600 mg de NAC al día o placebo durante tres años. La tasa de declive del VEF1, el criterio de valoración primario, no difirió entre los grupos, por lo que una dosis diaria estándar no preservó la función pulmonar con el tiempo. Un análisis de subgrupo preespecificado sugirió menos exacerbaciones en pacientes que no tomaban corticoides inhalados, lo cual apuntaba hacia el beneficio en las exacerbaciones observado más claramente después con dosis más altas, pero el resultado principal de función pulmonar fue claramente nulo.
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.
Esta es la razón por la que la NAC se enmarca como un complemento que puede reducir las crisis, no como un tratamiento que cambia el curso a largo plazo de la EPOC. Cualquiera que espere que proteja la función pulmonar a lo largo de los años debe saber que el ensayo que probó eso no encontró tal efecto.
The study · 1
Decramer et al., Effects of N-acetylcysteine on outcomes in COPD (BRONCUS) · Lancet 2005;365(9470):1552-1560
Anxiety And Stress
La NAC dejó al 56 % de los adultos con tricotilomanía muy mejorados frente al 16 % con placebo
En un buen ensayo, los adultos que se arrancan compulsivamente el cabello se lo arrancaron menos al tomar NAC que al tomar un placebo. El resultado se sostuvo en ese ensayo, aunque un ensayo posterior en niños no encontró el mismo beneficio.
Grant y colaboradores asignaron aleatoriamente a 50 adultos con tricotilomanía a N-acetilcisteína (dosificada hasta 2400 mg al día) o placebo durante 12 semanas. El grupo de NAC tuvo reducciones significativamente mayores en las escalas de gravedad de arrancarse el cabello, y el 56 % fue calificado como mucho o muy mejorado en comparación con el 16 % con placebo. El mecanismo propuesto es el efecto de la NAC sobre la señalización de glutamato en los circuitos cerebrales implicados en la conducta compulsiva. Un ensayo doble ciego posterior de NAC para la tricotilomanía en niños y adolescentes no se separó del placebo, por lo que el hallazgo en adultos no se ha generalizado limpiamente entre grupos de edad.
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.
Esta es una opción razonable para discutir con un clínico para la tricotilomanía en adultos, donde la evidencia es un único ensayo controlado positivo, junto a, no en lugar de, los enfoques conductuales establecidos. La falta de un efecto repetido en niños significa que no debe asumirse que funciona a cualquier edad.
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
La NAC dio una pequeña mejora en los síntomas depresivos en cinco ensayos de 574 personas
En los ensayos que la han probado, añadir NAC produjo una pequeña mejora en el ánimo bajo. El efecto es modesto y se estudió principalmente junto al tratamiento estándar, no por sí sola.
Fernandes y colaboradores combinaron cinco ensayos aleatorizados controlados con placebo (574 participantes) de N-acetilcisteína en personas con síntomas depresivos, la mayoría como tratamiento complementario. La NAC mejoró los síntomas depresivos y la funcionalidad significativamente más que el placebo, aunque el tamaño del efecto fue pequeño y los ensayos fueron clínicamente variados en dosis y población. La base propuesta son los efectos de la NAC sobre el glutatión, el estrés oxidativo y el glutamato, todos los cuales se han implicado en los trastornos del ánimo.
Who this may not transfer to:The pooled trials enrolled mixed-sex adult populations; the small benefit was measured across both sexes.
Esta es una señal emergente y complementaria, no un tratamiento independiente para la depresión. Es algo que sopesar con un clínico junto a la atención establecida, no una razón para posponer o reemplazar el tratamiento basado en evidencia para el ánimo bajo.
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
GlyNAC's longevity evidence is small, mostly single-group, and from one research team
The studies behind the GlyNAC longevity claims are small and mostly done by one team, and several had no comparison group. That is a normal early stage for a real finding, and it means bigger, independent trials are what will settle it.
The GlyNAC evidence base for aging is concentrated in a series of trials from Sekhar's group, summarized in their own review, spanning open-label pilots and a small randomized trial. The consistency of the findings across those studies is a point in their favor, and the concentration in one group, the small sample sizes, and the reliance on single-group designs are the reasons the field treats the longevity claim as promising, not established. Larger, independently run, blinded trials in more diverse populations are the missing piece.
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.
Read the GlyNAC longevity claims as a hypothesis with encouraging early support, not a proven result. This is the context to keep in mind before adopting the full protocol, and the reason to watch for independent trials.
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
GlyNAC for 16 weeks raised glutathione and improved aging markers in a 24-person trial
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 and colleagues reported a 24-participant randomized trial in which older adults took GlyNAC or placebo for 16 weeks; the GlyNAC group improved glutathione deficiency, oxidative stress, mitochondrial dysfunction, inflammation, physical function and multiple aging hallmarks. An earlier open-label pilot in older adults (with a comparison to young adults, not a placebo arm) had reported the same broad pattern of improvements in glutathione, mitochondrial function, insulin resistance, endothelial function, genotoxicity, muscle strength and cognition. The mechanistic basis is the precursor-restoration effect established earlier: supplying cysteine and glycine rebuilds the glutathione that falls with age.
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.
This is a promising early result and it is not yet a settled longevity intervention. The trials are small, single-center and largely from one group, so anyone considering the protocol should treat it as a frontier option to weigh with a clinician, and watch for the larger independent trials that would confirm or narrow the effect.
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
Tomar alrededor de 3 gramos de glicina antes de dormir ayudó a las personas a conciliar el sueño un poco más rápido y a sentirse menos cansadas y aturdidas al día siguiente. Los estudios fueron pequeños, por lo que esta es una señal suave y temprana, no un remedio para el sueño asentado.
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.
Oral NAC is generally well tolerated, with stomach upset the most common effect
The Cochrane review of mucolytics, which pooled long-term oral NAC trials in chronic bronchitis and COPD, found adverse events were broadly comparable between NAC and placebo, with gastrointestinal effects the most frequently reported. This tolerability profile applies to the oral supplement and is distinct from the inhaled (nebulized) form, which can irritate the airways and provoke bronchospasm in susceptible people, and from the high-dose intravenous antidote used for overdose, where anaphylactoid reactions can occur under medical supervision.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.