Short answer. NAC (N-acetylcysteine) is a form of the amino acid cysteine that the body uses to make glutathione, its main antioxidant inside cells. It has no RDA or upper limit. In studies lasting one to three years, adults took 600 to 1,200 mg a day, and only 6 to 10% of an oral dose reaches the blood unchanged (PMID 3803419).
NAC doses in studies at a glance
| Study | Who took part | Daily NAC and duration | What was reported |
|---|---|---|---|
| Borgström 1986 (PMID 3803419) | 10 healthy adults | One dose of 600 mg | Oral availability 6 to 10%; half-life about 2.27 hours |
| Hjortsø 1990 (PMID 2276385) | 10 healthy adults | 200 mg three times a day for two weeks | No change in blood or urine levels of calcium, magnesium, iron, zinc or copper |
| BRONCUS, Decramer 2005 (PMID 15866309) | 523 adults under medical care | 600 mg once a day for 3 years | Taken for three years under supervision |
| PANTHEON, Zheng 2014 (PMID 24621680) | 1,006 adults aged 40 to 80 under medical care | 600 mg twice a day (1,200 mg) for 1 year | Side effects in 29% on NAC and 26% on placebo |
| GlyNAC, Kumar 2023 (PMID 35975308) | 24 older adults (12 on GlyNAC) | 100 mg per kg of body weight of NAC plus the same amount of glycine for 16 weeks | Glutathione and oxidative stress markers improved; no supplement-related adverse events |
Source: PubMed abstracts and full text listed under Sources.
What is NAC and what does it do in the body?
N-acetylcysteine, usually shortened to NAC, is the amino acid cysteine with an acetyl group attached. It is not a vitamin or a mineral. After it is absorbed, the body breaks it down to cysteine, and cells use that cysteine to make glutathione (NIH StatPearls, NCBI Bookshelf).
Glutathione is built from three amino acids: glutamate, cysteine and glycine. It is the most abundant non-protein thiol in mammalian tissues and is a key part of the body's defense against oxidative stress. It also plays a role in the body's natural detoxification pathways and in immune function. A review by Lu (2013) names two main things that set how much glutathione a cell can make: how much cysteine is available and how active the first enzyme in the process, glutamate cysteine ligase, is (PMID 22995213).
NAC also has a separate life as a prescription medicine. Hospitals use it in emergency care and as an inhaled mucus-thinning agent, at doses many times higher than in supplements. For example, one hospital oral protocol adds up to 1,330 mg per kg of body weight over three days (NIH StatPearls). That use is for doctors to manage and is not a model for home use.
Is there a daily requirement for NAC for children and adults?
No. NAC does not appear in any of the Dietary Reference Intake tables, so there is no Recommended Dietary Allowance, Adequate Intake or upper limit for it. The body gets cysteine from protein in the diet, so the closest official reference point is the protein RDA. Getting enough protein is the first step before thinking about a cysteine-based supplement.
| Age | Protein, boys and men | Protein, girls and women | NAC RDA or upper limit |
|---|---|---|---|
| 0–6 months | 9.1 g (Adequate Intake) | 9.1 g (Adequate Intake) | Not established |
| 7–12 months | 11.0 g | 11.0 g | Not established |
| 1–3 years | 13 g | 13 g | Not established |
| 4–8 years | 19 g | 19 g | Not established |
| 9–13 years | 34 g | 34 g | Not established |
| 14–18 years | 52 g | 46 g | Not established |
| 19 years and older | 56 g | 46 g | Not established |
| Pregnancy | — | 71 g | Not established |
| Breastfeeding | — | 71 g | Not established |
Source: NIH, NCBI Bookshelf, Dietary Reference Intakes summary tables (National Academies). The adult protein RDA is based on 0.8 g of protein per kg of body weight.
How much NAC do adults usually take?
Because there is no official intake level, the best guide is the doses that have been studied for long periods. The two largest long-term trials used 600 mg once a day and 600 mg twice a day.
In the BRONCUS trial, 523 adults at 50 centers took 600 mg a day or a placebo and were followed for three years (PMID 15866309). In the PANTHEON trial, 1,006 adults aged 40 to 80 at 34 hospitals took one 600 mg tablet twice a day, 1,200 mg in total, or a placebo for one year (PMID 24621680). Both trials enrolled people under a doctor's care for a long-term lung condition, so they tell us about dose and tolerability over time, not about what NAC does for healthy people.
A meta-analysis of 13 studies with 4,155 participants compared doses up to 600 mg a day with doses above 600 mg a day. The risk of side effects did not rise with the higher doses (PMID 26324807). Results for the outcomes these trials measured were mixed: BRONCUS found no difference from placebo, while PANTHEON reported a difference, which is one more reason to see NAC as something to plan with a clinician.
How well is NAC absorbed?
Only a small share of oral NAC reaches the bloodstream unchanged. In a study of 10 healthy adults given a single 600 mg dose, oral availability was 6 to 10%, and the half-life in blood was about 2.27 hours (PMID 3803419). A second study gave 200, 600 or 1,200 mg to 10 healthy adults and found that the share absorbed rose with the dose. When the same people took 600 mg twice a day for 5 days, blood levels looked the same as after one dose, so NAC does not build up in the blood with daily use (PMID 2328298). A third study found an oral bioavailability of 4.0% for the free form and 9.1% for total NAC (PMID 3360052).
The authors explained the low numbers by NAC being broken down before it reaches the general circulation (PMID 2328298). Its breakdown products include cysteine, the part cells use for glutathione (NIH StatPearls).
NAC or glutathione: which one should you choose?
They take different routes. NAC supplies cysteine so cells can make their own glutathione. A glutathione supplement supplies the finished molecule, which for years was thought to be poorly absorbed.
In a 6-month trial of 54 non-smoking adults, 1,000 mg of glutathione a day raised glutathione levels by 30 to 35% in red blood cells, plasma and lymphocytes. A 250 mg dose raised levels by 17% in whole blood and 29% in red blood cells. Levels returned to baseline one month after stopping (PMID 24791752).
A different approach pairs NAC with glycine, another glutathione building block. In a 16-week trial, 24 older adults took either a glycine and NAC combination called GlyNAC or a placebo. At the start, red blood cell glutathione was 66 to 70% lower in the older adults than in young adults. The combination, and not the placebo, improved glutathione levels and oxidative stress markers. The dose was large: 100 mg per kg of body weight of each, or about 7,000 mg of NAC a day for a 70 kg adult. Participants reported no supplement-related adverse events, and liver and kidney blood tests did not rise (PMID 35975308). This was a small study, so it is a reason for more research rather than a plan for home use. Some ASDHelp formulas combine NAC with glycine or glutathione, as listed below. You can read more about glycine in its own ingredient guide.
Is NAC safe, and what are the side effects?
The most common side effects of oral NAC involve the digestive tract: nausea, vomiting, diarrhea, gas and acid reflux (NIH StatPearls). In the PANTHEON trial, 29% of people taking 1,200 mg a day for a year reported an adverse event, compared with 26% on placebo (PMID 24621680).
Some groups need a doctor's input first:
- People with asthma or a history of bronchospasm. Airway narrowing has been reported, mostly with intravenous NAC, and is more common in people with reactive airways (NIH StatPearls).
- People with an active stomach ulcer, because of a concern about bleeding with oral NAC (NIH StatPearls).
- Pregnant and breastfeeding women. NIH StatPearls notes no apparent reports of fetal risk, but the decision belongs with the clinician who manages the pregnancy.
In 10 healthy adults who took 200 mg three times a day for two weeks, blood and urine levels of calcium, magnesium, iron, zinc and copper did not change (PMID 2276385), so at that dose NAC did not appear to pull these minerals out of the body.
Does NAC interact with medicines?
- Nitroglycerin. NAC can strengthen the effect of nitroglycerin, which may lead to low blood pressure and headache (NIH StatPearls). In 11 healthy volunteers, NAC made nitroglycerin headache worse (median score 3 versus 1) (PMID 1505148). In a study of 200 patients, the combination caused side effects in 35%, mainly intolerable headache, almost twice as often as nitroglycerin alone (PMID 9120179). Anyone using nitroglycerin or another nitrate should take NAC only if their cardiologist agrees.
- Carbamazepine. NAC can lower blood levels of carbamazepine (NIH StatPearls). Ask the prescriber before combining them.
- Other products with NAC. Many liver, antioxidant and mitochondrial formulas contain NAC. Add up the amount from every product you take.
Can children take NAC?
NIH sources give no supplement dose of NAC for children, and the body handles it differently at the youngest ages: the half-life is about 11 hours in newborns compared with 5.6 hours in adults (NIH StatPearls). Most ASDHelp products that contain NAC give no children's dose on the label. Whether a child needs NAC at all, which product and how much is a question for the child's pediatrician.
Which ASDHelp products contain NAC?
Doses are copied from each label. There is no upper limit for NAC, so the useful check is the total from all products compared with the 600 to 1,200 mg a day used in the long-term studies above. For example, one scoop of MITOboost Protein Powder plus a serving of Detox Synergy gives 850 mg.
- MITOboost Protein Powder Strawberry: 600 mg of N-acetyl-L-cysteine per scoop (29.6 g). Label directions: 1 scoop once daily; no children's dose and not for infants. The label carries a California Proposition 65 warning.
- D-Tox Complex: 250 mg of NAC per 2 capsules, with vitamin C, zinc, selenium and R-lipoic acid. Label directions: 2 capsules a day with meals; no children's dose.
- Detox-Amino: 250 mg of NAC per 6 capsules, with glycine and L-glutathione. Label directions: 6 capsules a day between meals; no children's dose.
- Detox Synergy: 250 mg of NAC per 4 capsules, with glycine and reduced glutathione. Label directions: 4 capsules daily.
- Liquid Glutathione: 125 mg of NAC per 5 mL (about 1 teaspoon), with two forms of glutathione. Label directions: 5 mL one to two times a day; ask a healthcare professional before any use by minors.
- MITOboost: 100 mg of NAC per 4 capsules, with CoQ10 and alpha-lipoic acid. Label directions: adults, 4 capsules daily with food; children only as directed by a healthcare professional.
- Spectrum Neurotransmitter Support: 100 mg of NAC per scoop (about 17.9 g), with CoQ10, DHA and phosphatidylserine. Label directions are for children 4 years or older, one scoop in a drink; check with the pediatrician first.
Related reading: R-lipoic acid and vitamin C, two other antioxidant nutrients found in several of these formulas.
Questions to take to your doctor
- Does our diet already provide enough protein for each person's age, and is a cysteine supplement needed at all?
- If NAC makes sense, what daily total from all products is right for us, and for how long?
- Do asthma, a stomach ulcer, pregnancy or breastfeeding change whether NAC is a good idea?
- Do any of our medicines, such as nitroglycerin or carbamazepine, call for avoiding NAC?
Sources
- Ershad M et al. N-Acetylcysteine. StatPearls, NCBI Bookshelf (NIH), updated 2024. ncbi.nlm.nih.gov/books/NBK537183
- National Academies. Dietary Reference Intakes summary tables (NCBI Bookshelf). ncbi.nlm.nih.gov/books/NBK545442
- Lu SC. Glutathione synthesis. Biochim Biophys Acta 2013. PMID 22995213
- Borgström L et al. Pharmacokinetics of N-acetylcysteine in man. Eur J Clin Pharmacol 1986. PMID 3803419
- Borgström L, Kågedal B. Dose dependent pharmacokinetics of N-acetylcysteine after oral dosing to man. Biopharm Drug Dispos 1990. PMID 2328298
- Olsson B et al. Pharmacokinetics and bioavailability of reduced and oxidized N-acetylcysteine. Eur J Clin Pharmacol 1988. PMID 3360052
- Hjortsø E et al. Does N-acetylcysteine increase the excretion of trace metals (calcium, magnesium, iron, zinc and copper) when given orally? Eur J Clin Pharmacol 1990. PMID 2276385
- Decramer M et al. Effects of N-acetylcysteine on outcomes (BRONCUS): a randomised placebo-controlled trial. Lancet 2005. PMID 15866309
- Zheng JP et al. Twice daily N-acetylcysteine 600 mg (PANTHEON): a randomised, double-blind placebo-controlled trial. Lancet Respir Med 2014. PMID 24621680
- Cazzola M et al. Influence of N-acetylcysteine on exacerbations: a meta-analysis. Eur Respir Rev 2015. PMID 26324807
- Kumar P et al. Supplementing glycine and N-acetylcysteine (GlyNAC) in older adults: a randomized clinical trial. J Gerontol A Biol Sci Med Sci 2023. PMID 35975308
- Richie JP Jr et al. Randomized controlled trial of oral glutathione supplementation on body stores of glutathione. Eur J Nutr 2015. PMID 24791752
- Iversen HK. N-acetylcysteine enhances nitroglycerin-induced headache and cranial arterial responses. Clin Pharmacol Ther 1992. PMID 1505148
- Ardissino D et al. Effect of transdermal nitroglycerin or N-acetylcysteine, or both. J Am Coll Cardiol 1997. PMID 9120179
These statements have not been evaluated by the Food and Drug Administration. These products are not intended to diagnose, treat, cure or prevent any disease. This article is educational and is not medical advice.