Mechanism of Action
N-acetylcysteine is a stabilised form of cysteine, a sulphur-containing amino acid. The acetyl group attached to the molecule shields it from oxidation, allowing it to reach the bloodstream intact.
Once absorbed, NAC releases cysteine, which enters cells. Glutathione, a tripeptide (a small protein made of three amino acids: glutamate, cysteine and glycine), is assembled there from these building blocks. Laboratory work identifies cysteine as the rate-limiting link in that production chain: it is the one that runs short first.
Also in the laboratory, NAC appears as a substrate of hepatic conjugation reactions, and as a precursor of taurine, a sulphur amino acid concentrated in the heart and muscles. These descriptions come from the bench: they are mechanisms, not effects measured in humans.
Key Benefits
- Strong
Less oxidative wear in the blood: in adults, a meta-analysis of twenty-eight controlled trials measures a drop in malondialdehyde, the reference marker of lipid peroxidation. The pooled trials use 400 to 2,000 mg per day.
- Strong
Fewer respiratory episodes: in adults followed for chronic bronchitis, three independent meta-analyses measure a 10 to 25% drop in their frequency. The authors place the sufficient dose at 600 mg per day, over at least three months, in the absence of confirmed airway obstruction.
- Moderate
Lower background inflammation: in adults, a meta-analysis of twenty-four randomised trials of oral supplementation measures a drop in C-reactive protein and interleukin-6, at doses of 400 to 2,000 mg per day.
Dosage & Forms
Cysteine can be delivered in several oral forms. Free L-cysteine oxidises rapidly in the digestive tract. NAC circumvents this obstacle through its protective acetyl group.
Oral clinical trials use doses of 400 to 2,000 mg per day, over durations ranging from one to eighty weeks. The most widespread single-intake format is 600 mg.
Singular delivers 600 mg per day, in a single intake: this is the maximum daily amount authorised in France for this substance. The material selected is an N-acetyl-L-cysteine of Ph. Eur. and USP grade, obtained by synthesis-fermentation from L-cysteine of non-animal origin, freely soluble in water.
In the Singular Formula
Inclusion rationale
Stabilised form of cysteine, selected because both direct routes fail: free L-cysteine oxidises spontaneously in the digestive tract, and glutathione taken as such is cleaved by intestinal peptidases before reaching the circulation. In laboratory work, cysteine is the rate-limiting link in glutathione synthesis; glycine, also present in the formula, supplies a second substrate. In adults, a meta-analysis of twenty-four randomised trials of oral supplementation measures a drop in C-reactive protein and interleukin-6, at doses of 400 to 2,000 mg per day. NAC is not a default component: the engine adds it only for certain profiles, at 600 mg per day, the maximum daily amount authorised in France for this substance.
Selected form
N-acetyl-L-cysteine of Ph. Eur. and USP grade, obtained by synthesis-fermentation from L-cysteine of non-animal origin. The acetyl group stabilises the molecule: free L-cysteine oxidises spontaneously, whereas the acetylated form stays intact in solution. Once absorbed, it releases cysteine, the sulphur amino acid that laboratory work describes as rate-limiting in glutathione synthesis. White crystalline powder, freely soluble in water.
Formula dosage
0 to 600 mg.
Dose expressed as active substance, excluding excipients and carriers of the raw material.
Synergies in the formula
Linked Biomarkers
Safety & Precautions
NAC has been used in Europe for several decades. A review of forty-one trials using 600 mg per day and above, up to 3,000 mg, concludes that the oral tolerability profile is comparable between standard and high doses, and the longest trials followed their participants for two to three years.
The adverse effects listed for the oral form are uncommon, between one case in a thousand and one in a hundred: digestive upset, headache, nausea, tinnitus, allergic reactions, low blood pressure. Bleeding is rare, fewer than one case in a thousand.
The Singular formula sets NAC aside during pregnancy and breastfeeding, for want of sufficient data, during ongoing anticancer treatment, and with nitrate derivatives: combined with nitroglycerin, NAC causes intense headaches and drops in blood pressure. It is also set aside in cases of asthma, as a precaution.
Medical advice is recommended before use in cases of a history of digestive ulceration or hepatic or renal failure. NAC's effect on coagulation has been observed by the intravenous route in major surgery, not at standard oral doses; people taking an anticoagulant should nonetheless seek advice from a healthcare professional.
Scientific Studies
| Authors | Year | Type | Journal | |
|---|---|---|---|---|
| Askari M et al. | 2020 | Meta-analysis | Cytokine | View on PubMed |
The effects of N-Acetylcysteine on serum level of inflammatory biomarkers in adults. Findings from a systematic review and meta-analysis of randomized clinical trials Meta-analysis of 24 randomised trials (1,057 participants) covering oral supplementation only, at doses of 400 to 2,000 mg per day and over durations of 1 to 80 weeks. It measures a drop in C-reactive protein (−0.61 mg/L) and interleukin-6 (−0.43 pg/mL). Other inflammatory markers do not move. | ||||
| Faghfouri AH et al. | 2020 | Meta-analysis | European Journal of Pharmacology | View on PubMed |
The effects of N-acetylcysteine on inflammatory and oxidative stress biomarkers: A systematic review and meta-analysis of controlled clinical trials Meta-analysis of 28 controlled trials, all routes of administration combined, at doses of 400 to 2,000 mg per day. It measures a drop in malondialdehyde, interleukin-8 and homocysteine. On inflammation, its reading is finer than that of the oral meta-analysis: it finds no effect on interleukin-6 when pooling all trials, but does find one in the subgroup of trials at 1,200 mg per day or less. On C-reactive protein, however, it finds nothing — this is the field's point of disagreement, and it is published here as it stands. | ||||
| Kumar P et al. | 2023 | Randomised Controlled Trial | The Journals of Gerontology: Series A | View on PubMed |
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 Sixteen-week randomised controlled trial in 24 older adults, 12 per group. The glycine + NAC pairing is given at 100 mg per kilogram per day of each, that is roughly 7 g of NAC for a 70 kg adult — more than ten times the dose Singular delivers. The authors report gains in strength and gait speed; the six-minute walking distance shows only a trend. | ||||
| Lizzo G et al. | 2022 | Randomised Controlled Trial | Frontiers in Aging | View on PubMed |
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 Controlled trial in 114 healthy adults, mean age 65, with three doses of the glycine + NAC pairing over two weeks. The primary endpoint — a rise in glutathione — was not met. Only a subgroup defined after the fact, with high oxidative stress and low baseline glutathione, showed a response. This is the largest trial in the field, and it does not replicate the pilot findings. | ||||
| Cazzola M et al. | 2015 | Meta-analysis | European Respiratory Review | View on PubMed |
Influence of N-acetylcysteine on chronic bronchitis or COPD exacerbations: a meta-analysis Meta-analysis of 13 trials and 4,155 patients, explicitly comparing low doses (600 mg per day or less) with high ones. It measures a drop in episode frequency, and concludes that in the absence of airway obstruction "a regular treatment of 600 mg per day seems to be sufficient". Two later meta-analyses, in 2019 and 2024, find the same order of magnitude in this population. | ||||
| Zhou Y et al. | 2024 | Randomised Controlled Trial | Nature Communications | View on PubMed |
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 The largest and longest trial in the field: 968 participants, two years, 1,200 mg per day. It is negative, on episode frequency as well as on lung function. It covers the form with confirmed airway obstruction, where a three-year trial at 600 mg per day was already negative — hence the limit stated in the benefit above. | ||||