MetabolismThin

NAC, N-acetylcysteine

Also called: N-acetyl-L-cysteine, acetylcysteine, glutathione precursor.

A glutathione precursor and hospital antidote for acetaminophen, sold to "detoxify", with real trials on mucus and contradictory results in psychiatry.

Immunity Longevity Stress

What it is

NAC is an acetylated form of cysteine, the limiting amino acid in glutathione synthesis. In hospital, acetylcysteine serves as the antidote to acetaminophen poisoning by restoring glutathione and neutralizing the toxic metabolite. On store shelves, people buy it for the liver, "detox", the airways and mood.

What the label does not say

The trials that show something do not use the dose in the Canadian bottle. Health Canada caps it at 600 mg per day; the psychiatry trials used 1,200 to 2,400 mg per day according to Examine, and the chronic bronchitis trials used medication doses.
On mucus, the 2019 Cochrane review (38 trials, 10,377 adults with chronic bronchitis or COPD, on NAC, carbocysteine or erdosteine) reports fewer exacerbations: about eight people on a mucolytic for nine months to prevent one, with no important effect on quality of life or lung function, and the trials from the 1970s to 1990s showed more effect than the recent ones.
In psychiatry, the results are contradictory: a 2016 meta-analysis (5 trials, 574 participants) reports a moderate improvement in depressive symptoms (standardized difference of 0.37), another from 2020 (7 trials, 728 participants) finds no significant improvement in symptoms and more digestive effects, with a number needed to harm of 7.
No trial found tests a general "detox" or a benefit in a healthy person. The link with glutathione is real; the extrapolation to daily detoxification is not.
Regulatory status: in August 2022, the FDA concluded that NAC is excluded from the definition of a supplement because it had been authorized as a drug before being sold as a supplement, while announcing that it would tolerate marketing pending possible regulation. In Canada, it remains a natural health product under a monograph.

The forms on the shelf

N-acetyl-L-cysteine capsules: the common supplement form. The Health Canada monograph covers it as an antioxidant only, with a ceiling of 600 mg per day.
Acetylcysteine solution or injection: a medication; the antidote dose is 300 mg/kg intravenously over 20 to 21 hours, nothing like a capsule.
Effervescent tablets or powder: the same molecule. The drug monograph describes a slight unpleasant odour, inherent to the product.

Published reference values

No recommended intake: it is not a nutrient. Health Canada: at most 600 mg per day, with a meal, in adults.
Effects reported in the trials: nausea, diarrhea, digestive discomfort.
Contraindication in the Canadian monograph: do not use with antibiotics or nitroglycerin; medical advice in case of kidney stones.

When

With a meal according to Health Canada. The sulfur smell is part of the molecule.

Keep apart from

Nitroglycerin and antibiotics: a contraindication in the Health Canada monograph, not a simple matter of spacing.

To mention to a professional

Kidney stones, use of nitroglycerin or antibiotics, psychiatric disorder on medication, pregnancy and breastfeeding: check with a health care professional.

What it is sold for, and what the data show

NAC is sold for the liver, detox and immunity. The solid data concern the hospital antidote and, more modestly, chronic bronchitis exacerbations; in psychiatry, two meta-analyses contradict each other; no trial data support a detox in a healthy person, and the Canadian dose of 600 mg is below that of the trials.

From the plate first

NAC does not exist as such on the plate; the body makes glutathione from the cysteine in dietary protein.

Sources

Educational information, drawn from the sources above. It does not replace the advice of a health professional, who remains the reference for your situation, your medications, pregnancy or breastfeeding.