Rankings / Essentials — Supplements

NAC (N-acetyl cysteine)

Essentials · Glutathione precursor / mucolytic

Also known as: Acetylcysteine ·Mucomyst

Tier B+

Reviewed by Read Off Label · Last reviewed · How we grade

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7.1 / 10
Tier B+
Ev 6 Bn 5 Sf 9

Bottom line

Read Off Label grades NAC (N-acetyl cysteine) as B+ (7.1/10) based on moderate evidence, moderate benefit magnitude, and a low-risk safety profile.

Core component of the GlyNAC longevity combination (with glycine).

Studied, labeled, or reported-use context: 600-1800 mg/day PO divided; higher for acute liver protection — Rx (IV for APAP overdose; Mucomyst); OTC supplement; not individualized guidance.

What the evidence says

Core component of the GlyNAC longevity combination (with glycine). Human studies report respiratory and glutathione-related effects; clinical outcome evidence varies by indication and does not substantiate broad "detox" claims. Used medically IV for acetaminophen overdose. FDA sent warning letters to Amazon sellers in 2020 claiming NAC was an unapproved drug — triggering industry litigation — then issued a 2022 final rule backing off enforcement, and NAC remains widely sold. Can cause transient nausea at high doses. A 2026 randomized trial in 60 non-diabetic adults with metabolic-dysfunction-associated steatotic liver disease (MASLD) gave 2,400 mg/day for 12 weeks on top of lifestyle advice and found nothing: no difference against lifestyle alone in oxidative stress (malondialdehyde), insulin resistance (HOMA-IR, fasting insulin, leptin), or liver steatosis and fibrosis on FibroScan. HDL rose in the NAC arm and triglycerides fell in the control arm. NAC was safe and well tolerated. The trial was open-label, which limits it, but it is a clean null for the hepatoprotective claim at a high dose and is worth weighing against the more positive NASH literature.

Mechanism

Cysteine prodrug; replenishes glutathione (rate-limited by cysteine availability); mucolytic via disulfide bond reduction; glutamate modulation in brain; anti-inflammatory; FDA-approved for acetaminophen overdose and as mucolytic

Studied, labeled, or reported dose & route

600-1800 mg/day PO divided; higher for acute liver protection

This records doses and routes described in studies, approved labeling, clinical practice, or documented use. It is not individualized guidance and does not establish safety; context changes with indication, formulation, health history, monitoring, and other medicines.

Citations

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Common questions

What does the evidence show about NAC (N-acetyl cysteine)'s effects?
Read Off Label rates the evidence for NAC (N-acetyl cysteine) as Moderate and the benefit magnitude as moderate, producing an overall grade of B+ (7.1/10). Core component of the GlyNAC longevity combination (with glycine).
What safety findings are reported for NAC (N-acetyl cysteine)?
NAC (N-acetyl cysteine) has a low risk profile in the database. Low (GI upset; rotten-egg smell characteristic; bronchospasm with inhaled form) Legal status: Rx (IV for APAP overdose; Mucomyst); OTC supplement (restored after FDA 2022 decision not to pursue enforcement action after 2020 warning letters).
What doses or routes are reported for NAC (N-acetyl cysteine)?
600-1800 mg/day PO divided; higher for acute liver protection This is context from studies, approved labeling, clinical practice, or documented use; it is not individualized guidance and does not establish safety.
How does NAC (N-acetyl cysteine) work?
Cysteine prodrug; replenishes glutathione (rate-limited by cysteine availability); mucolytic via disulfide bond reduction; glutamate modulation in brain; anti-inflammatory; FDA-approved for acetaminophen overdose and as mucolytic

This is an independent synthesis of published research by a non-clinician. Scores are opinions supported by citations, not prescriptions. See the full disclaimer and methodology for how this score was produced and what it does and doesn't mean.