NAC (N-Acetylcysteine)
Also known as: N-Acetylcysteine, N-Acetyl-L-cysteine, Acetylcysteine, NAC
Lower numbers = closer to natural. Higher numbers = more enhanced.
Why this rating?
NAC is a prodrug of the amino acid L-cysteine and a precursor to the antioxidant glutathione. It is a supportive/antioxidant supplement and an FDA-approved medicine (as an IV antidote for acetaminophen overdose and as a mucolytic). It does not build muscle, alter hormones, or directly enhance athletic performance. Rated 1 as a basic supportive supplement.
Overview
N-Acetylcysteine (NAC) is a prodrug of L-cysteine, the rate-limiting building block the body uses to make glutathione, its master antioxidant. In medicine it is FDA-approved as the intravenous/oral antidote for paracetamol (acetaminophen) overdose and as an inhaled/oral mucolytic that thins mucus. In the enhancement world it is used on-cycle as cheap liver and antioxidant support, especially alongside oral steroids.
Purpose & Use Cases
Glutathione / Antioxidant Support
Supplies cysteine to raise glutathione, supporting the liver's detox capacity and general antioxidant defence.
On-Cycle Liver Support
Commonly stacked with oral (17-alpha-alkylated) steroids as part of a liver-support protocol, typically alongside TUDCA.
Mucolytic (Medical)
FDA-approved to thin and loosen mucus in respiratory conditions.
Acetaminophen Antidote (Medical)
The FDA-approved IV/oral antidote for paracetamol (acetaminophen) overdose, a high, weight-based hospital regimen, not a supplement dose.
Benefits
- Raises glutathione (the body's master antioxidant)
- Cheap, well-tolerated liver/antioxidant support
- FDA-approved acetaminophen-overdose antidote and mucolytic
- Directly scavenges free radicals via its thiol group
- Commonly paired with TUDCA on oral-steroid cycles
Good to Know
NAC is really a glutathione delivery system
NAC is a prodrug of L-cysteine, and cysteine is the rate-limiting ingredient for making glutathione, the body's master antioxidant. That is the whole basis for its use as an acetaminophen antidote (it refills the glutathione the toxic metabolite burns through) and for on-cycle liver support.
It is an actual FDA-approved drug, not just a supplement
Beyond the supplement aisle, acetylcysteine is FDA-approved as the intravenous/oral antidote for paracetamol (acetaminophen) overdose and as a mucolytic that thins mucus. The medical antidote dose is a high weight-based hospital regimen, nothing like the 600-1,200 mg supplement dose.
The antioxidant-vs-training caveat
Training adaptations are partly driven by the oxidative stress a workout creates (hormesis). The theoretical concern is that megadosing antioxidants like NAC right around training could blunt that signal. The effect of NAC specifically is not well established and is debated, but it is why some people avoid large antioxidant doses in the immediate peri-workout window.
Dosage Guidelines
| Experience Level | Dosage Range |
|---|---|
| Beginner | 600 – 600 mg/day |
| Intermediate | 600 – 1200 mg/day |
| Advanced | 1200 – 1800 mg/day |
The 600-1,800 mg/day range is common supplement/community practice for antioxidant and on-cycle liver support (run through the oral portion of a cycle). This is separate from, and far lower than, the FDA acetaminophen-overdose antidote, which is a high weight-based (mg/kg) hospital protocol given IV or orally, and from mucolytic dosing. Oral bioavailability is low (~6-10%).
Side Effects
GI upset
commonNausea, vomiting or diarrhoea, most likely at higher oral doses.
Take with food; split the dose.
Unpleasant sulfur taste/smell
commonThe thiol group gives NAC a characteristic sulfur odour.
Use capsules; take with a drink.
Anaphylactoid reaction (IV)
commonFlushing/rash-type anaphylactoid reactions occur in roughly 3-7% of patients given IV acetylcysteine (the acetaminophen-antidote setting), most often with rapid infusion.
A hospital/IV concern, not relevant to oral supplement use; managed clinically by slowing the infusion rate.
General Mitigation Strategies
NAC is generally very well tolerated orally. Take with food and split larger doses to limit GI upset. Antioxidant timing nuance: some argue high-dose antioxidants taken right around training may blunt the beneficial exercise-induced ROS signalling that drives some adaptations, so a few users avoid dosing large amounts immediately pre/post-workout. The evidence for NAC specifically is limited and debated.
Support Supplements
Ancillary supplements commonly run alongside NAC (N-Acetylcysteine) to manage side effects, support the target tissue, or fill nutrient demands it creates.
TUDCA
The standard partner for on-cycle liver support with orals, TUDCA supports bile flow while NAC restores hepatic glutathione. Together they cover two different arms of liver protection.
- Dose
- TUDCA 500-1,000 mg/day; NAC 600-1,200 mg/day
- Timing
- Through the oral portion of the cycle
- When
- Neither makes oral steroids "safe". Dose/duration limits and bloodwork are the real protection.
Post Cycle Therapy (PCT)
Not hormonal. Does not affect the HPTA. No PCT required.
How It Works
NAC serves as a prodrug for L-cysteine, the limiting substrate for synthesis of glutathione, the body's main intracellular antioxidant. Its thiol (sulfhydryl) group also directly reduces free radicals. In acetaminophen overdose it replenishes hepatic glutathione so the toxic metabolite NAPQI can be conjugated and cleared. As a mucolytic, the thiol group cleaves disulfide bonds in mucus glycoproteins, reducing its viscosity.
Fundamentals
Reference on the practices relevant to NAC (N-Acetylcysteine): how they are done and where they go wrong. Not a recommendation to use it.
Legal Status
OTC dietary supplement (sold under FDA enforcement-discretion guidance, following a 2020-2022 dispute over whether NAC could legally be marketed as a supplement) and an FDA-approved prescription/OTC medicine, USA.
Legal status varies by country and changes over time. This is a general summary, not legal advice.
WADA Status
NAC / acetylcysteine is not on the WADA Prohibited List. It is an antioxidant precursor available as an OTC supplement and an approved medicine.