NAC (N-Acetyl Cysteine) Dosage Calculator

What is NAC (N-Acetyl Cysteine)?

N-Acetyl Cysteine (NAC) is an acetylated form of the amino acid L-cysteine, developed in the 1960s as a pharmaceutical mucolytic agent. It serves as the direct precursor for intracellular glutathione (GSH) synthesis — the body's most abundant endogenous antioxidant, present in virtually every cell. By providing cysteine (the rate-limiting substrate for the gamma-glutamylcysteine synthetase reaction), NAC replenishes GSH depleted by oxidative stress, toxins, or illness. It also has direct antioxidant activity, scavenging free radicals via its thiol (-SH) group, and anti-inflammatory effects by inhibiting NF-κB. Clinically established uses: IV NAC is the standard emergency treatment for paracetamol (acetaminophen) overdose; inhaled NAC thins mucus in COPD and cystic fibrosis; oral NAC has evidence for OCD (2,400 mg/day), addiction cravings (cigarettes, cocaine), PCOS, and contrast-induced nephropathy prevention.

How to Take NAC (N-Acetyl Cysteine)

Supplement doses range from 600–1,800 mg/day depending on the indication. **600 mg/day:** General antioxidant support, liver protection, respiratory health maintenance. **1,200 mg/day (600 mg twice daily):** PCOS, fertility support, moderate oxidative stress conditions. **1,800–2,400 mg/day:** OCD (clinical trial dose), addiction support, chronic respiratory disease — under physician oversight at these levels. Always start at the lowest effective dose (600 mg once daily with food) and assess tolerance for 1–2 weeks before increasing. NAC has a strong sulphurous odour and taste; taking it with juice or flavoured liquid improves palatability.

Timing Recommendations

NAC is best taken with meals to reduce GI discomfort. For sleep quality, some evidence and anecdotal reports support evening dosing (NAC may support GABAergic tone via glutamate modulation). For athletic recovery, post-exercise dosing may reduce exercise-induced oxidative stress, though high-dose antioxidant supplementation during training adaptation phases is debated. Split twice-daily dosing (morning + evening) is preferred over a single large dose for doses ≥ 1,200 mg.

Potential Side Effects & Safety

GI side effects (nausea, vomiting, diarrhoea) are the most common at doses > 1,200 mg/day, especially when taken on an empty stomach. Rare: urticaria and bronchospasm (more common with IV administration). There is theoretical concern that very high doses of antioxidants may blunt hormetic adaptation signals from exercise — avoid taking > 1,200 mg/day immediately before or after training sessions if hypertrophy is a goal. The FDA reclassified NAC in 2020, removing it from OTC dietary supplement status in the US (it had been sold as a supplement since 1994); the regulatory situation remains in flux, but it remains widely available.

Best Stacks with NAC (N-Acetyl Cysteine)

NAC + alpha-lipoic acid (ALA) + CoQ10 form the "antioxidant network" stack: NAC rebuilds intracellular glutathione, ALA regenerates vitamins C and E, and CoQ10 supports mitochondrial electron transport. For liver protection during medication use or alcohol consumption, NAC combined with milk thistle (silymarin) addresses both GSH replenishment and hepatocyte membrane stabilisation.

Scientific References

All dosage recommendations are grounded in peer-reviewed research.

1. 1
   N-Acetylcysteine: A Review of Clinical Use and Efficacy

   Nutrients · 2021

2. 2
   Randomized trial of N-acetylcysteine for obsessive-compulsive disorder

   Journal of Clinical Psychiatry · 2012