NAC is the supplement most people take to top up their body's main internal antioxidant, glutathione. It's a stable form of the amino acid cysteine, which is the rate-limiting ingredient your cells need to make glutathione. Swallow it, your liver and tissues use the cysteine to build more glutathione, and the downstream effects show up in liver function, lung mucus clearance, hangover recovery, skin, and a long list of psychiatric and metabolic conditions where oxidative stress is part of the picture.

Most people pick it up for one of four reasons: to support the liver during heavy drinking, paracetamol use, or any period of elevated toxin load; to thin mucus and reduce flare-ups in chronic bronchitis or COPD; to help with compulsive behaviours like hair-pulling, skin-picking, or nail-biting where it has surprisingly good trial data; or to support fertility in PCOS. It's cheap, well-tolerated, sold over the counter in most countries, and has a pharmacy-grade history (it's the standard hospital antidote for paracetamol overdose), which is unusual for something also marketed as a supplement.

Deep-dive

Dosage:

• General antioxidant / liver support / daily use: 600-1,200 mg per day, taken as 600 mg once or twice daily. This is the dose used in most respiratory trials and the floor of most other uses. Effects on glutathione stores typically take 2-4 weeks to fully establish
• COPD / chronic bronchitis / mucus thinning: 600 mg twice daily (1,200 mg/day total). Higher doses up to 1,800 mg/day appear more effective at reducing exacerbations than the lower 600 mg/day dose. Take with water, increased fluid intake amplifies the mucolytic effect
• Trichotillomania / skin-picking / nail-biting: Start at 1,200 mg/day in two divided doses, titrate up to 2,400 mg/day after 4-6 weeks if no response. Give it at least 12 weeks before deciding it's not working. The benefit, when it appears, is gradual
• OCD augmentation: 2,400-3,000 mg/day in divided doses as an add-on to standard SSRI treatment. Don't expect a dramatic effect, results are mixed and modest
• PCOS: 1,200-1,800 mg/day, often combined with inositol (2-4 g/day of myo-inositol) and folic acid. Continue for at least 3-6 months for fertility outcomes
• Male fertility: 600 mg/day for 3-6 months, ideally stacked with selenium (100-200 mcg) or zinc (15-30 mg)
• GlyNAC longevity protocol: 100 mg/kg/day each of NAC and glycine, split into two doses morning and evening. For a 70 kg adult, that's about 3.5 g of each twice daily. This is significantly higher than the standalone NAC dose but is what the Baylor protocol uses
• Hangover prevention or recovery: 600-1,200 mg taken before or with alcohol, repeat the next morning. Won't make heavy drinking safe but does reduce the oxidative burden on the liver. Pairing with glycine and vitamin C is common
• Timing: Take with food if you get GI upset, otherwise empty stomach absorbs slightly better. NAC has a sulfur smell some people find unpleasant, capsules mask it better than powder
• Forms: Standard NAC capsules work fine. Effervescent NAC (the European pharmaceutical form, sold as Fluimucil or similar) is the most bioavailable oral form. Liposomal NAC exists but the evidence it outperforms standard isn't strong enough to justify the price. Avoid NAC sustained-release formulations, the data is on immediate-release
• Cycling: Not necessary. Glutathione synthesis has feedback inhibition built in, so once you've topped up the system, more NAC doesn't keep pushing it higher. Daily use is what the trials studied

Here's what you can expect:

For the typical respiratory use (chronic mucus, smoker's cough, recurring bronchitis), the effect tends to show up within 2-4 weeks as thinner mucus that clears more easily. Fewer flare-ups across a winter or year is the more meaningful endpoint, harder to feel day-to-day but real on the data.

For liver support around drinking or paracetamol use, the subjective signal is usually "hangovers feel less brutal" and "I bounce back faster."