NAC (N-Acetyl Cysteine)New

Reviewed Sep 21, 2026

N-acetylcysteine (NAC) is the rate-limiting precursor that supplies cysteine for synthesis of glutathione (GSH), the body’s principal intracellular antioxidant, which is why NAC sits at the center of most glutathione-focused longevity protocols. In a 12-week randomized, double-blind, placebo-controlled trial in 68 adults with metabolic syndrome, NAC 1,800 mg/day (versus placebo) significantly raised serum glutathione (by roughly 81 µmol/L, p<0.001) and improved several metabolic markers: fasting glucose fell about 5.2 mg/dL (p=0.02), fasting insulin about 1.7 µIU/mL (p=0.006), insulin resistance (HOMA-IR) about 0.69 (p=0.005), and high-sensitivity CRP about 0.8 mg/L (p=0.003), with a small rise in HDL cholesterol (p=0.001); adiponectin, blood pressure and other lipids were unchanged (Panahi et al., Journal of Functional Foods, 2022). Much of the recent aging interest comes from GlyNAC — NAC combined with glycine, the other glutathione precursor. In a 16-week randomized, placebo-controlled trial in 24 older adults, GlyNAC (and not placebo) corrected red-cell glutathione deficiency and improved oxidative stress, mitochondrial fuel oxidation, inflammation, insulin resistance, gait speed, muscle strength and body composition (Kumar et al., J Gerontol A Biol Sci Med Sci, 2023), and a 2026 review summarizes short-term GlyNAC data in adults with type 2 diabetes showing roughly 30% higher mitochondrial fat oxidation, about 22% lower insulin resistance and about 25% lower plasma free fatty acids (Wang et al., Frontiers in Nutrition, 2026). These aging and metabolic findings are promising but come largely from small, single-center trials, and GlyNAC benefits waned after supplementation stopped — larger, longer, independent studies are needed, and GlyNAC-style effects should not be assumed from NAC alone. Typical supplemental doses range from 600 to 1,800 mg/day; NAC is generally well tolerated, with occasional GI upset, headache or a sulfur odor, and it should be used cautiously alongside anticoagulants or in active bleeding. This information is educational and is not medical advice or a claim to diagnose, treat, cure or prevent any disease — discuss supplementation with your physician, especially if you take other medications.