Bi-Layer Tablets Glutathione Precursor Glutathione is Important for Detoxification Quick + Sustained Release Non-gmo Gluten Free Dietary Supplement Liver Support Jarrow Formulas Nac Sustain features N-Acetyl- L-Cysteine (NAC), an antioxidant amino acid and a precursor to glutathione. Glutathione is important for detoxification. The advanced bi-layer Sustain tablets combine 1/3 Quick Release with 2/3 Sustained Release formats to release NAC over time.