From the Manufacturer:
NAC Sustain® is in a special Sustain™ bilayer Quick Release/Sustained Release format of N-Acetyl-L-Cysteine (NAC), a powerful antioxidant amino acid and a precursor to the critical antioxidant glutathione.* Substances known to reduce glutathione status are acetaminophen and alcohol.*
The advanced bilayer Sustain™ tablets combine 1/3 Quick Release and 2/3 Sustained Release formats to both immediately raise and maintain blood levels over a longer period of time.* NAC Sustain® releases in the small intestine over an 8 hour period, compared to the 1.5 hour biological half-life of NAC in the bloodstream.* Protected by U.S. Patent # 6,623,754.