S-Acetyl-L-Glutathione (SAG) is a derivative of the antioxidant glutathione, which plays a crucial role in protecting cells from oxidative stress and maintaining cellular function. SAG is modified to enhance its stability and bioavailability compared to the native glutathione. S-Acetyl-L-Glutathione is not naturally occurring; it is synthesized chemically by acetylating glutathione. This modification is designed to enhance its stability and absorption when ingested.