Glutathione: The Bodys Master Antioxidant, ., ., Glutathione (GSH) is often referred to by scientists and nutritionists as the "Master Antioxidant." Unlike other antioxidants like Vitamin C or E, Glutathione Supplements: A Complete Guide Glutathione is the body's primary internal antioxidant, made using the amino acid cysteine, and it helps protect cells from oxidative stress. Beyond detoxification, research shows glutathione is involved in thyroid hormone metabolism, What Is Reduced Glutathione? Benefits, Sources & Uses