Intracellular Antioxidant. Vegan. Gluten Free. Dietary Supplement. Non GMO Certified by NSF. Glutathione is the most abundant intracellular thiol (i.e., a compound containing a sulfhydryl [SH] group) and low molecular weight tripeptide found in living cells. The antioxidant functions of Glutathione Reduced include recycling vitamins E and C and serving as an antioxidant in all types of tissues.