is taking glutathione orally safe Effects of Oral Supplementation on Systemic Oxidative Stress Biomarkers in Human Volunteers Glutathione: Benefits and Supplements

Positive-result publication bias affects both literatures

Cancer Research , 76 (18), 52775287

Serum samples were assayed for general clinical chemistry markers [i.e., glucose, total protein, blood urea nitrogen (BUN), creatinine, BUN/creatinine ratio, uric acid, aspartate aminotransferase (AST), alanine aminotransferase (ALT), creatine kinase (CK), lactate dehydrogenase (LDH), gamma glutamyl transferase (GGT), albumin, globulin, sodium, chloride, calcium, carbon dioxide, total bilirubin, alkaline phosphatase, triglycerides, cholesterol, high density lipoprotein (HDL), and lower density lipoprotein (LDL)]

I've looked, and I can't find consistent documentation about which independent labs they use, if any