The reason is multiple factors that influence the effect of glutathione IV , such as individual lifestyle, unique metabolism, general health, purpose and desired results
Vitamin C can be taken at the same time to provide antioxidant support
doi:10.1016/0731-7085(92)80092-2 Fatta-Kassinos D, Meric S, Nikolaou A (2011a) Pharmaceutical residues in environmental waters and wastewater: current state of knowledge and future research
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In general, any protein that may be recognized as an antigen (foreign protein) will induce a humoral immune response upon injection and will most likely give a positive testing result in rodent assays
Any combination claim would require direct evidence for the exact compounds, ratio, formulation, route, dose, analytical method, safety profile, study population, and condition being studied