High-dose intravenous vitamin C, a common ingredient in Myers'-Cocktail-style wellness IV formulas, shows no consistent excess harm compared with placebo across nine double-blind randomized controlled trials, but the wider literature of 74 studies documents real complications including oxalate nephropathy, hypernatremia, and hemolysis in patients with G6PD deficiency.
Source
Harm of IV High-Dose Vitamin C Therapy in Adult Patients: A Scoping Review — Critical Care Medicine · 2020