Let’s talk about why high dose vitamin C is beneficial.
When vitamin C is administered at a high level, above a certain threshold, it goes from being an anti-oxidant to a pro-oxidant. Vitamin C or ascorbic acid as a pro-oxidant creates hydrogen peroxide extracellularly, outside of the cell. Healthy cells have an enzyme called catalase, which can breakdown peroxide so that it is harmless to the cell. Unhealthy cells, including cancer cells, tend to be catalase-deficient. So when the peroxide is brought into the cells, it is quite damaging to those unhealthy cells.
Therefore, high dose vitamin C IVs are cytotoxic to cancer cells and there is no damage to healthy cells, meaning that there are minimal side effects.
C Klingelhoeffer, U Kämmerer, M Koospal, B Mühling, M Schneider, Mi Kapp, A Kübler, C Germer & C Otto. Natural resistance to ascorbic acid induced oxidative stress is mainly mediated by catalase activity in human cancer cells and catalase-silencing sensitizes to oxidative stress.BMC Complementary and Alternative Medicine volume 12: 61 (2012) [https://bmccomplementmedtherapies.biomedcentral.com/articles/10.1186/1472-6882-12-61]