glutathione is an essential tripeptide - The Amazing Detoxification Molecule You Might Not Know Optimal Health Systems Essential Glutathione
Description
Although DNA repair is an important marker for cisplatin resistance, we have shown that neither repair proteins expression nor DNA repair capacity analysis alone can predict patient response to the treatment

doi: 10.18632/oncotarget.8604
In addition to protecting cells from oxidative damage, glutathione plays a crucial role in the regeneration of other antioxidants, such as vitamins C and E, further reinforcing its ability to maintain oxidative balance in the body

Because your body does not readily store excess amounts, toxicity from B12 is very unlikely, even at the higher doses used in injections