b12 injections hashimoto's : r/Hashimotos Where Do I Start With
Description
Intravenous (IV) use is less common and only done in clinical settings

doi:10.1136/bcr-2013-200380 Desai HG, Gupte PA
Vitamin B12 injections are the most common way to prevent or treat a deficiency.
Obesity Reviews (2016)

Vitamin B12, aka cobalamin, is an essential nutrient that plays an important role in overall health

The 50100mg range appears in protocols because it approximates allometric scaling from effective rodent doses, but rigorous human pharmacokinetic data validating those numbers is sparse
