intramuscular injection glutathione doses IV dosage and frequency vary depending on individual needs and health goals. Here IM Injections - Revive at

notes that a significant number of people who are B12 deficient are unable to absorb the vitamin from food or supplements, and so need to inject it, which they can only do at their GP practice

However, more research is needed

The first covers any substance or combination of substances presented as having properties of preventing or treating disease in human beings. The second definition is: Any substance or combination of substances that may be used by, or administered to human beings with a view to restoring, correcting or modifying a physiological function by exerting a pharmacological immunological or metabolic action. While some grey-market peptides may fall under the first definition, David H Reissner, Chair of the Pharmacy Law and Ethics Association, argues that most grey-market peptides should fall within the second broader definition

So the evidence is there