b12 injections self administered Ivy Grove Surgery : Self-administration of injection B12 Shots at Home: NHS

A vitamin B12 deficiency can not only diminish your ability to lose weight, but it can lead to many serious health issues, some of which are irreversible, so if you are having or have had problems with your gut, are older in age, or follow a specialized or restrictive weight loss diet, dont hesitate to get tested.

This study did not include the use of testosterone

The deficiency rate at a cutoff of less than 211 pg/mL (156 pmol/L) at admission to a long-term care facility, according to one study, was 14%, and 38% of these older adults had levels lower than 407 pg/mL (300 pmol/L) [44]

And you dont have to worry about getting too much because its been reported that there are no reports of adverse effects associated with excess B12 intakebut thats not true