What is the cynical side effects of getting b12 shots?

What is the cynical side effects of getting b12 shots?
I used to get them years ago; contained by the butt. It is not comfortable getting shots in the butt. Besides that, the first 3 days I have energy approaching you would not believe!
Other than soreness at the injection site, I know of no negative side effects from B12 injections.
There are none. It is non-toxic. Of course, that's assuming nearby isn't anything else in the shot which is toxic, resembling a mercury-based preservative.