It varies. But I have used up too .5cc's 4x/week.
It is my dream to do this. Where do you get the injectable b12?
a girl i work with got it from her doc. she takes 1 ml once a week
1 mL per week usually works well enough. There is no LD50 for b12 but it's just a matter of finding the amount your body seems to be lacking. Subjective, I know.
1ml EOD for me when I took it.