I have to give myself shots of B12 as my stomach doesn't absorb it. You can't overdose on it. But realize that not all the other stuff in those energy drinks are as innocuous as the cyanocobalamin.
The cyano part is cyanide that is used to bind to the cobalamin or cobalt part. But don't worry, it's way to low a dose to ever be an issue. Though I use hydroxocobalamin now instead of cyanocobalamin.