IV potassium or magnesium?

[ladylazarus4]

So I know that a potassium overdose intravenously is pretty good at stopping the heart. Not sure about magnesium but I know that an IV overdose of magnesium can kill a horse pretty easily so maybe it would work too? Anyway this is more of a hypothetical. But let's say that I have a way of injecting myself (I do- when I go to ketamine I could inject through the place the nurses use to flush my tube and I have access to a bunch of needles/syringes because of my job with horses). How much potassium would I need to use? How quickly would it work? And would it be super noticeable?? Also, I'd obviously be on ketamine, so idk if that would affect it at all.

Again, this is just a hypothetical because I would never put the nurses at my ketamine place in such a position. So leave morals out of the equation.