I believe powdered caffiene is all but banned in a lot of places since it's basically lethal. Guess I can't say how that differs from pills, but there were a few deaths associated with it in powdered form.
I imagine it would be a lot like death from Aspirin or other OTC meds. They bore a hole through your stomach and you die from internal bleeding. Although your adrenal glands would probably fail hard. Horrible way, I imagine.
Edit: top of page. Fuck.
WELCOME NOOBLETS. Don't do anything stupid!