in the reddit nootropics forum the other day there was a post from someone who almost accidently OD'd on caffeine.

Alot of the users there use caffeine powder, and he had his bags of powder mixed up with his vitamin c powder and almost drank a drink with multiple grams of caffeine in it. He realized it at the last second and stopped.

moral of the story: caffeine has a fairly low lethal dose and can be dangerous when using the powdered form