From the United States Food and Drug Administration:
FDA Consumer Advice on Powdered Pure Caffeine
The FDA is warning about powdered pure caffeine being marketed directly to consumers, and recommends avoiding these products. In particular, FDA is concerned about powdered pure caffeine sold in bulk bags over the internet.
The FDA is aware of at least one death of a teenager who used these products.
These products are essentially 100 percent caffeine. A single teaspoon of pure caffeine is roughly equivalent to the amount in 25 cups of coffee.
Pure caffeine is a powerful stimulant and very small amounts may cause accidental overdose. Parents should be aware that these products may be attractive to young people.
Symptoms of caffeine overdose can include rapid or dangerously erratic heartbeat, seizures and death. Vomiting, diarrhea, stupor and disorientation are also symptoms of caffeine toxicity. These symptoms are likely to be much more severe than those resulting from drinking too much coffee, tea or other caffeinated beverages.
I could not imagine anyone willingly putting this into their bodies. Yes, I drink coffee and love that caffeine buzz (and get headaches when in withdrawal) but to seek out 100% pure is just unreal.
As Paracelsus said: Sola dosis facit venenum
