The US Food and Drug Administration (FDA) has issued a warning to consumers about powdered pure caffeine, especially products that are sold in bulk bags over the Internet (http://1.usa.gov/Ugb7Gn).
One teaspoon of pure caffeine is roughly equivalent to the amount of caffeine found in 25 cups of coffee, according to the FDA. Symptoms of caffeine overdose may include rapid or dangerously erratic heartbeat, seizures, vomiting, diarrhea, stupor, and disorientation. The FDA is aware of at least 1 death of a teenager who used the products.
Hampton T. FDA Alert on Pure Caffeine Powder. JAMA. 2014;312(8):779. doi:10.1001/jama.2014.10968