„While poisonings or deaths caused by caffeine are rare, they do happen. Even specialists can make mistakes, as was seen in a Northumbria University trial that accidentally gave two students 30 g of powdered caffeine (equivalent to about 300 cups of coffee), when they should have received 0.3 g (300 mg). Both students survived, but they were hospitalized for some time.“
People mixing their own pre-workout often make this mistake and drop in a tbs or more of caffeine which can and often does kill people. Caffeine is a risky substance when you utilize it in a purified form - a risk with many drugs where the active dose is so small.