Panera used to sell a drink that contained close to the FDA maximum recommended daily quantity of caffeine, and also allowed free refills. Several people died, and sales were halted after some wrongful death lawsuits.

This isn't to say that caffeine is dangerous. Danger isn't an intrinsic property of a substance but rather an emergent property of the context in which it is used. (This is why the schedules of the Controlled Substance Act are inherently stupid.)