The suspicious ingredient is caffeine — a little more than the amount in a run-of-the-mill McDonald's coffee and maybe less than half as much as you'd get in something concocted by Starbucks. If caffeine like that was lethal the streets would be strewn with the corpses of hipsters.
I suspect that 13 is a small number in proportion to the number of people drinking the stuff, and that the people who died were engaging in other dangerous behavior. (That is, that the product appeals to people who are looking for a way to keep going, as if by magic, when it's really time to stop.)
Here, you can buy 5-hour Energy on Amazon. I predict you'll survive.