Please note that that particular drink has only about the caffeine of one cup of coffee. I thought they were great until they started to cause trouble by lasting much too long when I used them too many days in a row. Mileage may vary.

The other ones with guarana (almost 100% caffeine) are especially dangerous in my view. 5-Hour Energy seems to me to be the least likely to have ill effects of all of the ones I have looked at.