Red bull is not the strongest energy drink at all. I need to chug 2 of the normal size cans in succession to feel anything at all. Monster and Rock Star are fantastic if you need to keep up physical work but I worry about their effect on my heart after reading about how bad they can be.

http://www.reuters.com/article/healthNews/idUSSYD58461200808...

Here is a sortable table of caffeine amounts in products. The numbers are quite striking.

http://www.energyfiend.com/the-caffeine-database

For example (mg caff / oz):

Red Bull = 80 / 8.46

Rockstar = 160 / 16

Coca Cola = 35 / 12

Fixx Energy = 400 / .17

I haven't drank Red Bull in a few years so things may have changed.

I checked the amounts of caffeine and other "medicinal" ingredients myself when I was doing physical labour and drank them regularly.

Surprisingly drinking chocolate has a few mg of caffeine also.