The fine print on the aluminum cylinder's side struck Keith Wiedenfeld as funny, but he heeded Monster Energy's request nonetheless.

"Consume responsibly – limit 3 cans per day," reads the black can displaying Monster's signature tattered, neon-green "M."

Wiedenfeld, a freshman at McHenry County College, would grab a Monster and a Snickers bar each day before his lunchtime shift in the Culver's kitchen. That was all he needed until, he said, the effect dulled. Wiedenfeld switched to Rockstar, but that just made him anxious and jittery.