Even Kim Kardashian made her foray into the aisle with her drink Update, which is described as a caffeine-free energy drink. You may be asking yourself how an energy drink can be caffeine-free, and it’s not an oxymoron—it’s paraxanthine. Paraxanthine also has a shorter half-life than caffeine, so it clears out of your system faster than caffeine, preventing the known caffeine crash. Blatner warns: “Although it’s not equivalent to caffeine, paraxanthine is still a stimulant and should be taken in moderation. “Coffee in the morning plus paraxanthine in an energy drink later means you’re using two closely related stimulants, even if the energy drink says ‘caffeine-free,’” Blatner explains.