Experts have said that the latest 'energy- shots' that seem to have caught everyone's fancy may be nothing but slightly caffeinated, sour-tasting water.
They said that the four-dollar a bottle drinks create nothing but a placebo effect.
The drink makers are not required to list how much caffeine they contain, nor does the law require them to be FDA approved.
"They don't have to prove safety or efficacy, so you have no idea if what it says on the labels is true. You have no idea what you're actually drinking or how much caffeine you're ingesting. It's a crap shoot," the New York Post quoted NYU nutritionist Marion Nestle as saying.
A Stacker2 6-Hour Power spokeswoman responded, "Listing the caffeine is not necessary. The energy you receive is not just from caffeine, it comes from the proprietary blend as a whole."
Some consumers said that they haven't felt any difference whatsoever from the drinks.
"It doesn't do anything for me. A cup of coffee works better," said Mirian Aguilar, 24, a saleswoman who admitted trying 5-hour Energy when she's dragging.
The drink labels purport to provide 2,000 percent of the daily dose of vitamin B6 and up to 8,666 percent of vitamin B12 -- claims that nutritionists dismissed as bogus at best and harmful at worst.
Too much B6 can lead to nerve damage in the arms and legs, said nutritionist Marissa Lippert.