Consumer Reports tested a dozen of these carbonated drinks to see just where all the energy comes from.
"Many of these drinks are loaded with caffeine," says Consumer Reports Jamie Hirsh, "but often there's no way of telling how much because the government doesn't require manufacturers to label it. "
Consumer Reports analyzed samples of the drinks to determine the exact amount of caffeine.
This bottle of Celsius had the most amount of caffeine, 200 milligrams. That's about two cups of coffee. Archer Farms from Target had the least, around 50 milligrams per serving.
But the buzz doesn't stop there.
"Many of these drinks contain ginseng, which can amplify the effects of caffeine" says Hirsh.
Energy isn't all you're getting. Some of these drinks have more than 200 calories per container.
The bottom line?
"Around 300 milligrams a day of caffeine is considered fine for most adults, so it's O.K. to enjoy an occasional energy drink. But you should try to choose the low-calorie version to avoid getting too much sugar and calories" says Hirsh.
Most of the energy drinks carry warnings that if you're pregnant or nursing or sensitive to caffeine, you should avoid these energy drinks. Consumer Reports says that's good advice. Consumer Reports also points out mixing these drinks with alcohol can mask intoxication, so you should avoid that, too.