Study: Some energy drinks list inaccurate caffeine content

There is no secret to why energy drinks give you a boost; caffeine is one of the key ingredients in these drinks.

But it can be hard to determine just how much caffeine one can contains, according to a new round of tests conducted by Consumer Reports. The editors reached this conclusion after conducting lab tests on dozens of top-selling energy drinks.

Celebrities from Tim Tebow to 50 Cent, to Joan Rivers are advertising energy drinks these days. With their Facebook pages and Internet video campaigns, manufacturers specifically target young people.

But Consumer Reports says you have to be careful about how much caffeine you drink.

"It can quicken your pulse, cause abnormal heart rhythms, keep you from sleeping well, and elevate your blood pressure," said Gayle Williams of Consumer Reports.

Consumer Reports analyzed the caffeine content of 27 top-selling energy drinks, testing three samples of each. Although some list the amount of caffeine on the package, they're not required to.

And Consumer Reports found the numbers can be way off.

"Some of the energy drinks underestimated the amount of caffeine listed on the label by 20 percent or more," said Williams.

So how much caffeine do energy drinks contain? In Consumer Reports' tests, it varied widely.

For example, FRS Healthy Energy averaged 17 milligrams per container. Red Bull and S-K Street Kings Energy contained around 80 milligrams. 5-Hour energy contains 215 milligrams of caffeine, and and 5-Hour Energy Extra Strength has 242 milligrams.

Most healthy adults can consume up to 400 milligrams of caffeine per day. Both consumer and scientific groups have urged the Food and Drug Administration to require companies to disclose caffeine levels, but the agency says it doesn't have the authority to do so.

Many energy drinks do carry warnings: that they are not for children, women who are pregnant or nursing women, or people sensitive to caffeine.

"So for many people, an occasional energy drink is probably OK," Williams said.