Consumer Reports tested more than two dozen energy drinks to determine caffeine levels and found that some had inaccurate labels.
Consumer Reports analyzed the caffeine content of 27 top-selling energy drinks. Companies are not required to list the content on their packaging. Of the 16 that did, Consumer Reports found the numbers were off on about a third of them.
"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.
Some of the energy drinks tested underestimated the amount of caffeine listed on the label by 20 percent or more said Williams.
Here are the results of the tests:
FRS Healthy Energy averaged 17 milligrams per container
Red Bull and Street King Energy around 80 milligrams
5-Hour Energy had 215 milligrams and 5-hour Energy Extra Strength had 242 milligrams
Experts say most healthy adults can consume up to 400 milligrams of caffeine a day.
"So for many people, an occasional energy drink is probably okay," said Williams.
As an alternative, regular coffee in an eight-ounce cup contains roughly 100 milligrams of caffeine.
Consumer and scientific groups have urged the Food and Drug Administration to require companies to disclose caffeine levels, but the agency say it lacks 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.